planner: add protection to avoid setting tot_col_size to negative numbers

[qw4990]

What problem does this PR solve?

Issue Number: close #55126

Problem Summary: planner: add protection to avoid setting tot_col_size to negative numbers

What changed and how does it work?

See more details and analysis in the issue.
When updating tot_col_size, use GREATEST to protect it from becoming a negative number.

Hard to use UT to test it, so I tested it manually locally:

First I hacked the code below to simulate all positive updates on tot_col_size are lost:

Then execute those SQLs:

mysql> create table t (a varchar(100), key(a));
Query OK, 0 rows affected (0.01 sec)

mysql> analyze table t;
Query OK, 0 rows affected, 2 warnings (0.03 sec)

mysql> insert into t values (space(100));
Query OK, 1 row affected (0.01 sec)

mysql> update t set a="";
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

Then we can see the tot_col_size becomes a negative number:

mysql> show stats_histograms;
+---------+------------+----------------+-------------+----------+---------------------+----------------+------------+--------------+-------------+-------------+-----------------+----------------+----------------+---------------+
| Db_name | Table_name | Partition_name | Column_name | Is_index | Update_time         | Distinct_count | Null_count | Avg_col_size | Correlation | Load_status | Total_mem_usage | Hist_mem_usage | Topn_mem_usage | Cms_mem_usage |
+---------+------------+----------------+-------------+----------+---------------------+----------------+------------+--------------+-------------+-------------+-----------------+----------------+----------------+---------------+
| test    | t          |                | a           |        0 | 2024-08-09 14:39:42 |              0 |          0 |         -101 |           0 | allLoaded   |               0 |              0 |              0 |             0 |
+---------+------------+----------------+-------------+----------+---------------------+----------------+------------+--------------+-------------+-------------+-----------------+----------------+----------------+---------------+

After this PR, this case won't happen, at least we can ensure it's equal or larger than 0:

mysql> show stats_histograms;
+---------+------------+----------------+-------------+----------+---------------------+----------------+------------+--------------+-------------+-------------+-----------------+----------------+----------------+---------------+
| Db_name | Table_name | Partition_name | Column_name | Is_index | Update_time         | Distinct_count | Null_count | Avg_col_size | Correlation | Load_status | Total_mem_usage | Hist_mem_usage | Topn_mem_usage | Cms_mem_usage |
+---------+------------+----------------+-------------+----------+---------------------+----------------+------------+--------------+-------------+-------------+-----------------+----------------+----------------+---------------+
| test    | t          |                | a           |        0 | 2024-08-09 14:47:16 |              0 |          0 |            0 |           0 | allLoaded   |               0 |              0 |              0 |             0 |
+---------+------------+----------------+-------------+----------+---------------------+----------------+------------+--------------+-------------+-------------+-----------------+----------------+----------------+---------------+

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[tiprow]

Hi @qw4990. Thanks for your PR.

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[hawkingrei]

/ok-to-test

[Rustin170506]

Looks good to me. Thanks! 👍

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hawkingrei, hi-rustin

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-08-09 06:51:19.449852286 +0000 UTC m=+594009.316951367: ☑️ agreed by hi-rustin.
• 2024-08-09 06:53:38.503660836 +0000 UTC m=+594148.370759922: ☑️ agreed by hawkingrei.

[qw4990]

/test mysql-test

[tiprow]

@qw4990: The specified target(s) for /test were not found.
The following commands are available to trigger required jobs:

• /test fast_test_tiprow
• /test tidb_parser_test

Use /test all to run all jobs.

In response to this:

/test mysql-test

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[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 75.3320%. Comparing base (b066365) to head (c57d6cd).
Report is 81 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #55327        +/-   ##
================================================
+ Coverage   74.7027%   75.3320%   +0.6292%     
================================================
  Files          1570       1570                
  Lines        364767     443291     +78524     
================================================
+ Hits         272491     333940     +61449     
- Misses        72509      88739     +16230     
- Partials      19767      20612       +845     

Flag	Coverage Δ
integration	51.1343% <75.0000%> (?)
unit	71.8280% <75.0000%> (-1.8035%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	52.9567% <ø> (-2.2327%)	⬇️
parser	∅ <ø> (∅)
br	62.9417% <ø> (+15.3240%)	⬆️

[hawkingrei]

/retest

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.5: #55380.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.1: #55523.

[winoros]

/cherrypick release-7.5
/cherrypick release-7.1

[ti-chi-bot]

@winoros: new pull request created to branch release-7.1: #55628.

In response to this:

/cherrypick release-7.5
/cherrypick release-7.1

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[ti-chi-bot]

@winoros: new pull request created to branch release-7.5: #55629.

In response to this:

/cherrypick release-7.5
/cherrypick release-7.1

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.