[BugFix] Fix bad case of pindex

[sevev]

Why I'm doing:
The default max memory usage of one pindex is 100MB right now, so if the pindex memory usage is less than 100MB, it does not flush a l1 file to disk. To avoid keeping too many WAL logs in l0 file, we will compare the l0 file size and the memory usage. However, due to memory alignment, the size of L0 files is not always larger than the memory usage. This causes Pindex to dump a new snapshot each time, resulting in significant disk I/O when the snapshot file is large.

What I'm doing:
Dump a new snapshot only the L0 file size is too large.

Fixes #issue

What type of PR is this:

• BugFix
• Feature
• Enhancement
• Refactor
• UT
• Doc
• Tool

Does this PR entail a change in behavior?

• Yes, this PR will result in a change in behavior.
• No, this PR will not result in a change in behavior.

If yes, please specify the type of change:

• Interface/UI changes: syntax, type conversion, expression evaluation, display information
• Parameter changes: default values, similar parameters but with different default values
• Policy changes: use new policy to replace old one, functionality automatically enabled
• Feature removed
• Miscellaneous: upgrade & downgrade compatibility, etc.

Checklist:

• I have added test cases for my bug fix or my new feature
• This pr needs user documentation (for new or modified features or behaviors)
  • I have added documentation for my new feature or new function
• This is a backport pr

Bugfix cherry-pick branch check:

• I have checked the version labels which the pr will be auto-backported to the target branch
  • 3.2
  • 3.1
  • 3.0
  • 2.5

[github-actions]

[FE Incremental Coverage Report]

✅ pass : 0 / 0 (0%)

[github-actions]

[BE Incremental Coverage Report]

✅ pass : 1 / 1 (100.00%)

file detail

	path	covered_line	new_line	coverage	not_covered_line_detail
🔵	be/src/storage/persistent_index.cpp	1	1	100.00%	[]

[github-actions]

@Mergifyio backport branch-3.2

[github-actions]

@Mergifyio backport branch-3.1

[github-actions]

@Mergifyio backport branch-3.0

[mergify]

backport branch-3.2

✅ Backports have been created

• #40044 [BugFix] Fix bad case of pindex (backport #39959) has been created for branch branch-3.2

[mergify]

backport branch-3.1

✅ Backports have been created

• #40045 [BugFix] Fix bad case of pindex (backport #39959) has been created for branch branch-3.1

[github-actions]

@Mergifyio backport branch-2.5

[mergify]

backport branch-3.0

✅ Backports have been created

• #40046 [BugFix] Fix bad case of pindex (backport #39959) has been created for branch branch-3.0

[mergify]

backport branch-2.5

✅ Backports have been created

• #40047 [BugFix] Fix bad case of pindex (backport #39959) has been created for branch branch-2.5