mysql-compatibility: correct performance_schema statement

[dveeden]

What is changed, added or deleted? (Required)

The session_connect_attrs table is not empty and the pd%, tidb% and tikv% tables are also not empty.

mysql-8.0.11-TiDB-v8.5.0> SELECT * FROM performance_schema.session_connect_attrs;
+----------------+-----------------+------------+------------------+
| PROCESSLIST_ID | ATTR_NAME       | ATTR_VALUE | ORDINAL_POSITION |
+----------------+-----------------+------------+------------------+
|     2376073220 | _client_name    | libmysql   |                0 |
|     2376073220 | _client_version | 9.1.0      |                1 |
|     2376073220 | _os             | Linux      |                2 |
|     2376073220 | _pid            | 2987910    |                3 |
|     2376073220 | _platform       | x86_64     |                4 |
|     2376073220 | os_user         | dvaneeden  |                5 |
|     2376073220 | program_name    | mysql      |                6 |
+----------------+-----------------+------------+------------------+
7 rows in set (0.00 sec)

mysql-8.0.11-TiDB-v8.5.0>

• https://docs.pingcap.com/tidb/stable/performance-schema

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• v8.3 (TiDB 8.3 versions)
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• v5.3 (TiDB 5.3 versions)

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[lilin90]

Does this update also apply to the custom content for TiDB Cloud?

[dveeden]

Yes.

mysql-5.7.28-TiDB-Serverless> TABLE performance_schema.session_variables LIMIT 5;
+-----------------------------------+----------------+
| VARIABLE_NAME                     | VARIABLE_VALUE |
+-----------------------------------+----------------+
| innodb_io_capacity_max            | 2000           |
| tidb_non_prepared_plan_cache_size | 100            |
| version_compile_os                | linux          |
| net_retry_count                   | 10             |
| tidb_current_ts                   | 0              |
+-----------------------------------+----------------+
5 rows in set (0.04 sec)

mysql-5.7.28-TiDB-Serverless> SELECT TIDB_VERSION()\G
*************************** 1. row ***************************
TIDB_VERSION(): Release Version: v7.1.3-serverless
Edition: Community
Git Commit Hash: 2e8be50b073c26b8979c6988a3888ce57b5cec99
Git Branch: release-7.1-serverless
UTC Build Time: 2024-11-22 15:30:17
GoVersion: go1.21.11
Race Enabled: false
TiKV Min Version: 6.1.0
Check Table Before Drop: false
Store: tikv
1 row in set (0.02 sec)

So performance_schema.session_variables is not empty.

performance_schema.session_connect_attrs doesn't exist on TiDB Cloud Serverless, which is because v7.1.3 doesn't yet have this table. TiDB v7.5 does have this table.

[dveeden]

Looks like session_variables was introduced in v6.2.0

[dveeden]

On TiDB Cloud Serverless this is the only table with data.

$ mysqldump -u '4BFMphWRTf5tr4V.root' -h gateway01.eu-central-1.prod.aws.tidbcloud.com -P 4000 -pXXXXXXXXXX --skip-lock-tables --no-create-info performance_schema | awk '/^INSERT/ { print substr($0,0,100) }'
mysqldump: [Warning] Using a password on the command line interface can be insecure.
-- Warning: column statistics not supported by the server.
INSERT INTO `session_variables` VALUES ('tidb_build_stats_concurrency','4'),('tidb_opt_skew_distinct

On TiDB Cloud Dedicated there are most likely more.

[lilin90]

@dveeden Then it seems that we also need to update line 146? Performance schema tables return empty results in TiDB.

[dveeden]

@lilin90 correct. I've pushed a commit to update that line.

[lilin90]

/lgtm

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-01-10 06:42:17.14348674 +0000 UTC m=+508680.432318445: ☑️ agreed by lilin90.

[lilin90]

/approve

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.5: #19955.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #19956.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.1: #19957.