Firebird Documentation Index → Firebird Wire Protocol

Firebird Wire Protocol

1. Introduction

This document describes the Firebird wire protocol. Most of the information was obtained by studying the Firebird source code and implementing the wire protocol in the Firebird .NET provider and Jaybird (Firebird JDBC driver). The protocol is described in the form of the message sent by the client and received from the server. The described protocol is Firebird/InterBase protocol version 10. Earlier (InterBase) versions of the protocol are not in scope for this document. Changes in later protocol versions are described in notes below the description of the relevant version 10 message (currently higher versions are only partially described), or the base message introduced in a later protocol version. Protocol changes to an existing message are generally additive (new fields are added to the end of a message) and cumulative (also apply for higher protocol versions), unless explicitly indicated otherwise. This document is not complete. Consult the InterBase 6 API Guide for additional information on subjects like parsing the status vector, information request items, and the meaning of operations. You can find this manual under “InterBase 6.0 Manuals” in the Reference Manuals section of the Firebird website. We also recommend consulting the Firebird sources and other wire protocol implementations. Unless otherwise indicated, a client request must be flushed to the server for processing. For some operations the flush can be deferred, so it is sent together with a different operation. Versions 11 and higher of the wire protocol explicitly support (or even require) deferring of operations, including deferring the read of the response. In the protocol descriptions below, we include the names of the fields of the structs used in the Firebird sources; this can make it easier to search for how it’s used in Firebird itself.

2. Protocol versions

Below is a high-level overview of the changes per protocol versions. Be aware that protocol version greater than 10 are OR’ed with 0x8000 (FB_PROTOCOL_FLAG) to differentiate them from newer InterBase protocol versions with the same number. In message exchanges like Identification (connect), this masked version is used, while for example the database info item fb_info_protocol_version reports the bare version.

2.1. Protocol 10

The “baseline” protocol of this document. It was introduced in InterBase 6.0, and available in Firebird 1.0 and higher.

2.2. Protocol 11

Protocol 11 was introduced in Firebird 2.1. It introduces support for batching of messages, and lazy — or deferred — responses. Specifically, it allows you to batch a message creating an object (e.g. a statement or blob), with subsequent operations on that object (e.g. information request, statement prepare, blob get, etc.) by using the invalid object handle (0xFFFF) instead of the actual handle. This reduces latency, as you don’t have to wait for the server response to the create operation — containing the actual handle — before you can use the object. In some cases, with ptype_lazy_send, the server will defer the response to an operation until a subsequent operation is performed. For example, the response to statement allocation (op_allocate) is withheld, in the expectation that a prepare (op_prepare) follows immediately. Similarly, freeing a statement (op_free_statement) will not send its response immediately. This means that processing the response to a free can only be done later, after sending another operation, and before processing the response to that other operation.

The invalid object handle refers to the latest object created. So, while you can batch multiple create operations with use of those objects in a single send, you cannot interleave operations on different objects.

That is, “create object1, use object1, create object2, use object2” will work, but “create object1, create object2, use object1, use object2” will not work or result in unwanted effects, as after create object2 handle 0xFFFF refers to object2, not object1.

Protocol 11 also introduced “trusted” authentication, which is not (yet) documented.

2.3. Protocol 12

Protocol 12 was introduced in Firebird 2.5. It provides asynchronous cancellation support.

2.4. Protocol 13

Protocol 13 was introduced in Firebird 3.0. It provides the following new features: Authentication plugin support Wire protocol encryption Wire protocol compression Database encryption key callback Packed (NULL-aware) row data

2.5. Protocol 14

Protocol 14 was introduced in Firebird 3.0.1 to fix a bug in Database encryption key callback. We recommend skipping separate implementation of this protocol version, and implement it as part of protocol 15.

2.6. Protocol 15

Protocol 15 was introduced in Firebird 3.0.2 and provides the following new features: Support for Database encryption key callback in the connect phase. This allows connections to encrypted databases that serve as their own security database.

2.7. Protocol 16

Protocol 16 was introduced in Firebird 4.0 and provides the following new features: Statement timeouts

2.8. Protocol 17

Protocol 17 was introduced in Firebird 4.0.1 and provides the following new features: Sync batch Batch information request

2.9. Protocol 18

Protocol 18 was introduced in Firebird 5.0 and provides the following new features: Scrollable cursors (see Execute, Fetch scroll, and Cursor information request)

2.10. Protocol 19

Protocol 19 was introduced in Firebird 5.0.3 and provides the following new features: Inline blobs (see Inline blob response, Fetch response, Execute, and Fetch)

3. Common responses

The wire protocol has a limited set of responses. Some operations have a specific response, which is described together with the operation. Most operation, however, use one (or more) of the responses described in this section. The meaning and content depend on the operation that initiated the response.

3.1. Generic response

Int32 — p_operation Operation code If operation equals op_response — 9: Int32 — p_resp_object Object handle Although 32-bit in the protocol, valid handle values are always between 0 and 65535 (0xFFFF), with the “normal” range between 0 and 65000, where 0 either represents the connection itself, or means “no value”. Int64 — p_resp_blob_id Object ID Buffer — p_resp_data Data (meaning depends on the operation). Byte[] — p_resp_status_vector Status vector The format of the status vector is <tag><value>[{tag><value>} ...]<end>, with <tag>anInt32, and where parsing of <value> depends on <tag>; <end>isInt32 isc_arg_end — 0. The length can only be determined by correctly parsing the status vector. The first 8 bytes are always an Int32 tag (isc_arg_gdsorisc_arg_warning) and an Int32 value. If the status vector starts with Int32 isc_arg_gds — 1 and the second Int32 is non-zero, it is a failure response. If it starts with Int32 isc_arg_warning — 18 and the second Int32 is non-zero, it is a success response with warning(s). Otherwise, if the second Int32 is zero, it is a success response

Information about parsing the status vector can be found in the Interbase 6 API Guide in the documentation set. It might also be advantageous to look at the sources of Firebird .NET Data ProviderorJaybird.

3.2. SQL response

Success response to op_execute2 (see Execute) or op_exec_immediate2 (not yet documented). Int32 — p_operation Operation code If operation equals op_sql_response — 78: Int32 — p_sqldata_messages Count of rows following response (in practice, only 1or0) Byte[] — Row data The row data is a sequence (0..1) of data rows with a special format, see Reading and writing row data . Its length follows from the output row BLR in the execute operation. You can also consider the row data not a part of the SQL response, but something that is sent after the SQL response.

3.3. Fetch response

Success response to op_fetch (see Fetch) and op_fetch_scroll (see Fetch scroll). Int32 — p_operation Operation code If operation equals op_fetch_response — 66: Int32 — p_sqldata_status Status 0 — success 100 — end of cursor Int32 — p_sqldata_messages Count of rows following response (in practice, only 1or0) A value of 0 indicates end-of-batch (fetch complete). Together with status 100, it also means end-of-cursor, otherwise there are more rows available for a next fetch. Byte[] — Row data The row data is a sequence (0..1) of data rows with a special format, see Reading and writing row data . Its length follows from the row BLR specified in the first fetch. You can also consider the row data not a part of the fetch response, but something that is sent after the fetch response. The success response to Fetch and Fetch scroll is not a single op_fetch_response, but a sequence of op_fetch_response and row data, or — since protocol 19 — a sequence containing a sequence of 0 or more op_inline_blob, op_fetch_response and row data. That is: Sequence of responses to a fetch

0..n <op-inline-blob ...> -- protocol 19 and higher
<op-fetch-response (status = 0, count = 1)>
<row-data>
0..n <op-inline_blob ...>  -- protocol 19 and higher
<op-fetch-response (status = 0, count = 1)>
<row-data>
...
if end-of-cursor:
  <op-fetch-response (status = 100, count = 0)>
else:
  <op-fetch-response (status = 0, count = 0)>

Firebird may return fewer rows than requested in FetchorFetch scroll, even if end-of-cursor is not yet reached.

3.4. Inline blob response

Introduced in protocol 19 (Firebird 5.0.3). Each op_inline_blob — 114 response contains a single blob. The response is sent as part of a stream of responses to Execute (specifically op_execute2), op_exec_immediate2 (not yet documented), Fetch, and Fetch scroll. Int32 — p_operation Operation code If operation equals op_inline_blob — 114: Int32 — p_tran_id Transaction handle The same transaction handle as used when executing the statement. Int64 — p_blob_id Blob id Buffer — p_blob_info All blob info Same encoding as p_resp_data in response to a blob information request with all blob information items. Buffer — p_blob_data Segmented blob data Same encoding as p_resp_data in response to Get segment). The transaction handle (p_tran_id) and blob id (p_blob_id) can — for example — be used as a key to look up inline blobs from a local — attachment specific — cache when the client wants to open a blob. Instead of remotely opening the blob and retrieving data or information from the server, the client can then serve the data from the inline blob. The server sends each blob of the row in the following Fetch response, or SQL response as an inline blob, if it fits within the specified p_sqldata_inline_blob_size (including segment lengths). It is up to the client to decide if they want to cache the inline blob or discard it (e.g. if the cache is full).

3.5. Slice response

Success response to Get slice.

This might not reflect actual encoding in the protocol.

