From 588cac61f196f8df2235ab8a6b0ec921f96bf63c Mon Sep 17 00:00:00 2001 From: jiong-nba <2301210292@stu.pku.edu.cn> Date: Tue, 10 Mar 2026 10:57:19 +0800 Subject: [PATCH 1/3] docs: sync session connect attrs docs with tidb#66617 --- .../information-schema-slow-query.md | 6 ++++-- .../performance-schema-session-connect-attrs.md | 12 ++++++++++++ status-variables.md | 12 ++++++++++++ system-variable-reference.md | 7 +++++++ system-variables.md | 17 +++++++++++++++++ 5 files changed, 52 insertions(+), 2 deletions(-) diff --git a/information-schema/information-schema-slow-query.md b/information-schema/information-schema-slow-query.md index 7413fa8b46356..b19224c833ed6 100644 --- a/information-schema/information-schema-slow-query.md +++ b/information-schema/information-schema-slow-query.md @@ -126,9 +126,10 @@ The output is as follows: | Plan_digest | varchar(128) | YES | | NULL | | | Binary_plan | longtext | YES | | NULL | | | Prev_stmt | longtext | YES | | NULL | | +| Session_connect_attrs | json | YES | | NULL | | | Query | longtext | YES | | NULL | | +--------------------------------------------+-----------------+------+------+---------+-------+ -89 rows in set (0.00 sec) +90 rows in set (0.00 sec) ``` The maximum statement length of the `Query` column is limited by the [`tidb_stmt_summary_max_sql_length`](/system-variables.md#tidb_stmt_summary_max_sql_length-new-in-v40) system variable. @@ -246,9 +247,10 @@ The output is as follows: | Plan_digest | varchar(128) | YES | | NULL | | | Binary_plan | longtext | YES | | NULL | | | Prev_stmt | longtext | YES | | NULL | | +| Session_connect_attrs | json | YES | | NULL | | | Query | longtext | YES | | NULL | | +--------------------------------------------+-----------------+------+------+---------+-------+ -90 rows in set (0.00 sec) +91 rows in set (0.00 sec) ``` When the cluster system table is queried, TiDB does not obtain data from all nodes, but pushes down the related calculation to other nodes. The execution plan is as follows: diff --git a/performance-schema/performance-schema-session-connect-attrs.md b/performance-schema/performance-schema-session-connect-attrs.md index fabbce7e9f110..8248a0958b5fa 100644 --- a/performance-schema/performance-schema-session-connect-attrs.md +++ b/performance-schema/performance-schema-session-connect-attrs.md @@ -66,3 +66,15 @@ Fields in the `SESSION_CONNECT_ATTRS` table are described as follows: * `ATTR_NAME`: Attribute name. * `ATTR_VALUE`: Attribute value. * `ORDINAL_POSITION`: Ordinal position of the name/value pair. + +## Size limit and truncation + +TiDB uses the [`performance_schema_session_connect_attrs_size`](/system-variables.md#performance_schema_session_connect_attrs_size) global system variable to control the maximum total size of connection attributes per session. + +- Default value: `4096` bytes +- Range: `[-1, 65536]` +- `-1` means no configured limit, and TiDB treats it as up to `65536` bytes. + +When the total size exceeds this limit, TiDB truncates excess attributes and adds `_truncated` to indicate the number of truncated bytes. + +TiDB also enforces a hard limit of 1 MiB on connection attribute payload in handshake packets. If this hard limit is exceeded, the connection is rejected. diff --git a/status-variables.md b/status-variables.md index ec577d88c6173..ec07a6e52e2bf 100644 --- a/status-variables.md +++ b/status-variables.md @@ -31,6 +31,18 @@ Additionally, the [FLUSH STATUS](/sql-statements/sql-statement-flush-status.md) - Type: Integer - The compression level that is used for the MySQL Protocol. +### Performance_schema_session_connect_attrs_longest_seen + +- Scope: GLOBAL +- Type: Integer +- The largest total size (in bytes) of session connection attributes observed by TiDB. + +### Performance_schema_session_connect_attrs_lost + +- Scope: GLOBAL +- Type: Integer +- The number of sessions whose connection attributes were truncated due to `performance_schema_session_connect_attrs_size`. + ### Ssl_cipher - Scope: SESSION | GLOBAL diff --git a/system-variable-reference.md b/system-variable-reference.md index ef41aa77a6c3c..3315e086b218c 100644 --- a/system-variable-reference.md +++ b/system-variable-reference.md @@ -600,6 +600,13 @@ Referenced in: - [TiDB 8.5.0 Release Notes](/releases/release-8.5.0.md) - [TiDB 7.6.0 Release