Online DDL: fast (and correct) RANGE PARTITION operations, 1st iteration #10315

shlomi-noach · 2022-05-16T08:20:49Z

Description

This PR introduces support for fast ADD PARTITION and DROP PARTITION in RANGE partitioned tables. At this time these fast migrations are not revertible, but a future iteration will make them revertible.

Why, what's the problem with existing implementation?

For both speed and correctness.

Speed: adding a new range partition is a simple operation, which does not require a full blown online schema change that copies the entire table over. The MySQL implementation for adding a partition is creating an empty table.
Correctness: in a range partitioned table, dropping the oldest partition should also delete all data in that partition. However, the way all online-schema-change tools are built, including vitess's vitess migrations, handles this incorrectly. When you DROP PARTITION in an online schema change tool, the tool creates a shadow table with that partition removed. It then copies over all table rows from the original table. What used to be the 2nd partition (now the first after dropping the oldest partition) turns out to be a good host for all the old partition's rows. The end result is that no rows are deleted in the process. Which not what the user wanted.

How

Confronted with an ALTER TABLE statement, and before sending it over to the appropriate handler (vitess, gh-ost, pt-osc), the executor checks if it can execute the migration using a "special plan". By parsing and analyzing the exact semantics of the query, vitess is able to know a statement is a ADD|DROP of a RANGE PARTITION; and if that is the case, it executes the query directly on the backend MySQL server, rather then invoke an OSC.

Limitations

At this time, these migrations are not revertible. There is a path and plan to make them revertible in a next iteration.
In anticipation of making these operations revertible, a ALTER TABLE ... DROP PARTITION may only drop one partition at a time (the MySQL syntax allows dropping multiple partitions at once).
Right now and while this is a new and in progress behavior, it is protected by a new and undocumented ~~--fast-over-revertible~~ --fast-range-rotation flag in ddl_strategy. This flag will be useful to additional migration types, but we expect it to eventually be irrelevant to ADD|DROP PARTITION queries, as we do intend to make them revertible.

There are no release notes in the meantime as I want to see how next iterations make progress. No documentation for this new behavior yet until we consider it stable.

Related Issue(s)

Checklist

"Backport me!" label has been added if this change should be backported
Tests were added or are not required
Documentation was added or is not required

Deployment Notes

Signed-off-by: Shlomi Noach <[email protected]>

…olumn including full partition spec Signed-off-by: Shlomi Noach <[email protected]>

Signed-off-by: Shlomi Noach <[email protected]>

github-actions · 2022-05-16T08:21:15Z

dbussink · 2022-05-16T08:34:52Z

go/vt/schema/ddl_strategy.go

@@ -150,6 +151,11 @@ func (setting *DDLStrategySetting) IsAllowConcurrent() bool {
 	return setting.hasFlag(allowConcurrentFlag)
 }

+// IsFastOverRevertibleFlag checks if strategy options include -fast-ver-revertible


fast-ver-revertible -> fast-over-revertible

dbussink · 2022-05-16T08:36:21Z

go/vt/vttablet/onlineddl/analysis.go

+}
+
+// analyzeDropFirstOrLastRangePartition sees if the online DDL drops the first or last partition
+//  in a range partitioned table


Isn't this only checking if it's the first partition?

And isn't adding checking if it's adding the last? So is this comment here correct?

fixed. The code was refactored into a more general form, and the original comment was left behind.

dbussink · 2022-05-16T08:36:41Z

go/vt/vttablet/onlineddl/analysis.go

+}
+
+// analyzeDropFirstOrLastRangePartition sees if the online DDL drops the first or last partition
+//  in a range partitioned table


Same here, I think the comment is wrong.

dbussink · 2022-05-16T08:36:55Z

go/vt/vttablet/onlineddl/analysis.go

+	partitionName := partitionDefinition.Name.String()
+	// OK then!
+
+	// Now, is this query adding a parititon in a RANGE partitioned table?


parititon -> partition

dbussink · 2022-05-16T08:37:16Z

go/vt/vttablet/onlineddl/analysis.go

+
+// analyzeSpecialAlterScenarios checks if the given ALTER onlineDDL, and for the current state of affected table,
+// can be executed in a special way
+func (e *Executor) analyzeSpecialAlterPlan(ctx context.Context, onlineDDL *schema.OnlineDDL) (*SpecialAlterPlan, error) {


Comment is wrong for the function name here.

Signed-off-by: Shlomi Noach <[email protected]>

shlomi-noach · 2022-05-16T10:40:43Z

Ugh edited online and that lost the signature. Gonna force-push shortly.

Signed-off-by: Shlomi Noach <[email protected]>

shlomi-noach · 2022-05-16T12:37:32Z

Related, design proposal: #10317

This PR implements the forward migration aspect.

dbussink · 2022-05-16T12:59:47Z

Right now and while this is a new and in progress behavior, it is protected by a new and undocumented --fast-over-revertible flag in ddl_strategy. This flag will be useful to additional migration types, but we expect it to eventually be irrelevant to ADD|DROP PARTITION queries, as we do intend to make them revertible.

This was a thing I had most questions over reading the code, but I think this makes sense. My concern was mostly on whether it's needed to control revertible or not strategies at a finer level or not, say, wanting to use it for partitions but not for an INSTANT ADD COLUMN style DDL operation.

But if this flag becomes eventually irrelevant for partitions, I think most of that concern disappears. That's also because partitions seem to be quite a different beast in general but with a separate strategy for dealing with them as discussed in #10317 I think we're ok.