Response to Get slice. Int32 — p_operation Operation code If operation equals op_slice — 60: Int32 — p_slr_length Slice length Int32 Slice length (possibly a buffer?, needs verification) Buffer Slice data

3.6. Dummy response

The server may occasionally send a “dummy” response. This is intended as a keep-alive feature, and is related to the DummyPacketInterval server setting and/or isc_dpb_dummy_packet_interval/isc_spb_dummy_packet_interval connection setting. Though Firebird normally uses SO_KEEPALIVE (which is transparent to the client), clients must be able to handle the dummy response. The appropriate action is to read and ignore this response, and continue with the next response. Int32 — p_operation Operation code (op_dummy — 71)

3.7. Exit or disconnect command (aux connection)

As far as we’re aware, this is only sent on the aux connection. It is similar to the disconnect request from client to server for the main connection.

Instructs the client to close the aux connection. Int32 — p_operation Operation code (op_exit — 2orop_disconnect — 6) After receiving this message, the client should close the aux connection. It’s generally only sent just before the main connection is closed.

4. Common requests

A few requests in the protocol have a common message format, where the operation code differs, and — possibly — the set of allowed values of other fields. We describe the request format here, and describe the allowed values in the section for a specific request.

4.1. Generic information request

Client

Int32 — p_operation Operation code (value depends on the actual operation) Int32 — p_info_object Object handle (e.g. statement, transaction, etc.) Int32 — p_info_incarnation Incarnation of object (0) TODO: Usage and meaning? Buffer — p_info_items Requested information items A list of requested information items (each byte is an information item), so-called SingleTpb items. Some operations may have items that do have values (e.g. isc_info_sql_sqlda_startofStatement information request). Most values are specific to the operation. The list should end with isc_info_end — 1^[1]. Int32 — p_info_buffer_length Length of buffer available for receiving response In protocol 10, this is a signed Int16, encoded as Int32. In protocol 11 and higher, this is an unsigned Int32. For compatibility reasons, values greater than or equal to 4,294,901,760 (i.e. 0xFFFF_0000 or greater) are masked with 0xFFFF, so only the low 16 bits are used. A too small value may lead to receiving a truncated buffer (last item is isc_info_truncated — 2 instead of isc_info_end — 1), which necessitates requesting information again with a larger size. Some operations may have additional mechanisms to handle truncation, like The buffer in the response is sized to the actual length of the response (upto the declared available length), so specifying a larger than necessary size does not inflate the response on the wire. However, specifying an unnecessarily large size can lead to inefficiencies for the server.

Server

Generic response — on success, p_resp_data holds the requested information. A truncated response is considered a success, and can only be determined by parsing p_resp_data.

Information about how to parse the information buffer sent by the Firebird server can be found in the InterBase 6.0 documentation set

5. Establishing connection

This chapter describes how to connect to a database or service. Other operations on a database or service, or information specific to connecting to a database or service are documented in Databases and Services.

5.1. Attaching to a database or service

In protocol 10 and 11, attachment to a database or service is done in two steps, first identification (connect) to the server, then attach to — or creation of — a database, or attach to a service. In protocol 13, this was changed to a more complex state machine to handle multiple authentication plugins, wire protocol encryption, and database encryption key callback. In deviation of the normal description in this documentation, and previous versions of this documentation, we will first cover the individual messages, and then explain the order and logic of message exchange.

5.2. Identification (connect)

Requests connection to the server and specifies which protocol versions the client can use. Int32 — p_operation Operation code (op_connect — 1) Int32 — p_cnct_operation Unused, always use 0 Some implementations use op_attach — 19/op_service_attach — 82 for historic(?) reasons. Int32 — p_cnct_cversion Connect version:

`CONNECT_VERSION2` — `2`	user identification encoding is undefined (Firebird 1.0 — Firebird 2.5)
`CONNECT_VERSION3` — `3`	user identification is UTF-8 encoded (since Firebird 3.0 and higher, but backwards compatible as the version wasn’t checked before Firebird 3.0)

Int32 — p_cnct_client Architecture type (e.g. arch_generic — 1). String — p_cnct_file Database path or alias The encoding of this is undefined, which can lead to problems with non-ASCII paths if the server and client use a different encoding. For a service connection, this value can be the service name (service_mgr or empty), or the “expected database” name (same value as isc_spb_expected_db). Int32 — p_cnct_count Count of protocol versions understood (e.g. 1). Buffer — p_cnct_user_id User identification TODO: Needs further description

The next block of data declares the protocol(s) that the client supports. It should be sent as many times as protocols are supported (and specified in p_cnct_count above). Values depend on the protocol.

If a client sends more than 10 (Firebird 5.0 and older) or 11 (Firebird 6.0) protocols, the surplus are ignored.

Int32 — p_cnct_version Protocol version (e.g. PROTOCOL_VERSION10 — 10).

Protocol versions greater than `10` need to be OR'ed with `0x8000` for differentiation from newer InterBase protocol versions.
For example, `PROTOCOL_VERSION11` is `0x8000 | 11` or `32779` (`0x800B`)

Int32 — p_cnct_architecture Architecture type (e.g. arch_generic — 1) It is possible to use a different architecture value, but then connection is only possible with a server of the same architecture. In addition, it changes how responses and/or data needs to be parsed or encoded (the authors don’t know the exact details). In short, use arch_generic. Int32 — p_cnct_min_type Minimum type (e.g. ptype_batch_send — 3) Connection type (ptype) values

`ptype_page` — `1`	Page server protocol (never supported in Firebird)
`ptype_rpc` — `2`	Simple remote procedure call (not supported since Firebird 3.0)
`ptype_batch_send` — `3`	Batch sends, no asynchrony
`ptype_out_of_band` — `4`	Batch sends w/ out of band notification (semantics not documented in this manual)
`ptype_lazy_send` — `5`	Deferred packets delivery

Int32 — p_cnct_max_type Maximum type (e.g. ptype_lazy_send — 5) If the client wants to set up wire compression, this ptype-code must be OR’ed with pflag_compress (0x100). See also Known p_acpt_type flags below. Int32 — p_cnct_weight Preference weight (e.g. 2). Higher values have higher preference. For equal weights, the last supported occurrence will be selected.

5.3. Simple accept

Specifies the protocol selected by the server. This response is — as far as we know — not sent if the server accepts protocol 13 or higher; then the extended Accept with data orconditional accept is sent instead. Int32 — p_operation Operation code If operation equals op_accept — 3: Int32 — p_acpt_version Protocol version accepted by server Int32 — p_acpt_architecture Architecture for protocol Int32 — p_acpt_type Accepted type and additional flags. Obtain the type by masking with 0xFF (p_acpt_type & 0xFF). Known p_acpt_type flags

`pflag_compress` — `0x100`	Turn on compression From client to server, it signals a request to use wire compression. From server to client, it is an acknowledgement, and wire compression must be enabled after reading this entire response, but before reading or writing any other messages.
`pflag_win_sspi_nego` — `0x200`	Win_SSPI supports Negotiate security package Only sent from server to client.

Failure response: Generic response

5.4. Accept with data orconditional accept

Introduced in protocol 13. The op_accept_data — 94 and op_cond_accept — 98 responses start with the same fields as Simple accept, followed by additional fields for authentication and encryption purposes. Int32 — p_operation Operation code If operation equals op_accept_data — 94orop_cond_accept — 98: Int32 — p_acpt_version Protocol version number accepted by server Int32 — p_acpt_architecture Architecture for protocol Int32 — p_acpt_type Accepted type and additional flags. See also p_acpt_typeinop_accept message Buffer — p_acpt_data Authentication plugin data String — p_acpt_plugin Authentication plugin to continue with Int32 — p_acpt_authenticated Authentication complete in a single step (0 — false, 1 — true) This will generally only be 1ifLegacy_Auth was tried first, though third-party authentication plugins might also authenticate in a single step. Buffer — p_acpt_keys “Keys” known by the server (used for configuring authentication and wire encryption)

5.5. Continue authentication

Introduced in protocol 13(?). This message is used both by client and server to exchange authentication information. Int32 — p_operation Operation code (op_cont_auth — 92) Buffer — p_data Authentication data String — p_name Name of the current authentication plugin String — p_list On first authentication from client to server: list of (remaining) plugins known to the client, including the current plugin; on subsequent authentication from client to server, or from server: empty The list of plugin names can be separated by space, tab, comma or semicolon. Buffer — p_keys From client to server: empty; from server to client: “keys” known by the server (used for configuring authentication and wire encryption)

5.6. Trusted authentication

Introduced in protocol 11. Int32 — p_operation Operation code (op_trusted_auth — 90) Buffer — p_trau_data Trusted authentication data

5.7. Database encryption key callback

Introduced in protocol 13. Used to exchange information between the client and server parts of a database encryption plugin for the encryption key. The server sends this message, and the client responds with the same message type. Specifics of the message exchange depends on database encryption plugin. It is possible that multiple message of this type are exchanged. In protocol 13, this message can only occur after authentication and — optionally — establishing wire protocol encryption. In protocol 15 and higher, it can also occur immediately after op_connect, if the database is its own security database and is encrypted. If this message is received before op_accept/op_accept_data/op_cond_accept (so no protocol version has been confirmed yet), you need to assume protocol 15 behaviour for this message and the client response. Int32 — p_operation Operation code (op_crypt_key_callback — 97) Buffer — p_cc_data Crypt callback data

Additions in protocol 14

Int32 — p_cc_reply Maximum expected reply size (16-bit signed integer encoded as 32-bit int) Judging by the code in Firebird for protocol 14 and higher, this value may be negative, and should then be considered equivalent to 1. From client to server, the reply size should be 0.

5.8. Enable wire encryption

Introduced in protocol 13. Enables wire encryption by telling the server the selected plugin and key type.