Notes](/releases/release-7.6.0.md) +### performance_schema_session_connect_attrs_size + +Referenced in: + +- [SESSION_CONNECT_ATTRS](/performance-schema/performance-schema-session-connect-attrs.md) +- [System Variables](/system-variables.md#performance_schema_session_connect_attrs_size) + ### plugin_dir Referenced in: diff --git a/system-variables.md b/system-variables.md index 79af0db79a694..9d56d900b1394 100644 --- a/system-variables.md +++ b/system-variables.md @@ -789,6 +789,23 @@ mysql> SHOW GLOBAL VARIABLES LIKE 'max_prepared_stmt_count'; 1 row in set (0.00 sec) ``` +### performance_schema_session_connect_attrs_size + +- Scope: GLOBAL +- Persists to cluster: Yes +- Applies to hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value): No +- Type: Integer +- Default value: `4096` +- Range: `[-1, 65536]` +- Unit: Bytes +- Controls the maximum total size of connection attributes for each session. +- If the total size of connection attributes exceeds this value, TiDB truncates excess attributes and adds `_truncated` to indicate the number of truncated bytes. +- The value `-1` means no configured limit and is treated as up to `65536` bytes in TiDB. + +> **Note:** +> +> TiDB enforces a hard limit of 1 MiB for handshake connection attributes. If this hard limit is exceeded, the connection is rejected. + ### pd_enable_follower_handle_region New in v7.6.0 - Scope: GLOBAL From 8f0c5181c328617cba937a4ad95293a9001f3fc4 Mon Sep 17 00:00:00 2001 From: jiong-nba <2301210292@stu.pku.edu.cn> Date: Tue, 10 Mar 2026 17:01:04 +0800 Subject: [PATCH 2/3] docs: clarify connect attrs size impact on slow log payload --- information-schema/information-schema-slow-query.md | 2 ++ performance-schema/performance-schema-session-connect-attrs.md | 2 ++ system-variables.md | 2 ++ 3 files changed, 6 insertions(+) diff --git a/information-schema/information-schema-slow-query.md b/information-schema/information-schema-slow-query.md index b19224c833ed6..82b3635fb7e56 100644 --- a/information-schema/information-schema-slow-query.md +++ b/information-schema/information-schema-slow-query.md @@ -134,6 +134,8 @@ The output is as follows: The maximum statement length of the `Query` column is limited by the [`tidb_stmt_summary_max_sql_length`](/system-variables.md#tidb_stmt_summary_max_sql_length-new-in-v40) system variable. +The `Session_connect_attrs` column stores session connection attributes in JSON format parsed from the slow log. TiDB controls the maximum payload size written to this field using [`performance_schema_session_connect_attrs_size`](/system-variables.md#performance_schema_session_connect_attrs_size). + ## CLUSTER_SLOW_QUERY table The `CLUSTER_SLOW_QUERY` table provides the slow query information of all nodes in the cluster, which is the parsing result of the TiDB slow log files. You can use the `CLUSTER_SLOW_QUERY` table the way you do with `SLOW_QUERY`. The table schema of the `CLUSTER_SLOW_QUERY` table differs from that of the `SLOW_QUERY` table in that an `INSTANCE` column is added to `CLUSTER_SLOW_QUERY`. The `INSTANCE` column represents the TiDB node address of the row information on the slow query. diff --git a/performance-schema/performance-schema-session-connect-attrs.md b/performance-schema/performance-schema-session-connect-attrs.md index 8248a0958b5fa..f4dcd14012bee 100644 --- a/performance-schema/performance-schema-session-connect-attrs.md +++ b/performance-schema/performance-schema-session-connect-attrs.md @@ -77,4 +77,6 @@ TiDB uses the [`performance_schema_session_connect_attrs_size`](/system-variable When the total size exceeds this limit, TiDB truncates excess attributes and adds `_truncated` to indicate the number of truncated bytes. +The accepted connection attributes are also written to the `Session_connect_attrs` field in the slow log and can be queried from `INFORMATION_SCHEMA.SLOW_QUERY` and `INFORMATION_SCHEMA.CLUSTER_SLOW_QUERY`. To control the payload size written to the slow log, adjust `performance_schema_session_connect_attrs_size`. + TiDB also enforces a hard limit of 1 MiB on connection attribute payload in handshake packets. If this hard limit is exceeded, the connection is rejected. diff --git a/system-variables.md b/system-variables.md index 9d56d900b1394..cef35e91b31ee 100644 --- a/system-variables.md +++ b/system-variables.md @@ -800,6 +800,8 @@ mysql> SHOW GLOBAL VARIABLES LIKE 'max_prepared_stmt_count'; - Unit: Bytes - Controls the maximum total size of connection attributes for each session. - If the total size of connection attributes exceeds this value, TiDB truncates excess attributes and adds `_truncated` to indicate the number of truncated bytes. +- Connection attributes accepted within this limit are written to the `Session_connect_attrs` field in the slow log and can be queried from [`INFORMATION_SCHEMA.SLOW_QUERY`](/information-schema/information-schema-slow-query.md) and `INFORMATION_SCHEMA.CLUSTER_SLOW_QUERY`. +- You can control the size of `Session_connect_attrs` recorded in the slow log by adjusting this variable. - The value `-1` means no configured limit and is treated as up to `65536` bytes in TiDB. > **Note:** From e005d6338e1a1b8c38b4dcd9fc5b919299d5d2a8 Mon Sep 17 00:00:00 2001 From: jiong-nba <2301210292@stu.pku.edu.cn> Date: Mon, 16 Mar 2026 11:07:56 +0800 Subject: [PATCH 3/3] docs: mark connect attrs size variable as new in v9.0.0 --- information-schema/information-schema-slow-query.md | 2 +- performance-schema/performance-schema-session-connect-attrs.md | 2 +- system-variable-reference.md | 2 +- system-variables.md | 2 +- 4 files changed, 4 insertions(+), 4 deletions(-) diff --git a/information-schema/information-schema-slow-query.md b/information-schema/information-schema-slow-query.md index 82b3635fb7e56..9b3de52791dac 100644 --- a/information-schema/information-schema-slow-query.md +++ b/information-schema/information-schema-slow-query.md @@ -134,7 +134,7 @@ The output is as follows: The maximum statement length of the `Query` column is limited by the [`tidb_stmt_summary_max_sql_length`](/system-variables.md#tidb_stmt_summary_max_sql_length-new-in-v40) system variable. -The `Session_connect_attrs` column stores session connection attributes in JSON format parsed from the slow log. TiDB controls the maximum payload size written to this field using [`performance_schema_session_connect_attrs_size`](/system-variables.md#performance_schema_session_connect_attrs_size). +The `Session_connect_attrs` column stores session connection attributes in JSON format parsed from the slow log. TiDB controls the maximum payload size written to this field using [`performance_schema_session_connect_attrs_size`](/system-variables.md#performance_schema_session_connect_attrs_size-new-in-v900). ## CLUSTER_SLOW_QUERY table diff --git a/performance-schema/performance-schema-session-connect-attrs.md b/performance-schema/performance-schema-session-connect-attrs.md index f4dcd14012bee..f6ee682eb4f4e 100644 --- a/performance-schema/performance-schema-session-connect-attrs.md +++ b/performance-schema/performance-schema-session-connect-attrs.md @@ -69,7 +69,7 @@ Fields in the `SESSION_CONNECT_ATTRS` table are described as follows: ## Size limit and truncation -TiDB uses the [`performance_schema_session_connect_attrs_size`](/system-variables.md#performance_schema_session_connect_attrs_size) global system variable to control the maximum total size of connection attributes per session. +TiDB uses the [`performance_schema_session_connect_attrs_size`](/system-variables.md#performance_schema_session_connect_attrs_size-new-in-v900) global system variable to control the maximum total size of connection attributes per session. - Default value: `4096` bytes - Range: `[-1, 65536]` diff --git a/system-variable-reference.md b/system-variable-reference.md index 3315e086b218c..d5f2db378b997 100644 --- a/system-variable-reference.md +++ b/system-variable-reference.md @@ -605,7 +605,7 @@ Referenced in: Referenced in: - [SESSION_CONNECT_ATTRS](/performance-schema/performance-schema-session-connect-attrs.md) -- [System Variables](/system-variables.md#performance_schema_session_connect_attrs_size) +- [System Variables](/system-variables.md#performance_schema_session_connect_attrs_size-new-in-v900) ### plugin_dir diff --git a/system-variables.md b/system-variables.md index cef35e91b31ee..e14b0a10012ba 100644 --- a/system-variables.md +++ b/system-variables.md @@ -789,7 +789,7 @@ mysql> SHOW GLOBAL VARIABLES LIKE 'max_prepared_stmt_count'; 1 row in set (0.00 sec) ``` -### performance_schema_session_connect_attrs_size +### performance_schema_session_connect_attrs_size New in v9.0.0 - Scope: GLOBAL - Persists to cluster: Yes