planner: add protection to avoid setting tot_col_size to negative numbers (#55327)

[ti-chi-bot]

This is an automated cherry-pick of #55327

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

[fixdb]

+1

[codecov]

Codecov Report

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

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Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.1     #55523   +/-   ##
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  Files                  ?       1466           
  Lines                  ?     423367           
  Branches               ?          0           
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  Misses                 ?     101138           
  Partials               ?      20470           

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Components	Coverage Δ
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parser	∅ <0.0000%> (?)
br	41.3284% <0.0000%> (?)

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: fixdb, hawkingrei

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-08-20 06:45:09.347973819 +0000 UTC m=+247904.482423936: ☑️ agreed by fixdb.
• 2024-08-20 09:40:37.06236669 +0000 UTC m=+258432.196816816: ☑️ agreed by hawkingrei.