Client

Int32 — p_operation Operation code (op_crypt — 96) String — p_plugin Selected wire encryption plugin String — p_key Selected key type After sending this message, the client must set up wire encryption both for sending and receiving data. Subsequent messages — including the server response to this message — must be sent or received with encryption enabled.

Server

Generic response

5.9. Attachment to database or service

This message is used for: Attaching to a database (op_attach — 19) — see also Attach database Creating a database (op_create — 20) — see also Create database Attaching to a service (op_service_attach — 82) — see also Attach

Client

Int32 — p_operation Operation code (op_attach — 19, op_create — 20, or op_service_attach — 82) Int32 — p_atch_database Unused, always use 0 String — p_atch_file Database path or alias, or service name (e.g. service_mgr). Ifisc_dpb_utf8_filename is present in the database parameter buffer below, the encoding is UTF-8, otherwise, the encoding is undefined. The isc_dpb_utf8_filename item is supported since Firebird 2.5. Buffer — p_atch_dpb Database or service parameter buffer

Server

In protocol 10 and 11: Generic response In protocol 13 and higher: It’s complicated.

5.10. Connection rejection

Server response rejecting the connection. This is usually sent if op_connect only sent protocols the server can’t support. Int32 — p_operation Operation code (op_reject — 4) If this message is received, the client should report error isc_connect_reject (335544421) or equivalent.

5.11. Connection handshake

5.11.1. Protocol 10 — 12

For protocol 10 — 12, the connection handshake is pretty simple. Client → Identification (connect) Server ← op_accept — 3 — Server accepts and reports selected protocol, continue with step 3 ← op_reject — 4 — Server can’t fulfill the requested protocol Report error isc_connect_reject (335544421) or equivalent Close connection ← op_response — 9 — Error or other problem Ifp_resp_status_vector has an error, report it, otherwise report error isc_login (335544472) or equivalent Close connection Client → Attachment to database or service with op_attach, op_createorop_service_attach Server ← op_response — 9 Ifp_resp_status_vector has no error or only a warning, connection is successful and can be used for other operations Otherwise, connection is unsuccessful Report error Close connection (client → Disconnect)

5.11.2. Protocol 13 and higher

For protocol 13 and higher, the handshake is more complex.

This might not be the best way to document the connection handshake. We’re open to suggestions.

Client → Identification (connect) The p_user_identification should include: CNCT_plugin_name with the current authentication plugin CNCT_plugin_list with the authentication plugins supported by the client (including the current plugin); this list is separated by space, comma or semicolon CNCT_specific_data with authentication plugin data (NOTE: this tag has a special “multipart” encoding as the data is generally longer than the 255 bytes supported for a single tag value) Server ← op_crypt_key_callback — 97 (read as protocol 15) Client → Database encryption key callback (write as protocol 15) and continue with step 2 ← op_accept — 3 — Record selected protocol and type, continue with step 5 (attach) ← op_accept_data — 94orop_cond_accept — 98 Record the selected protocol and type, and use that for sending and receiving subsequent messages. Enable wire compression if acknowledged by server. Ifp_acpt_authenticated == 1, mark authentication completed Ifop_accept_data — 94, process the data, plugin and keys, and continue with step 5 (attach) Ifop_cond_accept — 98, continue with step 3 (pre-attach-auth), item for op_cond_accept ← op_reject — 4 — Server can’t accept any of the protocols or protocol options report error isc_connect_reject (335544421) or equivalent close connection ← op_response — 9 — Error or other problem Ifp_resp_status_vector has an error, report it, otherwise report error isc_login (335544472) or equivalent close connection (end of this flow) Server — pre-attach auth If the requested authentication plugin name (p_acpt_plugin/p_name) is non-empty and different from the current authentication plugin name, switch to that authentication plugin. If the client cannot fulfill the server request for an authentication plugin or has no current authentication plugin, error isc_login (335544472) or equivalent should be reported, and the connection closed (end of this flow) If coming from step 2, treat this as if op_cond_accept was just received. ← op_cond_accept — 98: process p_acpt_data, p_acpt_plugin and p_acpt_keys, and continue with step 4 ← op_cont_auth — 92: process p_data, p_name (plugin name) and p_keys, and continue with step 4 ← op_crypt_key_callback — 97 Client → Database encryption key callback and continue with step 3 (pre-attach auth) ← op_trusted_auth — 90 (not documented yet, probably only post-attach auth with protocol 11 and 12(?)) ← op_response — 9 Ifp_resp_statusvector has an error, report it and close the connection (end of this flow) Otherwise, this signals pre-attach auth (or post-attach auth) completed Process keys from p_resp_data If authentication was not previously completed, and wire encryption is not disabled, set up wire encryption Client → Enable wire encryption Set up wire encryption on incoming and outgoing stream Server ← op_response — 9: if p_resp_statusvector has error, report it and close connection (Disconnect), (end of flow) Mark authentication completed Continue with step 5 (attach); or if used as post-attach auth, attach successfully completed (end of flow) Client — pre-attach auth → Continue authentication with: p_data — authentication plugin data p_name — current authentication plugin p_list — list of remaining authentication plugins, including current plugin (separated by space, comma, or semicolon) This only needs to be sent once; for subsequent messages an empty buffer can be sent. Continue with step 3 (Server — pre-attach auth) Client — attach → Attachment to database or service with op_attach, op_createorop_service_attach If authentication was not yet complete at this point (as far as we know, only when op_accept — 3orop_accept_data — 94 was received in the previous step), and protocol 13 or higher was selected, the database or service parameter buffer should include the following tags: If protocol 13 or higher is used, the “wide” parameter buffer variant (isc_dpb_version2/isc_spb_version3 or higher) must be used given the size of the client authentication data (…_specific_auth_data). isc_dpb_auth_plugin_list/isc_spb_auth_plugin_list — with remaining authentication plugins (separated by space, comma or semicolon) isc_dpb_auth_plugin_name/isc_spb_auth_plugin_name — current authentication plugin isc_dpb_specific_auth_data/isc_spb_specific_auth_data — client authentication data It should not include any of these tags (if protocol 13 or higher): isc_dpb_password/isc_spb_password isc_dpb_password_enc/isc_spb_password_enc isc_dpb_trusted_auth/isc_spb_trusted_auth Server/client — post-attach auth This is the same as steps 3 and 4 (pre-attach auth), except op_cond_accept cannot occur, and its “Continue with step 5 (attach)” should be read as “Connection successful (end of flow)” (also noted there). If the pre-attach auth flow was previously entered, this will essentially be only an op_response — 9 with either an error or acceptance (connection success).

5.12. Detach

Detaches from the database (op_detach — 21) or service (op_service_detach — 83). After detach the connection is still open, to disconnect send Disconnect (op_disconnect).

Client

Int32 — p_operation Operation code (op_detach — 21, or op_service_detach — 83) Int32 — p_rlse_object Unused, always use 0

Server

Generic response

5.13. Disconnect

Client

Int32 — p_operation Operation code (op_disconnect)

Server

No response, remote socket close. Closing the connection (socket) without sending an op_disconnect will result in “Connection reset by peer” (error 10054 (Windows) or 104 (Linux)) in firebird.log.

6. Databases

6.1. Attach database

Attach to an existing database. Use message Attachment to database or service with op_attach — 19.

Table 1. Example of parameters sent in the DPB
Parameter	Description	Value	Optional
`isc_dpb_version1`	Version (must be first item!)
`isc_dpb_dummy_packet_interval`	Dummy packet interval	120	*
`isc_dpb_sql_dialect`	SQL dialect	3
`isc_dpb_lc_ctype`	Character set	UTF8
`isc_dpb_sql_role_name`	User role	RDB$ADMIN	*
`isc_dpb_connect_timeout`	Connection timeout	10	*
`isc_dpb_user_name`	User name	SYSDBA
`isc_dpb_password`	User password	masterkey

6.2. Create database

Create a database and connect to it. Create uses Attachment to database or service with p_operation op_create — 20. There are a number of DPB items to configure the newly created database, including page size (isc_dpb_page_size) — which cannot be modified after creation.

The `CREATE DATABASE` statement

Although Firebird has a CREATE DATABASE statement, the documented syntax is not fully supported by Firebird server. Part of the syntax (e.g. database name, user, password, page size) are parsed by fbclient to execute the op_create (or equivalent for embedded). After the database is successfully created, fbclient then uses execute immediate (op_execute_immediate) without transaction to execute a reduced CREATE DATABASE statement for additional configuration of the database.

6.3. Drop

Drops the currently attached database.

Client

Int32 — p_operation Operation code (op_drop_database) Int32 — p_rlse_object Unused, always use 0

Server

Generic response

6.4. Detach and disconnect

Send Detach with op_detach — 21, followed by Disconnect.

6.5. Database information request

Requests database or server information. Uses the Generic information request message with:

`p_operation`	`op_info_database` — `40`
`p_info_object`	Unused, always use `0`
`p_info_items`	Values of enum `db_info_types` in Firebird’s `inf_pub.h`.

6.6. Cancellation

Protocol 12 and higher. Cancels a running operation on the server.

Operation fb_cancel_abort — 4 should not be sent to the server, but instead the client should simply close the socket connection.

Client

Int32 — p_operation Operation code (op_cancel) Int32 — p_co_kind Cancellation kind, one of: fb_cancel_disable — 1 disable cancellation until fb_cancel_enable is sent fb_cancel_enable — 2 enable cancellation if it was disabled previously fb_cancel_raise — 3 cancel current operation fb_cancel_abort — 4 See note above, this kind should not be sent to the server. As cancellation is generally performed asynchronously to be effective, the client implementation must take special care how the operation is sent. For example, if you use a lock for socket operations, this operation will need to ignore it (running the risk of interfering/corrupting another send operation), or you need to split your locks in a lock for writing, and a lock for reading, or have some other way of detecting that another thread is not currently sending data.

