Storages: Splitting DMFileReaderPool to reduce lock contention

[JinheLin]

What problem does this PR solve?

Issue Number: close #9125

Problem Summary:

What is changed and how it works?

Reduce the lock contention on DMFileReaderPool::mtx by splitting the dmfiles by hash(file_path) of 16

Check List

Tests

• [ ] Unit test
• [ ] Integration test
• [x] Manual test (add detailed scripts or steps below)
  • Run simple queries (select max(k) from sbtest1) concurrently.
  • Time consumption unit: ms.

Concurrency	Master	This PR
1	27	25
2	28	29
4	46	46
8	72	77
16	124	97
32	232	160
64	450	327

• [ ] No code

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

Improve the short queries performance under high concurrency by reducing the lock contention

[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: JaySon-Huang, Lloyd-Pottiger

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/pingcap/tiflash/blob/master/OWNERS)~~ [JaySon-Huang,Lloyd-Pottiger] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[ti-chi-bot[bot]]

[LGTM Timeline notifier]

Timeline:

• 2024-06-06 08:55:20.530060557 +0000 UTC m=+22874.583372481: :ballot_box_with_check: agreed by JaySon-Huang.
• 2024-06-07 03:07:01.693031429 +0000 UTC m=+88375.746343350: :ballot_box_with_check: agreed by Lloyd-Pottiger.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.1: #9129.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #9130.