ddl notifier: use pagination for SELECT to reduce memory usage #58376

lance6716 · 2024-12-18T08:16:05Z

What problem does this PR solve?

Issue Number: close #58368

Problem Summary:

What changed and how does it work?

as title. refine the Store.List.

// Store is the (de)serialization and persistent layer.
type Store interface {
...
	// List will start a transaction of given session and read all schema changes
	// through a ListResult. The ownership of session is occupied Store until CloseFn
	// is called.
	List(ctx context.Context, se *sess.Session) ListResult
}

// ListResult is the result stream of a List operation.
type ListResult interface {
	// Read tries to decode at most `len(changes)` SchemaChange into given slices. It
	// returns the number of schemaChanges decoded, 0 means no more schemaChanges.
	//
	// Note that the previous SchemaChange in the slice will be overwritten when call
	// Read.
	Read(changes []*SchemaChange) (int, error)
}

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

Release note

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

None

Signed-off-by: lance6716 <[email protected]>

tiprow · 2024-12-18T08:16:22Z

Hi @lance6716. Thanks for your PR.

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lance6716 · 2024-12-18T08:20:48Z

/check-issue-triage-complete

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (1)

pkg/ddl/notifier/subscribe.go:171

The variable name ProcessEventsBatchSize is clear and consistent with the changes made throughout the code.

var ProcessEventsBatchSize = 1024

Signed-off-by: lance6716 <[email protected]>

codecov · 2024-12-18T08:44:27Z

Codecov Report

Attention: Patch coverage is 82.45614% with 20 lines in your changes missing coverage. Please review.

Project coverage is 75.2997%. Comparing base (1405c5e) to head (9536b86).
Report is 44 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #58376        +/-   ##
================================================
+ Coverage   73.1849%   75.2997%   +2.1148%     
================================================
  Files          1681       1727        +46     
  Lines        463027     480149     +17122     
================================================
+ Hits         338866     361551     +22685     
+ Misses       103358      96359      -6999     
- Partials      20803      22239      +1436

Flag	Coverage Δ
integration	`49.3698% <76.3157%> (?)`
unit	`72.7383% <82.4561%> (+0.4215%)`	⬆️

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

Components	Coverage Δ
dumpling	`53.0100% <ø> (+0.3190%)`	⬆️
parser	`∅ <ø> (∅)`
br	`60.8815% <ø> (+14.8795%)`	⬆️

lance6716 · 2024-12-18T09:09:47Z

/retest

tiprow · 2024-12-18T09:10:09Z

@lance6716: Cannot trigger testing until a trusted user reviews the PR and leaves an /ok-to-test message.

In response to this:

/retest

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pkg/ddl/notifier/store.go

tiancaiamao · 2024-12-19T10:23:43Z

pkg/ddl/notifier/subscribe.go

+	changes := make([]*SchemaChange, ProcessEventsBatchSize)
+
+	for {
+		count, err2 := result.Read(changes)


Why not let read return []*SchemaChange directly?
Return count and use changes[:count] is just a unnecessary detour

It's like an io.Reader calling convention which is caller pass-in slices so caller can reuse the previous results. Because we are in 1M tables project, I'm afraid that returning 1M []*SchemaChange (it also has internal pointers like TableInfo) will add pressure to GC.

Though it's less common, I think this package / function is the only caller of ListResult.Read. Other developers will not modify this package and will not be confused by it.

However I notice that I use json.Unmarshal on an non-empty object, not sure the leftover of the object will be overwritten or causes some problems. I'll check it tomorrow.

What was your test result?

pass-in slices so caller can reuse the previous results

Yes, I mean the same thing, just that the code can be write as:

func f(changes []*SchemaChange) []*SchemaChange { ret := changes[:0] ret = append(ret, xxx) return ret }

Anyway, this is just some personal taste, so you can choose to accept it or not.

What was your test result?

I didn't test it yet 😂 I hope other colleague can help check it. Theoretically there's no big query now.

func f(changes []*SchemaChange) []*SchemaChange {

In this new signature, the batch size of one Read is not obvious when input is nil, or it seems like an append where the slice will be grown and batch size is not be limited. Your suggestion is like EncodeBytes but here we want to control the batch size as well as reuse buffer.

Signed-off-by: lance6716 <[email protected]>

Rustin170506

Better to verify if this can fix the memory consumption issue. before merging it.

Thanks!