Server

No formal response, cancellation is signalled as a Generic response with a failure for the cancelled operation.

Performs the first stage of a two-phase commit. After prepare, a transaction is in-limbo until committed or rolled back.

Request flushing and response processing can be deferred. Ifptype_batch_send or higher is used, other transaction operations can be sent immediately after reconnecting the transaction. They can use the invalid object handle (0xFFFF) instead of the — not yet received — transaction handle.

7.8. Transaction information request

Requests information on the transaction bound to the transaction handle. Uses the Generic information request message with:

`p_operation`	`op_info_transaction` — `42`
`p_info_object`	Transaction handle
`p_info_items`	Values of constants in Firebird’s `inf_pub.h` starting with `isc_info_tra_`or`fbinfo_tra_`.

8. Statements

8.1. Allocate

Allocates a statement handle on the server.

Client

Int32 — p_operation Operation code (op_allocate_statement — 62) Int32 — p_rlse_object Unused, always use 0

Server

Generic response — on success, p_resp_object is the allocated statement handle.

8.1.1. Deviations for protocol version 11

In protocol 11 and higher with ptype_lazy_send, the response to op_allocate_statement is deferred; it requires another operation on the connection before the response is sent. In general, this means the allocate operation should be sent together with a prepare operation using the invalid object handle (0xFFFF).

8.2. Free

Frees resources held by the statement.

Client

Int32 — p_operation Operation code (op_free_statement — 67) Int32 — p_sqlfree_statement Statement handle Int32 — p_sqlfree_option

`DSQL_close` — `1`	Closes the cursor opened after statement execute.
`DSQL_drop` — `2`	Releases the statement handle.
`DSQL_unprepare` — `4`	Firebird 2.5 or higher Close resources associated with statement handle, and unprepares the current statement text. The statement handle itself is retained. It is not necessary to unprepare before preparing a new statement text on the same handle.

The server treats these as flag values, so they can be combined with OR, but doing so makes little sense, as an unprepare also closes the cursor, and a drop effectively closes the cursor and unprepares the current statement text.

Server

Generic response

8.2.1. Deviations for protocol version 11

Request flushing can be deferred for ptype_batch_send or higher. For ptype_lazy_send, the response to op_free_statement is deferred; it requires another operation on the connection before the response is sent. For DSQL_drop and DSQL_unprepare, we recommend flushing immediately so the server at least processes the request, which will prevent longer than necessary retention of metadata locks.

8.3. Prepare

Client

Int32 — p_operation Operation code (op_prepare_statement — 68) Int32 — p_sqlst_transaction Transaction handle Int32 — p_sqlst_statement Statement handle Int32 — p_sqlst_SQL_dialect SQL dialect (1or3) This should generally match the connection dialect. String — p_sqlst_SQL_str Statement to be prepared Buffer — p_sqlst_items Statement information items, including describe and describe bind Example of requested information items isc_info_sql_select isc_info_sql_describe_vars isc_info_sql_sqlda_seq isc_info_sql_type isc_info_sql_sub_type isc_info_sql_length isc_info_sql_scale isc_info_sql_field isc_info_sql_relation Int32 — p_sqlst_buffer_length Target buffer length for information response See also the description of p_info_buffer_lengthinGeneric information request.

Server

Generic response — on success, p_resp_data holds the statement description (matching the requested information items) For statements with a lot of columns and/or parameters, it may be necessary to handle truncation of the buffer by repeating the describe and/or describe bind information request using Statement information request and using isc_info_sql_sqlda_start to inform the server from which column or parameter to continue. For an example, see Jaybird’s StatementInfoProcessor.handleTruncatedInfo(…).

8.3.1. Deviations for protocol version 11

The statement handle can no longer be allocated separately (or at least, its response is deferred). The initial Allocate operation must be sent together with the first prepare operation. When allocating and preparing together, the value of the statement handle of the prepare message must be 0xFFFF (invalid object handle). The responses must be processed in order: first allocate response, then prepare response. Once a statement handle has been allocated, it can be reused by sending a prepare message with its statement handle.

8.4. Describe

Requesting a description of output parameters (columns) of a query is done using the statement information request message Example of requested information items isc_info_sql_select isc_info_sql_describe_vars isc_info_sql_sqlda_seq isc_info_sql_type isc_info_sql_sub_type isc_info_sql_length isc_info_sql_scale isc_info_sql_field isc_info_sql_relation The initial request can be done as part of Prepare. The information can be requested together with Describe bind (input parameters).

8.5. Describe bind (input parameters)

Describe of input parameters of a query is done using the statement information request message Example of requested information items isc_info_sql_bind isc_info_sql_describe_vars isc_info_sql_sqlda_seq isc_info_sql_type isc_info_sql_sub_type isc_info_sql_length isc_info_sql_scale isc_info_sql_field isc_info_sql_relation The initial request can be done as part of Prepare. The information can be requested together with Describe.

8.6. Execute

Client

Int32 — p_operation Operation code

`op_execute` — `62`	DDL and DML statements
`op_execute2` — `76`	Executable stored procedures with return values, or singleton `RETURNING` (i.e. statements described as `isc_info_sql_stmt_exec_procedure`)

Int32 — p_sqldata_statement Statement handle Int32 — p_sqldata_transaction Transaction handle Buffer — p_sqldata_blr Row BLR of parameters If there are no parameters, send a zero-length buffer. Int32 — p_sqldata_message_number Unused, always use 0 Int32 — p_sqldata_messages Number of messages — 1 if there are parameters, 0 if there are no parameters Byte[] — Row data Row data of parameter values matching the row BLR specified in p_sqldata_blr Ifp_sqldata_messagesis0, nothing is sent If using op_execute2 — 76 (the statement is a stored procedure and there are output parameters): Buffer — p_sqldata_out_blr Row BLR of the output row Int32 — p_sqldata_out_message_number Unused, always use 0

Additions in protocol 16

UInt32 — p_sqldata_timeout Statement timeout value in milliseconds (0 — use connection-level statement timeout)

Additions in protocol 18

UInt32 — p_sqldata_cursor_flags Cursor flags

CURSOR_TYPE_SCROLLABLE — 0x01

request scrollable cursor

Additions in protocol 19

UInt32 — p_sqldata_inline_blob_size Maximum inline blob size A value of 0 disables inline blobs. The server may use a lower limit than requested. In the Firebird 5.0.3 and Firebird 6 implementation at the time of writing, the server has a maximum of 65535 bytes.

Server

For op_execute — 63: Generic response For op_execute2 — 76: Success response: ( zero or more Inline blob response ), SQL response followed by Generic response The Inline blob response messages are only included in protocol 19 or higher, and only if the statement was executed with a non-zero value for p_sqldata_inline_blob_size, and if the row has blobs smaller than that size. Failure response: only Generic response

8.7. Rows affected by query execution

Obtaining the rows affected by a query is done using the statement information request message List of requested information items isc_info_sql_records

8.8. Fetch

Client

Int32 — p_operation Operation code (op_fetch — 65) Int32 — p_sqldata_statement Statement handle Buffer — p_sqldata_blr Row BLR of the output rows Only needs to be sent on first fetch; subsequent fetches can send a zero-length buffer. Int32 — p_sqldata_message_number Message number (always 0) Int32 — p_sqldata_messages Message count/fetch size (e.g. 200) The server may decide to return fewer rows than requested, even if the end-of-cursor wasn’t reached yet.

Server

Success response: one or more ( zero or more Inline blob response ), Fetch response The Inline blob response messages are only included in protocol 19 or higher, and only if the statement was executed with a non-zero value for p_sqldata_inline_blob_size, and if the row has blobs smaller than that size. See also Sequence of responses to a fetch. Failure response: Generic response — with an error in p_resp_status_vector It is possible to receive Generic response with an error in the status vector after one or more fetch responses.

8.9. Fetch scroll

Introduced in protocol 18 (Firebird 5.0). Fetches from a scrollable cursor. This message is an extended version of Fetch.

Client

Int32 — p_operation Operation code (op_fetch_scroll — 112) Int32 — p_sqldata_statement Statement handle Buffer — p_sqldata_blr Row BLR of the output rows Only needs to be sent on first fetch; subsequent fetches can send a zero-length buffer. Int32 — p_sqldata_message_number Unused, always use 0 Int32 — p_sqldata_messages Message count/fetch size (e.g. 200) The server may decide to return fewer rows than requested, even if the end-of-cursor wasn’t reached yet. Ignored for p_sqldata_fetch_op other than fetch_next, or if the statement is a SELECT … FOR UPDATE; for those fetch operations or conditions, at most 1 row is fetched. Int32 — p_sqldata_fetch_op Fetch operation Valid values (see also enum P_FETCHinprotocol.h):

`fetch_next` — `0`	Fetch next rows (same as using Fetch)
`fetch_prior` — `1`	Fetch previous row
`fetch_first` — `2`	Fetch first row
`fetch_last` — `3`	Fetch last row
`fetch_absolute` — `4`	Fetch row by absolute position Negative values of `p_sqldata_fetch_pos` are from the end of the cursor (i.e. `-1` is the last row, `-2` the row before the last row, etc.)
`fetch_relative` — `5`	Fetch row relative to the current position of the server-side cursor

If the current cursor is not a scrollable cursor, only fetch_next is accepted. Int32 — p_sqldata_fetch_pos Requested position Ignored if p_sqldata_fetch_op is not fetch_absoluteorfetch_relative.