So tl;dr, I think that if we would keep partitions as is without #10317, we would want to have a separate flag to control partitions vs. other fast over revertible cases, but given #10317 I don't think we need that (so one flag is better then I think).

shlomi-noach · 2022-05-16T13:05:25Z

if we would keep partitions as is without #10317, we would want to have a separate flag to control partitions vs. other fast over revertible cases,

My thought as well, these probably deserve different flags. Let's see how we make progress.

dbussink · 2022-05-16T13:00:59Z

go/vt/vttablet/onlineddl/analysis.go

+	partitionName := spec.Names[0].String()
+	// OK then!
+
+	// Now, is this query dropping the first parititon in a RANGE partitioned table?


parititon -> partition.

Signed-off-by: Shlomi Noach <[email protected]>

shlomi-noach · 2022-05-16T14:12:13Z

Out of caution, added a new ddl_strategy flag, --fast-range-rotation, which is now what the new fast ADD/DROP PARTITION functionality requires.

--fast-over-revertible remains for now, unused. I see a future for --fast-over-revertible for other types of migrations.

Both flags remain undocumented.

Signed-off-by: Shlomi Noach <[email protected]>

shlomi-noach · 2022-05-23T14:40:41Z

Ping for review from the Vitess team

deepthi

LGTM

shlomi-noach added 8 commits May 11, 2022 17:29

analysis of a special ALTER plan

c36e4df

Signed-off-by: Shlomi Noach <[email protected]>

operate a ADD PARTITION statement

733c52f

Signed-off-by: Shlomi Noach <[email protected]>

Merge branch 'main' into online-ddl-range-partition-fast

ecf25fa

Signed-off-by: Shlomi Noach <[email protected]>

fast DROP PARTITION flow

6504396

Signed-off-by: Shlomi Noach <[email protected]>

ddl strategy: --fast-over-revertible flag

d52abe5

Signed-off-by: Shlomi Noach <[email protected]>

Merge branch 'main' into online-ddl-range-partition-fast

7326c1a

Signed-off-by: Shlomi Noach <[email protected]>

support dropping any partition; more detail written to special plan c…

2ac26de

…olumn including full partition spec Signed-off-by: Shlomi Noach <[email protected]>

endtoend tests: at this time partition operations are not revertible

88e8577

Signed-off-by: Shlomi Noach <[email protected]>

shlomi-noach added Type: Bug Type: Enhancement Logical improvement (somewhere between a bug and feature) Component: Query Serving release notes none labels May 16, 2022

shlomi-noach requested review from rohit-nayak-ps, a team and dbussink May 16, 2022 08:20

dbussink reviewed May 16, 2022

View reviewed changes

fixes per review

42efec5

Signed-off-by: Shlomi Noach <[email protected]>

fix auto_increment query

e535497

Signed-off-by: Shlomi Noach <[email protected]>

shlomi-noach force-pushed the online-ddl-range-partition-fast branch from d6de80c to e535497 Compare May 16, 2022 10:41

shlomi-noach mentioned this pull request May 16, 2022

Design: REVERT for fast ADD|DROP PARTITION for range partitioned tables #10317

Closed

dbussink reviewed May 16, 2022

View reviewed changes

shlomi-noach added 3 commits May 16, 2022 17:08

added --fast-range-rotation ddl strategy flag

0a45b1a

Signed-off-by: Shlomi Noach <[email protected]>

typo

2007c40

Signed-off-by: Shlomi Noach <[email protected]>

using --fast-range-rotation for partition DDLs

5b09672

Signed-off-by: Shlomi Noach <[email protected]>

resolve conflict

8e6fbe3

Signed-off-by: Shlomi Noach <[email protected]>

shlomi-noach mentioned this pull request May 19, 2022

ON HOLD: Revertible fast partition migrations #10337

Closed

6 tasks

shlomi-noach added 3 commits May 22, 2022 09:27

merge main, resolve conflict

3bcb690

Signed-off-by: Shlomi Noach <[email protected]>

Merge branch 'main' into online-ddl-range-partition-fast

93a0f99

Signed-off-by: Shlomi Noach <[email protected]>

remove excessivle comments

4e981be

Signed-off-by: Shlomi Noach <[email protected]>

shlomi-noach added release notes and removed release notes none labels May 24, 2022

deepthi self-requested a review May 26, 2022 13:20

deepthi approved these changes May 28, 2022

View reviewed changes

deepthi merged commit 0b0fcae into vitessio:main May 28, 2022

deepthi deleted the online-ddl-range-partition-fast branch May 28, 2022 21:42

This was referenced May 29, 2022

Replace 'CREATE TABLE LIKE' with programmatic copy #10381

Merged

Online DDL: support INSTANT DDL special plan, flag protected (flag undocumented for now) #10402

Merged

shlomi-noach mentioned this pull request Oct 26, 2022

DDL strategy flags: document --fast-range-rotation vitessio/website#1197

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shlomi-noach mentioned this pull request Apr 8, 2024

Tracking: Online DDL partitioning changes improved support #15674

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Online DDL: fast (and correct) RANGE PARTITION operations, 1st iteration #10315

Online DDL: fast (and correct) RANGE PARTITION operations, 1st iteration #10315

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Online DDL: fast (and correct) RANGE PARTITION operations, 1st iteration #10315

Online DDL: fast (and correct) RANGE PARTITION operations, 1st iteration #10315

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shlomi-noach commented May 16, 2022 • edited Loading

Description

Why, what's the problem with existing implementation?

How

Limitations

Related Issue(s)

Checklist

Deployment Notes

github-actions bot commented May 16, 2022

Review Checklist

General

Bug fixes

Non-trivial changes

New/Existing features

Backward compatibility

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