TIDB_TRX can not parse CURRENT_SQL_DIGEST_TEXT where use two tidb

[vivid392845427]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

drop table if exists t;
create table t (a int primary key, b int);
insert into t values (1, 10), (2, 20), (3, 30);
/* tidb0 / begin;
/ tidb0 / update t set b=11 where a =1;
/ tidb1 session1*/ update t set b=12 where a =1; ---block
/* tidb1 session2*/ select * from TIDB_TRX\G ---check result

2. What did you expect to see? (Required)

parse CURRENT_SQL_DIGEST and CURRENT_SQL_DIGEST_TEXT correctly;

3. What did you see instead (Required)

parse CURRENT_SQL_DIGEST correctly, but CURRENT_SQL_DIGEST_TEXT is null,as follow:

mysql> select * from TIDB_TRX\G
*************************** 1. row ***************************
ID: 426921474408841217
START_TIME: 2021-08-10 06:16:21.064000
CURRENT_SQL_DIGEST: 3b491f15bc52ff182a37547ba0ccb3103f658e6d7935303836017fbf5cc0c75c
CURRENT_SQL_DIGEST_TEXT: NULL
STATE: Committing
WAITING_START_TIME: NULL
MEM_BUFFER_KEYS: 1
MEM_BUFFER_BYTES: 29
SESSION_ID: 7
USER: root
DB: test
ALL_SQL_DIGESTS: ["3b491f15bc52ff182a37547ba0ccb3103f658e6d7935303836017fbf5cc0c75c"]
1 row in set (0.00 sec)

4. What is your TiDB version? (Required)

Release Version: v5.2.0-alpha-562-ge539f9d62
Edition: Community
Git Commit Hash: e539f9d
Git Branch: master
UTC Build Time: 2021-08-09 11:35:07
GoVersion: go1.16.4
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false

[MyonKeminta]

This is an expected behavior on our current implementation.

• information_schema.tidb_trx internally uses statements_summary and statements_summary_history tables to retrieve the current_sql_digest_text information, so it only access only the current TIDB node to retrieve current_sql_digest_text information. cluster_statements_summary and cluster_statements_summary_history is not used, in order to reduce the overhead.
• Currently, only statements that has been finished will be collected to statement summary tables.

So in this case, the tidb1 executes the statement "update t set b=12 where a =1;" for the first time and has not yet finished. At this time, it's expected that we cannot get the SQL digest text on this node.

[jebter]

The issue has not been updated for too long, so I will close it. If there are any updates, you can reopen it.