tidb_row_checksum(): Update docs

[dveeden]

What is changed, added or deleted? (Required)

1. The statement in the example had syntax errors
2. The variable docs didn't link to the function

Which TiDB version(s) do your changes apply to? (Required)

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• v8.2 (TiDB 8.2 versions)
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• v5.2 (TiDB 5.2 versions)
• v5.1 (TiDB 5.1 versions)

What is the related PR or file link(s)?

• This PR is translated from:

• Other reference link(s):

• cdc: the e2e checksum integrity check functionality #13258

• *: add tidb_row_checksum() as a builtin function tidb#43479

Do your changes match any of the following descriptions?

• Delete files
• Change aliases
• Need modification after applied to another branch
• Might cause conflicts after applied to another branch

[dveeden]

This doesn't fix all issues:

For me the example returns NULL instead of the checksum:

sql> SELECT TIDB_VERSION()\G
*************************** 1. row ***************************
TIDB_VERSION(): Release Version: v8.1.0
Edition: Community
Git Commit Hash: 945d07c5d5c7a1ae212f6013adfb187f2de24b23
Git Branch: HEAD
UTC Build Time: 2024-05-21 03:51:57
GoVersion: go1.21.10
Race Enabled: false
Check Table Before Drop: false
Store: tikv
1 row in set (0.0011 sec)

sql> SET GLOBAL tidb_enable_row_level_checksum = ON;
Query OK, 0 rows affected (0.0223 sec)

sql> USE test;
Default schema set to `test`.
Fetching global names, object names from `test` for auto-completion... Press ^C to stop.

sql> CREATE TABLE t (id INT PRIMARY KEY, k INT, c CHAR(1));
Query OK, 0 rows affected (0.1103 sec)

sql> INSERT INTO t values (1, 10, 'a');
Query OK, 1 row affected (0.0045 sec)

sql> SELECT *, TIDB_ROW_CHECKSUM() FROM t WHERE id = 1;
+----+----+---+---------------------+
| id | k  | c | TIDB_ROW_CHECKSUM() |
+----+----+---+---------------------+
|  1 | 10 | a | NULL                |
+----+----+---+---------------------+
1 row in set (0.0014 sec)

2. I don't think the "FastPlan" that is mentioned here is documented well enough.

Is "FastPlan" a generic term for PointGet and TableDual and Set?

https://github.com/pingcap/tidb/blob/df64c343ddfc4063891900acf95e2b3640c79f29/pkg/executor/adapter.go#L398-L417

[dveeden]

Looks like a re-connect is needed for this to work:

dvaneeden@dve-carbon:~$ mysqlsh mysql://root@127.0.0.1:4000/test

sql> SHOW GLOBAL VARIABLES LIKE 'tidb_enable_row_level_checksum';
+--------------------------------+-------+
| Variable_name                  | Value |
+--------------------------------+-------+
| tidb_enable_row_level_checksum | OFF   |
+--------------------------------+-------+
1 row in set (0.0009 sec)

sql> SHOW SESSION VARIABLES LIKE 'tidb_enable_row_level_checksum';
+--------------------------------+-------+
| Variable_name                  | Value |
+--------------------------------+-------+
| tidb_enable_row_level_checksum | OFF   |
+--------------------------------+-------+
1 row in set (0.0013 sec)

sql> SET GLOBAL tidb_enable_row_level_checksum = ON;
Query OK, 0 rows affected (0.0186 sec)

sql> SHOW GLOBAL VARIABLES LIKE 'tidb_enable_row_level_checksum';
+--------------------------------+-------+
| Variable_name                  | Value |
+--------------------------------+-------+
| tidb_enable_row_level_checksum | ON    |
+--------------------------------+-------+
1 row in set (0.0014 sec)

sql> SHOW SESSION VARIABLES LIKE 'tidb_enable_row_level_checksum';
+--------------------------------+-------+
| Variable_name                  | Value |
+--------------------------------+-------+
| tidb_enable_row_level_checksum | ON    |
+--------------------------------+-------+
1 row in set (0.0015 sec)

sql> USE test;
Default schema set to `test`.
Fetching global names, object names from `test` for auto-completion... Press ^C to stop.

sql> CREATE TABLE t (id INT PRIMARY KEY, k INT, c CHAR(1));
Query OK, 0 rows affected (0.1069 sec)

sql> INSERT INTO t values (1, 10, 'a');
Query OK, 1 row affected (0.0124 sec)

sql> SELECT *, TIDB_ROW_CHECKSUM() FROM t WHERE id = 1;
+----+----+---+---------------------+
| id | k  | c | TIDB_ROW_CHECKSUM() |
+----+----+---+---------------------+
|  1 | 10 | a | NULL                |
+----+----+---+---------------------+
1 row in set (0.0016 sec)

sql> 
Bye!
dvaneeden@dve-carbon:~$ mysqlsh mysql://root@127.0.0.1:4000/test

sql> SELECT *, TIDB_ROW_CHECKSUM() FROM t WHERE id = 1;
+----+----+---+---------------------+
| id | k  | c | TIDB_ROW_CHECKSUM() |
+----+----+---+---------------------+
|  1 | 10 | a | NULL                |
+----+----+---+---------------------+
1 row in set (0.0016 sec)

sql> delete from t;
Query OK, 1 row affected (0.0038 sec)

sql> INSERT INTO t values (1, 10, 'a');
Query OK, 1 row affected (0.0112 sec)

sql> SELECT *, TIDB_ROW_CHECKSUM() FROM t WHERE id = 1;
+----+----+---+---------------------+
| id | k  | c | TIDB_ROW_CHECKSUM() |
+----+----+---+---------------------+
|  1 | 10 | a | 3813955661          |
+----+----+---+---------------------+
1 row in set (0.0018 sec)

sql> 

[dveeden]

I'm not sure if the intended use of this function is clearly described. Is this only for TiCDC? Or is this also useful in other cases? How does this relate to ADMIN CHECKSUM TABLE?

[ti-chi-bot]

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[Oreoxmt]

Rest LGTM

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-05-31 06:01:31.484356613 +0000 UTC m=+3015445.241492178: ☑️ agreed by hfxsd.
• 2024-05-31 06:25:44.200848852 +0000 UTC m=+3016897.957984425: ☑️ agreed by Oreoxmt.

[hfxsd]

/approve

[ti-chi-bot]

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.1: #17699.