If combining fetch_next with a fetch size greater than 1 with other scroll operations, you may need to keep your own position accounting to ensure you scroll to the right row.

Server

8.10. Set cursor name

Client

Int32 — p_operation Operation code (op_set_cursor — 69) Int32 — p_sqlcur_statement Statement handle String — p_sqlcur_cursor_name Cursor name (null terminated!) Int32 — p_sqlcur_type Cursor type Reserved for future use, always use 0.

Server

Generic response

8.11. Statement information request

Requests information on the statement prepared on the statement handle, including information on its input parameters and output columns or parameters, or information on the server-side statement handle itself. Uses the Generic information request message with:

`p_operation`	`op_info_sql` — `70`
`p_info_object`	Statement handle
`p_info_items`	Values of constants in Firebird’s `inf_pub.h` starting with `isc_info_sql_`.

8.12. Cursor information request

Requests information on an open cursor of a statement handle. Uses the Generic information request message with:

p_operation

op_info_cursor — 113

p_info_object

Statement handle

p_info_items

Values of constants in Firebird’s IResultSet class in IdlFbInterfaces.h starting with INF_.

Known items:

INF_RECORD_COUNT — 10

Cursor size (total number of records in scrollable cursor)

If the cursor is not scrollable, the returned value is -1 to indicate the value is unknown.

This request should only be sent after at least one fetch (FetchorFetch scroll). Attempts to request cursor information between execute and the first fetch may result in SQLDA errors on fetch.

9. Blobs

9.1. Create/Open

Client

Int32 — p_operation Operation code

`op_create_blob` — `34`	Creates a new blob
`op_create_blob2` — `57`	Creates a new blob with a blob parameter buffer
`op_open_blob` — `35`	Opens an existing blob
`op_open_blob2` — `56`	Opens an existing blob with a blob parameter buffer

Buffer — p_blob_bpb Blob parameter buffer Only sent for op_create_blob2 — 57 and op_open_blob2 — 56. Int32 — p_blob_transaction Transaction handle Int64 — p_blob_id Blob ID

Server

Generic response — on success + p_resp_object is the blob handle p_resp_blob_id is the blob id (for op_create_blob --35/ op_create_blob2 — 57)

9.1.1. Deviations for protocol version 11

Request flushing and response processing can be deferred. Ifptype_batch_send or higher is used, other blob operations can be sent immediately after the open/create. They can use the invalid object handle (0xFFFF) instead of the — not yet received — blob handle.

9.2. Get segment

Client

Int32 — p_operation Operation code (op_get_segment — 36) Int32 — p_sgmt_blob Blob handle Int32 — p_sgmt_length Segment length Maximum length is 32767 for Firebird 2.5 and older, 65535 for Firebird 3.0 and higher. Buffer — p_sgmt_segment Always a zero-length buffer

Server

Generic response — on success, p_resp_data is the blob segment The response buffer in p_resp_data contains zero or more segments. Each segment starts with 2-bytes for the length (little-endian), followed by that length of data.

9.2.1. Deviations for protocol version 11

Request flushing and response processing can be deferred. Ifptype_batch_send or higher is used, op_get_segment can be batched with Create/Open (and other blob operations) by using the invalid object handle (0xFFFF).

9.3. Put segment

10. Arrays

10.1. Get slice

Client

Int32 — p_operation Operation code (op_get_slice — 58) Int32 — p_slc_transaction Transaction handle Int64 — p_slc_id Array handle Int32 — p_slc_length Slice length Buffer — p_slc_sdl Slice descriptor (SDL) Buffer — p_slc_parameters Slice parameters (always empty?, needs verification) Buffer — p_slc_slice Slice data (always empty)

Server

Success response: Slice response Failure response: Generic response

10.2. Put slice

Client

Int32 — p_operation Operation code (op_put_slice — 59) Int32 — p_slc_transaction transaction handle Int64 — p_slc_id Array handle Int32 — p_slc_length Slice length Buffer — p_slc_sdl Slice descriptor (SDL) Buffer — p_slc_parameters Slice parameters (always empty?, needs verification) Buffer` — p_slc_slice Slice data

Server

Generic response — on success, p_resp_blob_id is the array handle.

11. Batches

Statement batches were introduced in protocol 16 (Firebird 4.0).

11.1. Create

Client

Int32 — p_operation Operation code (op_batch_create — 99) Int32 — p_batch_statement Statement handle Buffer — p_batch_blr Row BLR of batch parameters in p_batch_dataofSend messages UInt32 — p_batch_msglen Message length Buffer — p_batch_pb Batch parameters buffer Ifptype_lazy or higher, flushing and response processing can be deferred.

Server

Generic response

11.2. Send messages

Client

Int32 — p_operation Operation code (op_batch_msg — 100) Int32 — p_batch_statement Statement handle UInt32 — p_batch_messages Number of messages Byte[] — p_batch_data Batched values (row data repeats p_batch_messages times). The length of each row data follows from the row BLR in p_batch_blr of the batch create message. Each row data must be padded to a multiple of 4:

<row-data 0>
<0-3 bytes padding> (1)
<row-data 1>
<0-3 bytes padding> (1)
...
<row-data N>
<0-3 bytes padding> (1)

1	Padding depends on the actual length of the preceding row data. Generally, the row data should already be a multiple of 4 due to its internal padding, so possibly this is an interpretation error or reverse-engineering mistake on our side.

Int32 — p_operation Operation code (op_batch_set_bpb — 106) Int32 — p_batch_statement Statement handle Buffer — p_batch_blob_bpb Default BLOB parameter buffer

Server

Generic response

11.8. Register existing blob

Client

Int32 — p_operation Operation code (op_batch_regblob — 104) Int32 — p_batch_statement Statement handle Int64 — p_batch_exist_id Existing BLOB ID Int64 — p_batch_blob_id Batch temporary BLOB ID

Server

Generic response

11.9. Stream of BLOB data

This description needs further verification and possibly correction. For example, it seems to mix up Buffer and Byte[]. We’re also not able to match some fields to the implementation. For example, the repeated "Record length" seems to be absent, or may actually refer to the p_batch_blob_data buffer length.

Client

Int32 — p_operation Operation code (op_batch_blob_stream) Int32 — p_batch_statement Statement handle Buffer[] — p_batch_blob_data BLOB stream This stream is a sequence of blob records. Each blob records contains: UInt32 Record length The following three fields are called BLOB header Int64 Batch temporary BLOB ID UInt32 BLOB size UInt32 BLOB parameters buffer size Buffer BLOB parameters buffer Buffer BLOB data (length - BLOB size bytes) (what does this mean?) BLOB headers and records in a stream need not match, i.e. one record may contain many BLOBs and BLOB may stretch from one record to next.

Server

Generic response

11.10. Batch information request

Uses the Generic information request message with:

`p_operation`	`op_info_batch` — `111`
`p_info_object`	Statement handle
`p_info_items`	Values of `INF_` constants of `IBatch` (in`IdlFbInterfaces.h`)

12. Services

This is part of the sockaddr_in structure.

It is not in XDR format

Int16 Socket family (can be ignored) Int16 Aux connection port Remaining bytes To be ignored: always use the hostname or IP address of the original connection. After a successful response, the client needs to create a connection to the specified port (the “aux connection” or auxiliary connection). The server uses this aux connection for asynchronous notification of events.

13.2. Queue events

Each queued event is notified at most once. After notification, the event needs to be requeued if the client is still interested. If a queued event was not notified, but the client is no longer interested, it can be cancelled. Notification of the queued events happens on the aux connection. See Event notification for further details.

Client

Must be sent on the main (database) connection. Int32 — p_operation Operation code (op_que_events — 48) Int32 — p_event_database Unused, always use 0 Buffer — p_event_items Event parameter buffer Byte Version (EPB_version1 — 1) The following fields are dependent on the version tag. Byte Length of event name Byte[] Event name Int32 (little-endian) Current known event count (0 when first queueing, for requeueing use the count of the previous notification) Int32 — p_event_ast Unused, always set 0 Int32 — p_event_arg Unused, always set 0 Int32 — p_event_rid Local event id — generated by the client

Server

Generic response

13.3. Cancel events

Client

Must be sent on the main (database) connection. Int32 — p_operation Operation code (op_cancel_events — 49) Int32 — p_event_database Unused, always use 0 Int32 — p_event_rid Local event id — same id as used to queue the event

Server

Generic response

13.4. Event notification

Event notification happens on the aux connection. Int32 — p_operation Operation code (op_event — 52) Int32 — p_event_database Unused, always 0 Buffer — p_event_items Event data Byte Version tag (EPB_version1 — 1) The following fields are dependent on the version tag. Byte Length of event name Byte[] Name of the event Int32 (little-endian) Event count Int32 — p_event_ast Unused Int32 — p_event_arg Unused Int32 — p_event_rid Local event id — same id as used to queue the event

14. Reading and writing row data

For sending rows (on execute) and receiving rows (on execute (op_execute2/op_exec_immediate2) or fetch), there are two things the client needs: The Row BLR (Binary Language Representation) The client only needs to write row BLR, it does not need to read it. The actual row data of a single row (or parameter) The client needs to read and write row data.