/hold

Rustin170506 · 2024-12-23T04:09:23Z

pkg/ddl/notifier/store.go

+		if changes[i] == nil {
+			changes[i] = new(SchemaChange)
+		}
+		if changes[i].event == nil {
+			changes[i].event = new(SchemaChangeEvent)
+		}
+		if changes[i].event.inner == nil {
+			changes[i].event.inner = new(jsonSchemaChangeEvent)
+		}


How about:

// Add constructor function func NewSchemaChange() *SchemaChange { return &SchemaChange{ event: &SchemaChangeEvent{ inner: &jsonSchemaChangeEvent{}, }, } } if changes[i] == nil { changes[i] = NewSchemaChange() }

Or do you mean there is a case that changes[i] is not nil, but the event or the inner is nil?

just to improve robustness, I don't want to assume caller uses some kind of SchemaChange.

I'll test the OOM problem soon

ti-chi-bot · 2024-12-23T04:11:20Z

[LGTM Timeline notifier]

Timeline:

2024-12-20 10:14:14.361822185 +0000 UTC m=+1211044.450624723: ☑️ agreed by tiancaiamao.
2024-12-23 04:11:19.650829735 +0000 UTC m=+1448469.739632278: ☑️ agreed by Rustin170506.

tiprow · 2024-12-23T04:14:20Z

@lance6716: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
fast_test_tiprow	`9536b86`	link	true	`/test fast_test_tiprow`

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D3Hunter · 2024-12-23T11:12:33Z

/approve

ti-chi-bot · 2024-12-23T11:12:41Z

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: D3Hunter, Rustin170506, tiancaiamao

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lance6716 · 2024-12-23T13:00:32Z

/unhold

due to test resource limit, I can't create a test cluster before the coming version release. So I plan to test the effect later, and don't cherry-pick to v8.5.1 before we get the test result

lance6716 · 2024-12-23T13:00:39Z

/retest

tiprow · 2024-12-23T13:01:00Z

@lance6716: Cannot trigger testing until a trusted user reviews the PR and leaves an /ok-to-test message.

In response to this:

/retest

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ti-chi-bot · 2024-12-23T14:31:25Z

In response to a cherrypick label: new pull request created to branch release-8.5: #58488.

ddl notifier: use pagination for SELECT to reduce memory usage

d0d2dde

Signed-off-by: lance6716 <[email protected]>

ti-chi-bot bot added release-note-none Denotes a PR that doesn't merit a release note. do-not-merge/needs-triage-completed size/XL Denotes a PR that changes 500-999 lines, ignoring generated files. labels Dec 18, 2024

lance6716 requested a review from Copilot December 18, 2024 08:16

Rustin170506 requested review from Rustin170506 and time-and-fate and removed request for Copilot December 18, 2024 08:17

lance6716 requested a review from Copilot December 18, 2024 08:20

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lance6716 requested a review from wjhuang2016 December 18, 2024 08:23

fix bazel

7bdf750

Signed-off-by: lance6716 <[email protected]>

tiancaiamao reviewed Dec 19, 2024

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pkg/ddl/notifier/store.go Show resolved Hide resolved

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lance6716 added 3 commits December 20, 2024 17:35

address comment

378a648

Signed-off-by: lance6716 <[email protected]>

fix bazel

9b253d5

Signed-off-by: lance6716 <[email protected]>

change comment

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Signed-off-by: lance6716 <[email protected]>

tiancaiamao approved these changes Dec 20, 2024

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ti-chi-bot bot added the needs-1-more-lgtm Indicates a PR needs 1 more LGTM. label Dec 20, 2024

add license

9536b86

Signed-off-by: lance6716 <[email protected]>

Rustin170506 approved these changes Dec 23, 2024

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ti-chi-bot bot added do-not-merge/hold Indicates that a PR should not merge because someone has issued a /hold command. lgtm and removed needs-1-more-lgtm Indicates a PR needs 1 more LGTM. labels Dec 23, 2024

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ti-chi-bot bot merged commit 5fbe4fb into pingcap:master Dec 23, 2024
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ddl notifier: use pagination for SELECT to reduce memory usage (#58376) #58488

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ddl notifier: use pagination for SELECT to reduce memory usage #58376

ddl notifier: use pagination for SELECT to reduce memory usage #58376

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ddl notifier: use pagination for SELECT to reduce memory usage #58376

ddl notifier: use pagination for SELECT to reduce memory usage #58376

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lance6716 commented Dec 18, 2024 • edited Loading

What problem does this PR solve?

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[LGTM Timeline notifier]

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