*: some tiny optimizations to reduce infoschema v2 memory

[tiancaiamao]

What problem does this PR solve?

Issue Number: ref #50959

Problem Summary:

What changed and how does it work?

1. Change some calling from SchemaTables() to SchemaTableInfos()

SchemaTables() is heavier than SchemaTableInfos() because the former need to load model.TableInfo from meta kv first and then build table.Table from model.TableInfo

The caller only need the model.TableInfo, so change them to SchemaTableInfos.

2. Reset Tables field of model.DBInfo when adding it to infoschema v2

I found some leaky memory occupation in infoschema v2:

It turn out to be that the model.DBInfo reference the Tables, so the memoy of json data can not be freed.

3. Skip refill cache In SchemaTables()

Fill cache in the list API cause the memory thrash and also CPU thrash.
Especally I find the cost of Sizeof() is much higher than estimated.
When we add to cache or evict cache, we need to call Sizeof() to calculate the size of an object.
Skip refill cache in SchemaTables() can avoid much of that.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

I create a lot of partition tables and watch the memory usage.
The first issue is co-exist of infoschema v1 and v2, cause the memory usage doubled.
We can workaround it by setting DefTiDBSchemaCacheSize > 0 rather than setting @@global.tidb_schema_cache_size. (not done in this pull request)

The second to third red square in the picture above shows the effect of this pull request.

• 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 @tiancaiamao. Thanks for your PR.

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[codecov]

Codecov Report

Attention: Patch coverage is 80.95238% with 8 lines in your changes are missing coverage. Please review.

Project coverage is 74.5301%. Comparing base (37b29bd) to head (93ac090).
Report is 7 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #53242        +/-   ##
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+ Coverage   72.4582%   74.5301%   +2.0719%     
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  Files          1493       1493                
  Lines        429362     429696       +334     
================================================
+ Hits         311108     320253      +9145     
+ Misses        98985      89537      -9448     
- Partials      19269      19906       +637     

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Components	Coverage Δ
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[tiancaiamao]

/retest-required

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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Needs approval from an approver in each of these files:

• OWNERS [hawkingrei,ywqzzy]
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• pkg/statistics/OWNERS [hawkingrei]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-05-14 06:32:14.314562188 +0000 UTC m=+1548488.071697763: ☑️ agreed by ywqzzy.
• 2024-05-14 08:24:45.319432574 +0000 UTC m=+1555239.076568151: ☑️ agreed by hawkingrei.

[hawkingrei]

/retest