14.1. Row BLR (Binary Language Representation)

The row BLR is a description of how the client will send row data with parameters, or expects the server to send the row data. This BLR does not need to be identical to the isc_info_sql_selectorisc_info_sql_bind description, but if you use other types, they must be convertible, and for parameters, lengths can only be shorter than the length of the target type (or at least, longer lengths will result in a string truncation error if the actual value is longer). On the other hand, for output rows, describing a shorter length may result in truncation error if the actual value is longer. This can, for example, be used to let the user use a different datatype, and offload the conversion to the target datatype to the server. For CHAR/BINARY parameters, it can make sense — to reduce the transfer size — to send parameter values with their actual length, i.e. without padding with space (0x20) for non-binary, or NUL (0x00) for binary (including CHAR(n) CHARACTER SET OCTETS). However, special care must be taken for multibyte character sets like UTF8. The row BLR needs to be sent for: Execute statement for parameters: in p_sqldata_blr (if there are no parameters, an empty buffer suffices) for output row (op_execute2): in p_sqldata_out_blr op_exec_immediate2 (not yet documented) Fetch and Fetch scroll: in p_sqldata_blr The row BLR only needs to be sent for the first fetch after an execute. If sent on subsequent fetch, the server will ignore it (so changing the BLR between fetches has no effect). Create batch: in p_batch_blr Describes the parameter row values added to the batch using Send messages.

14.1.1. Row BLR format

We’ll describe the row format in terms of its envelope, individual parameters, and their types. Unless explicitly specified, values are 1 byte. The values of the blr_* constants can be found in blr.h (in[src/]include/firebird/impl/).

Envelope

{ blr_version5 | blr_version4 } (1)
blr_begin
blr_message
0 (2)
<parameter-count> (Int16 litle endian)
sequence of <parameter-description> (3)
blr_end
blr_eoc

1	Use `blr_version5` for dialect 3, use `blr_version4` for dialect 1.
2	We’re not sure of the meaning; possibly related to the value of `p_sqldata_message_number`/`p_sqldata_out_message_number`.
3	See Parameter description

Parameter description

<type-description> (1)
blr_short (2)
0 (3)

1	See Type description
2	Null indicator
3	We’re not sure, possibly “end of parameter”?

Type description

The SQL_* constants used below are defined in sqlda_pub.h (in[src/]include/firebird/impl/). These are the type values reported by isc_info_sql_type for the bind descriptions, with the nullable-bit cleared (i.e. type-value & ~1).

Simple types

For most types, the type description is a single byte:

<blr-type-code>

Where blr-type-code is one of:

`blr_double`	`SQL_DOUBLE` (`DOUBLE PRECISION`)
`blr_float`	`SQL_FLOAT` (`FLOAT`)
`blr_d_float`	`SQL_D_FLOAT` (internal double precision type, not expected to surface in practice)
`blr_sql_date`	`SQL_TYPE_DATE` (`DATE`) Not valid in dialect 1 (`blr_version4`)
`blr_sql_time`	`SQL_TYPE_TIME` (`TIME`) Not valid in dialect 1 (`blr_version4`)
`blr_timestamp`	`SQL_TIMESTAMP` (`TIMESTAMP` or dialect 1 `DATE`)
`blr_bool`	`SQL_BOOLEAN` (`BOOLEAN`)
`blr_dec64`	`SQL_DEC16` (`DECIMAL(16)`)
`blr_dec128`	`SQL_DEC34` (`DECIMAL(34)`)
`blr_timestamp_tz`	`SQL_TIMESTAMP_TZ` (`TIMESTAMP WITH TIME ZONE`)
`blr_sql_time_tz`	`SQL_TIME_TZ` (`TIME WITH TIME ZONE`)
`blr_ex_timestamp_tz`	`SQL_TIMESTAMP_TZ_EX` (`EXTENDED TIMESTAMP WITH TIME ZONE` — special bind-only variant of `TIMESTAMP WITH TIME ZONE` configurable with `SET BIND`or`isc_dpb_set_bind`)
`blr_ex_time_tz`	`SQL_TIME_TZ_EX` (`EXTENDED TIME WITH TIME ZONE` — special bind-only variant of `TIME WITH TIME ZONE` configurable with `SET BIND`or`isc_dpb_set_bind`)

Fixed point numerical types

The fixed point numerical data types (including their parent integer types) are described as:

<blr-type-code>
<scale>

Where scaleis0 for integer types or NUMERIC(p[,s])/DECIMAL(p[,s]) with sabsent or s = 0. For non-zero s, scaleis-s. This is the value reported for isc_info_sql_scale. Where blr-type-code is one of:

`blr_short`	`SQL_SHORT` (`SMALLINT`, or `NUMERIC(p[,s])` with `1 <= p <= 4`)
`blr_long`	`SQL_LONG` (`INTEGER`, `NUMERIC(p[,s])` with `4 < p <= 9`, or `DECIMAL(p[,s])` with `1 < p <= 9`)
`blr_int64`	`SQL_INT64` (`BIGINT`, or `NUMERIC(p[,s])`/`DECIMAL(p[,s])` with `9 < p <= 18`)
`blr_int128`	`SQL_INT128` (`INT128`, or `NUMERIC(p[,s])`/`DECIMAL(p[,s])` with `18 < p <= 38`)

Character/binary string types

The current way to generate BLR for character/binary string types is:

<blr-type-code>
<character-set-id> (1) (2)
<collation-id>     (1) (3)
<length> (Int16 little-endian) (4)

1	An alternative interpretation, instead of 1 byte character-set-id and 1 byte collation-id, is an Int16 little-endian with the value reported for `isc_info_sql_sub_type` (which for character/binary string types happens to be the character set id and collation id).
2	As far as we’re aware, you can also use this to specify a different character set than the character set of the target/source type, and the server will convert for you. You may need to adjust length accordingly if these character sets have different bytes per character. We haven’t verified if this actually works, so test it first.
3	The collation-id might be ignored by the server, or alternatively it might be advisable to set to `0` (e.g Jaybird does this), we’re not entirely sure about this.
4	For `blr_varying2` this is the maximum length in bytes (excluding the length prefix). For `blr_text2` this is the actual length. For variable-length encodings like UTF8, Firebird performs calculations with the maximum bytes per character value (so`CHAR(n)` in UTF8 has a length of `4 * N`).

Where blr-type-code is one of:

`blr_varying2`	`SQL_VARYING` (`VARCHAR`/`VARBINARY`)
`blr_text2`	`SQL_TEXT` (`CHAR`/`BINARY`)

As far as we know, all Firebird versions should support this encoding. An alternative — “legacy” — encoding is:

<blr-type-code>
<length> (Int16 little-endian)

Where blr-type-code is one of:

`blr_varying`	`SQL_VARYING` (`VARCHAR`/`VARBINARY`)
`blr_text`	`SQL_TEXT` (`CHAR`/`BINARY`)

Blob types

Used for SQL_BLOB. This type description only applies to Firebird 2.5 and higher. When connecting to an older Firebird version, use the type description of Array types.

blr_blob2
<subtype> (Int16 little-endian)
<character-set-id> (1) (2)
<collation-id>     (1) (3)

1	An alternative interpretation, instead of 1 byte character-set-id and 1 byte collation-id, is an Int16 little-endian with the value reported for `isc_info_sql_scale` (which for `BLOB SUB_TYPE TEXT` happens to be the character set id and collation id).
2	As far as we’re aware, you can also use this to specify a different character set than the character set of the target/source type, and the server will convert for you. You may need to adjust length accordingly if these character sets have different bytes per character. We haven’t verified if this actually works, so test it first.
3	The collation-id might be ignored by the server, or alternatively it might be advisable to set to `0` (e.g Jaybird does this), we’re not entirely sure about this.

Array types

This is used for arrays (either SQL_QUADorSQL_ARRAY), and for blobs (SQL_BLOB) with Firebird 2.1 and earlier.

blr_quad
<scale> (1)

1	The value reported for `isc_info_sql_scale` (?meaning unclear?). Firebird code sometimes sets scaleto`0` for `SQL_ARRAY` and `SQL_BLOB`.

Null type

The null type, SQL_NULL, is only used for parameters (e.g. ? IS [NOT] NULL). As far as we know, you could use any type, but the following description as a CHAR(0) is the most efficient, because you’ll send no data at all, and only an Int16 null-indicator in protocol 10 - 12 or a single bit in the null-bitset in protocol 13 and higher.

blr_text
0
0

14.2. Row data format

The format of the row data is determined by the row BLR the client sent to the server. We describe the format below in terms of the blr_* type codes, to tie it in with the BLR. In Firebird sources, reading/writing of row data is associated dtype_* values of dsc_pub.h (in[sql/]include/firebird/impl) instead; although there is not always a one-to-one correspondence between the blr_* and dtype_* names, they are generally close enough to be matched easily Numeric values are encoded in big-endian (or network-order), due to the use of arch_generic as the architecture type of the connection (see also Identification (connect)). Given how the protocol evolved, we will first show the format for protocol 10 to 12 and the format for protocol 13 and higher, and then cover the encoding of individual datatypes.

14.2.1. Row data outline

Outline for protocol 10 - 12

For protocol 10 to 12, the row is sent as:

sequence of <column-data>

Where column-data is:

<column-value>   (1) (2)
<null-indicator> (Int32) (3)

1	See Row data column value.
2	Even if the value is null, a `Byte[]` (e.g. all `0x00`) of the correct size must be written for the BLR description. In the case of `blr_varying`/`blr_varying2` a zero-length `Buffer` can be used (i.e. only an `Int32` with value `0`).
3	`0` for non-null, `-1` for null

Outline for protocol 13 and higher

For protocol 13 and higher, the row is sent as:

<null-bitset> (1) (2)
sequence of non-null <column-value> (3)

1	The bitset is a `Byte[]` of length `(column-count + 7) / 8`, padded to a multiple of 4 (i.e. similar to a `Buffer`, but without the length prefixed). When a column is null, its bit must be set, if it is non-null, its bit must be cleared (not set).
2	The encoding of the bitset is little-endian, this means the first column is the lowest bit of the first byte, or, if column n is null, `(bytes[n/8] & (1<<(n%8))) != 0`.
3	See Row data column value.

In the protocol 13 row data format, only non-null columns are sent. This means that columns that have their null bit set should be skipped (i.e. not written or read).

14.2.2. Row data column value

The following table describes how columns values must be encoded for their blr_* type.

BLR type Encoded form Remarks

BLR type	Encoded form	Remarks
`blr_text blr_text2`	`Byte[]`oflength padded to a multiple of 4	Value must be padded to length with 0x20 (space) for non-binary or 0x00 (NUL) for binary. The padding to a multiple of 4 should use the same padding character (?possibly can always be 0x00?). For UTF8, a value is `length / 4` characters long, excess bytes are set to 0x20 (space). For example, a `CHAR(10)` with 10x `a` is encoded as 10x 0x61 followed by 30x 0x20 for a length of 40! For UNICODE_FSS, a value is `length / 3` characters long, but Firebird 3.0 and older allow more characters, as long as they fit in length. Iflengthis`0`, like for `SQL_NULL` as described in Null type, then no data is sent.
`blr_varying blr_varying2`	`Buffer` with the actual encoded form, with a maximum length of length	Contrary to a normal `Buffer`, the padding of the buffer should be 0x20 (space) for non-binary and 0x00 (NUL) for binary (?possibly can always be 0x00?). For UTF8, a value is a maximum of `length / 4` characters long. For example, a `VARCHAR(10)` has a length of 40, and a value of 10x `a` is encoded as 10x 0x61, for an actual length of 10 bytes + 2 bytes of padding. For UNICODE_FSS, a value is a maximum of `length / 3` characters long, but Firebird 3.0 and older allow more characters, as long as they fit in length.
`blr_quad blr_blob2`	2x `Int32` or `Int64` or `Byte[]` with length 8	Value is the blob id
`blr_short`	`Int32` or `Byte[]` of length 4	Although `blr_short` is a 16-bit integer, it is sent as a 32-bit integer
`blr_long`	`Int32` or `Byte[]` of length 4
`blr_int64`	`Int64` or `Byte[]` of length 8
`blr_int128`	`Int128` or `Byte[]` of length 16
`blr_float`	`Byte[]` of length 4	IEEE 754 binary floating-point “single format” bit layout
`blr_double blr_d_float`	`Byte[]` of length 8	IEEE 754 binary floating-point “double format” bit layout
`blr_dec64`	`Byte[]` of length 8	IEEE-754 decimal floating point “decimal64 format” bit layout
`blr_dec128`	`Byte[]` of length 16	IEEE-754 decimal floating point “decimal128 format” bit layout
`blr_bool`	`Byte` padded to a length of 4	`1` for true, `0` for false. Alternative interpretations: a`Byte[]` of length 4, with first byte `1` for true, `0` for false An`Int32` little-endian with `1` for true, `0` for false
`blr_sql_date`	`Int32` or `Byte[]` of length 4	Not valid in dialect 1 (`blr_version4`) Integer with the number of days since 17 November 1858 (a.k.a. a Modified Julian Date).
`blr_sql_time`	`Int32` or `Byte[]` of length 4	Not valid in dialect 1 (`blr_version4`) Integer with the number of 100 microseconds (a.k.a. fractions) since midnight.
`blr_timestamp`	2x `Int32` or `Byte[]` of length 8	`Int32` date (see also `blr_sql_date`) `Int32` time (see also `blr_sql_time`)
`blr_sql_time_tz`	2x `Int32` or `Byte[]` of length 8	`Int32` time in UTC (see also `blr_sql_time`) `Int32` time zone value (offset or time zone id) See also Time zone values
`blr_timestamp_tz`	3x `Int32` or `Byte[]` of length 12	`Int32` date in UTC (see also `blr_sql_date`) `Int32` time in UTC (see also `blr_sql_time`) `Int32` time zone value (offset or time zone id) See also Time zone values
`blr_ex_time_tz`	3x `Int32` or `Byte[]` of length 12	`Int32` time in UTC (see also `blr_sql_time`) `Int32` time zone value (offset or time zone id) `Int32` offset value See also Time zone values
`blr_ex_timestamp_tz`	4x `Int32` or `Byte[]` of length 16	`Int32` date in UTC (see also `blr_sql_date`) `Int32` time in UTC (see also `blr_sql_time`) `Int32` time zone value (offset or time zone id) `Int32` offset value See also Time zone values

blr_text blr_text2

Byte[]oflength padded to a multiple of 4

Value must be padded to length with 0x20 (space) for non-binary or 0x00 (NUL) for binary. The padding to a multiple of 4 should use the same padding character (?possibly can always be 0x00?).

For UTF8, a value is length / 4 characters long, excess bytes are set to 0x20 (space). For example, a CHAR(10) with 10x a is encoded as 10x 0x61 followed by 30x 0x20 for a length of 40!

For UNICODE_FSS, a value is length / 3 characters long, but Firebird 3.0 and older allow more characters, as long as they fit in length.

Iflengthis0, like for SQL_NULL as described in Null type, then no data is sent.

blr_varying blr_varying2

Buffer with the actual encoded form, with a maximum length of length

Contrary to a normal Buffer, the padding of the buffer should be 0x20 (space) for non-binary and 0x00 (NUL) for binary (?possibly can always be 0x00?).

For UTF8, a value is a maximum of length / 4 characters long. For example, a VARCHAR(10) has a length of 40, and a value of 10x a is encoded as 10x 0x61, for an actual length of 10 bytes + 2 bytes of padding.

For UNICODE_FSS, a value is a maximum of length / 3 characters long, but Firebird 3.0 and older allow more characters, as long as they fit in length.

blr_quad blr_blob2

2x Int32
or Int64
or Byte[] with length 8

Value is the blob id

blr_short

Int32
or Byte[] of length 4

Although blr_short is a 16-bit integer, it is sent as a 32-bit integer

blr_long

Int32
or Byte[] of length 4

blr_int64

Int64
or Byte[] of length 8

blr_int128

Int128
or Byte[] of length 16

blr_float

Byte[] of length 4

IEEE 754 binary floating-point “single format” bit layout

blr_double blr_d_float

Byte[] of length 8

IEEE 754 binary floating-point “double format” bit layout

blr_dec64

Byte[] of length 8

IEEE-754 decimal floating point “decimal64 format” bit layout

blr_dec128

Byte[] of length 16

IEEE-754 decimal floating point “decimal128 format” bit layout

blr_bool

Byte padded to a length of 4

1 for true, 0 for false.

Alternative interpretations:

aByte[] of length 4, with first byte 1 for true, 0 for false

AnInt32 little-endian with 1 for true, 0 for false

blr_sql_date

Int32
or Byte[] of length 4

Not valid in dialect 1 (blr_version4)

Integer with the number of days since 17 November 1858 (a.k.a. a Modified Julian Date).

blr_sql_time

Int32
or Byte[] of length 4

Not valid in dialect 1 (blr_version4)

Integer with the number of 100 microseconds (a.k.a. fractions) since midnight.

blr_timestamp

2x Int32
or Byte[] of length 8

Int32

date (see also blr_sql_date)

Int32

time (see also blr_sql_time)

blr_sql_time_tz

2x Int32
or Byte[] of length 8

Int32

time in UTC (see also blr_sql_time)

Int32

time zone value (offset or time zone id)

See also Time zone values

blr_timestamp_tz

3x Int32
or Byte[] of length 12

Int32

date in UTC (see also blr_sql_date)

Int32

time in UTC (see also blr_sql_time)

Int32

time zone value (offset or time zone id)

See also Time zone values

blr_ex_time_tz

3x Int32
or Byte[] of length 12

Int32

time in UTC (see also blr_sql_time)

Int32

time zone value (offset or time zone id)

Int32

offset value

See also Time zone values

blr_ex_timestamp_tz

4x Int32
or Byte[] of length 16

Int32

date in UTC (see also blr_sql_date)

Int32

time in UTC (see also blr_sql_time)

Int32

time zone value (offset or time zone id)

Int32

offset value

See also Time zone values

Time zone values

The time zone value is an unsigned 16-bit integer encoded as an Int32, containing either an offset value or a time zone id. The “extended” time zone types (blr_ex_time_tz/blr_ex_timestamp_tz), have a second time zone value that is always an offset. This value can be used when you don’t want to derive offsets for named zones yourself. When sending values to the server, this second value can be set to 0, as the server always uses the first time zone value. If the value is between 0 and 2878, it is an offset. You can get the actual offset in minutes with value - 1439, making the range [-1439,+1439], or [-23:59,+23:59]. Be aware that in practice, offsets have a smaller range. If the author recalls correctly, the normal range is something like [-12:00,+14:00]. Time zone libraries may also have their own limits, for example Java’s java.time.ZoneOffset only allows [-18:00, +18:00] or [-1080,+1080]. We recommend treating values that are out of range of your time zone library as offset +00:00 (i.e. UTC/GMT). If the value is greater than 2878 (up to 65535, or GMT) it is a time zone id (i.e. (2878,65535]). The actual range — for Firebird 5.0.2 — is [64899,65535] (ids are assigned downwards from 65535). The time zone ids can be mapped to a time zone name using the RDB$TIME_ZONES table. New Firebird releases (or possibly ICU time zone data updates) may introduce new time zone ids, but existing ids should be stable. We recommend keeping your own list instead of querying RDB$TIME_ZONES. Depending on your time zone library, it may be necessary to “fix” or correct the mapping, for example by using a different name for the same zone, or to even use UTC or GMT if the zone is unknown to your time zone library. As an example, 65034 is listed with name Factory which seems to be ICU specific (?), but is the same as GMT.

Appendix A: External Data Representation (XDR)

The Firebird wire protocol uses XDR for exchange of messages between client and server. The encoding of integers is big-endian (network order). However, some data inside the messages may be little-endian (also known as VAX encoding within Firebird sources).

Appendix B: Data types

Int32 Integer 32-bits In some cases — e.g. object handles, and some lengths — this is actually a 16-bit “short” encoded as a 32-bit integer with the high bits zero. Whether the number should be interpreted as signed or unsigned may depend on the context; when we are sure it’s unsigned, we’ll generally specify UInt32 documented next. UInt32 Unsigned integer 32-bits Int64 Integer 64-bits Alternatively, especially for blob and arrays ids, can be interpreted as two Int32, a.k.a. a “quad”. Interpretation as a 64-bit integer — even for blob and array ids — is generally simpler, and should not make a difference. Whether the number should be interpreted as signed or unsigned may depend on the context. Buffer Composed of Int32 Length of buffer data without padding Byte[] Buffer data Byte[] Padding of 0 to 3 bytes to align the message to a multiple of 4 (e.g. calculated as (4 - length) &3)). That is, for some N >= 0, when the buffer length is: N * 4 bytes → no padding N * 4 + 1 bytes → 3 bytes padding N * 4 + 2 bytes → 2 bytes padding N * 4 + 3 bytes → 1 byte padding Byte[] An array of bytes Length follows from another field in the message, from correct parsing of the value, or from other specifics of the message. String A text string, read or written as a Buffer, encoded in the connection character set or some message or context specific character set

Appendix C: Revision history

Revision History

Revision History
0.18	18 May 2025	MR	Documented `op_inline_blob` (protocol 19) and updated execute and fetch documentation Documented `op_fetch_scroll` (protocol 18) Documented `op_info_cursor` (protocol 18) Documented row BLR format Documented row data format
0.17	17 May 2025	MR	Reordered revision history, so latest change is at the top Documented `op_dummy` Documented `op_event` Documented `op_exit`/`op_disconnect` on aux connection Documented `op_reconnect` Improved protocol 11 descriptions Documented protocol 12 (`op_cancel`) Documented the value next to the constant names Partially documented protocol 11 `op_trusted_auth` (message, not logic) Documented protocol 13 connect/authentication/attach: `op_accept_data`, `op_cond_accept`, `op_cont_auth`, `op_crypt_key_callback`, `op_crypt`, authentication and attach flow Described info request message in one place
0.16	13 Apr 2025	MR	Added Firebird struct field names to message descriptions for reference Updated, corrected and expanded field descriptions Documented `op_put_segment` Added missing field in `p_sgmt_length`in`op_batch_segments` Documented protocol 11 batching of operations for blobs Documented protocol 16 timeout (`p_sqldata_timeout`) for `op_execute`/`op_execute2` Documented protocol 18 cursor flags (`p_sqldata_cursor_flags`) for `op_execute`/`op_execute2` Documented protocol 19 inline blob size (`p_sqldata_inline_blob_size`) for `op_execute`/`op_execute2` (but not yet `op_inline_blob`!)
0.15	26 Dec 2021	AP	Document batch execution
0.14	04 Aug 2020	MR	Conversion to AsciiDoc, minor copy-editing
0.13	13 Sep 2014		Updated and expanded protocol information
0.12	21 Jun 2004		Updated services information.
0.11	20 Jun 2004		Added new segmentedlist. Updated Statements.Prepare documentation. Updated Statements.Execute documentation. Updated Blobs.GetSegment documentation. Updated Blobs.Seek documentation.
0.10	19 Jun 2004		Changed rendering of important tags using Paul Vinkenoog fix.
0.9	18 Jun 2004		Improved segmentedlist usage. Fixed rendering of important tags.
0.8	17 Jun 2004		Added two new segmented lists.
0.7	16 Jun 2004		Modified document ID to wireprotocol.
0.6	07 Jun 2004		Added events system documentation.
0.5	06 Jun 2004		Fixed issues reported by Paul Vinkenoog.
0.4	05 Jun 2004		Fixed issues reported by Paul Vinkenoog.
0.3	03 Jun 2004		Added new subsections to the Statements section.
0.2	02 Jun 2004		Fixed issues reported by Paul Vinkenoog.
0.1	31 May 2004		First draft for review.

0.18

18 May 2025

Documented op_inline_blob (protocol 19) and updated execute and fetch documentation

Documented op_fetch_scroll (protocol 18)

Documented op_info_cursor (protocol 18)

Documented row BLR format

Documented row data format

0.17

17 May 2025

Reordered revision history, so latest change is at the top

Documented op_dummy

Documented op_event

Documented op_exit/op_disconnect on aux connection

Documented op_reconnect

Improved protocol 11 descriptions

Documented protocol 12 (op_cancel)

Documented the value next to the constant names

Partially documented protocol 11 op_trusted_auth (message, not logic)

Documented protocol 13 connect/authentication/attach: op_accept_data, op_cond_accept, op_cont_auth, op_crypt_key_callback, op_crypt, authentication and attach flow

Described info request message in one place

0.16

13 Apr 2025

Added Firebird struct field names to message descriptions for reference

Updated, corrected and expanded field descriptions

Documented op_put_segment

Added missing field in p_sgmt_lengthinop_batch_segments

Documented protocol 11 batching of operations for blobs

Documented protocol 16 timeout (p_sqldata_timeout) for op_execute/op_execute2

Documented protocol 18 cursor flags (p_sqldata_cursor_flags) for op_execute/op_execute2

Documented protocol 19 inline blob size (p_sqldata_inline_blob_size) for op_execute/op_execute2 (but not yet op_inline_blob!)

0.15

26 Dec 2021

Document batch execution

0.14

04 Aug 2020

Conversion to AsciiDoc, minor copy-editing

0.13

13 Sep 2014

Updated and expanded protocol information

0.12

21 Jun 2004

Updated services information.

0.11

20 Jun 2004

Added new segmentedlist.

Updated Statements.Prepare documentation.

Updated Statements.Execute documentation.

Updated Blobs.GetSegment documentation.

Updated Blobs.Seek documentation.

0.10

19 Jun 2004

Changed rendering of important tags using Paul Vinkenoog fix.

0.9

18 Jun 2004

Improved segmentedlist usage.

Fixed rendering of important tags.

0.8

17 Jun 2004

Added two new segmented lists.

0.7

16 Jun 2004

Modified document ID to wireprotocol.

0.6

07 Jun 2004

Added events system documentation.

0.5

06 Jun 2004

Fixed issues reported by Paul Vinkenoog.

0.4

05 Jun 2004

Fixed issues reported by Paul Vinkenoog.

0.3

03 Jun 2004

Added new subsections to the Statements section.

0.2

02 Jun 2004

Fixed issues reported by Paul Vinkenoog.

0.1

31 May 2004

First draft for review.

1. This is not required, at least not in recent Firebird versions. The server handles the end of the buffer without seeing isc_info_end as an implicit isc_info_end. However, we’re not sure if that was always the case, so for potential compatibility reasons, consider it “required” Version 0.18 Last updated 2025-05-18 19:25:37 +0200

Firebird Wire Protocol

1. Introduction

2. Protocol versions

2.1. Protocol 10

2.2. Protocol 11

2.3. Protocol 12

2.4. Protocol 13

2.5. Protocol 14

2.6. Protocol 15

2.7. Protocol 16

2.8. Protocol 17

2.9. Protocol 18

2.10. Protocol 19

3. Common responses

3.1. Generic response

3.2. SQL response

3.3. Fetch response

3.4. Inline blob response

3.5. Slice response

3.6. Dummy response

3.7. Exit or disconnect command (aux connection)

4. Common requests

4.1. Generic information request

Client

Server

5. Establishing connection

5.1. Attaching to a database or service

5.2. Identification (connect)

5.3. Simple accept

5.4. Accept with data orconditional accept

5.5. Continue authentication

5.6. Trusted authentication

5.7. Database encryption key callback

Additions in protocol 14

5.8. Enable wire encryption

Client

Server

5.9. Attachment to database or service

Client

Server

5.10. Connection rejection

5.11. Connection handshake

5.11.1. Protocol 10 — 12

5.11.2. Protocol 13 and higher

5.12. Detach

Client

Server

5.13. Disconnect

Client

Server

6. Databases

6.1. Attach database

6.2. Create database

The CREATE DATABASE statement

6.3. Drop

Client

Server

6.4. Detach and disconnect

6.5. Database information request

6.6. Cancellation

Client

Server

7. Transactions

7.1. Start transaction

Client

Server

The SET TRANSACTION statement

7.1.1. Deviations for protocol version 11

7.2. Commit transaction

Client

Server

7.3. Rollback transaction

Client

Server

7.4. Commit retaining

Client

Server

7.5. Rollback retaining

Client

Server

The `CREATE DATABASE` statement

The `SET TRANSACTION` statement