vreplication timeout query optimizer hints

[olyazavr]

Description

When we try to run online ddl operations using the Vitess strategy, we see certain migrations on specific keyspace/tables fail due to timeout. The suggestion in slack was to increase mysql's max_execution_time, which did the trick, but we would like to limit this to only vreplication, not affecting any other query.

To do so, I have used the vreplication_copy_phase_duration flag and added /*+ MAX_EXECUTION_TIME(x) */ where x is the value of vreplication_copy_phase_duration to the vreplication queries. This involved moving the vreplication_copy_phase_duration duration flag to avoid circular dependencies

I tested this in our own environment with the previously failing schema migration and saw it make progress and complete with a 1hr setting for this flag.

Update: This has now been running in production and we no longer see online ddl schema migrations fail because of query timeouts. We see large/busy keyspaceshards able to run migrations where they previously were unable with ghost or vitess

Related Issue(s)

Fixes #14081

Checklist

• "Backport to:" labels have been added if this change should be back-ported
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on the CI
• Documentation was added or is not required

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[vitess-bot]

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[olyazavr]

I got feedback to not move the flag to another package, but I get circular dependencies otherwise, not sure how to proceed here

[rohit-nayak-ps]

I got feedback to not move the flag to another package, but I get circular dependencies otherwise, not sure how to proceed here

Sorry, meant to take a look at this earlier. My thought was to move the flag to tablet-level. I will take a look first thing tomorrow and push to this PR if that is OK.

I can take a look at the failing unit tests too then.

[rohit-nayak-ps]

Sorry, meant to take a look at this earlier. My thought was to move the flag to tablet-level. I will take a look first thing tomorrow and push to this PR if that is OK.

This commit moves the flag to the vttablet level.

I can take a look at the failing unit tests too then.

Didn't look at the failing tests since I saw you had some recent commits to try to address them. Let me know if you want me to take a look at them.

[olyazavr]

Thanks for that commit, I've pulled it in! I took a stab at the tests, but I would love some help with the remaining ones

[rohit-nayak-ps]

Thanks for that commit, I've pulled it in! I took a stab at the tests, but I would love some help with the remaining ones

Only one other test related to noblob seems to be failing. Here is the commit that fixes it: 99e1dfd. For noblob there is another set of queries that need the timeout hint, which I have added in that commit.

Can you pull that and let's see if all tests pass? Thanks.

[olyazavr]

Tests are all now passing! I'm also trying to find someone with permissions to update the hubspot repo settings so others can actually push to my branches 😅

[rohit-nayak-ps]

@olyazavr, great, good to see that all tests are passing.

Following up on the slack thread regarding this issue: did this PR fix your existing issue? Especially the fact that we are adding the timeout hints on the target for the insert/updates. Usually we have been seeing issues on the source while selecting rows in the copy phase. So just wanted to confirm that it does work.

Can you also add your specific findings to the description in the issue, just so that we have it all in one place? Thanks!

[olyazavr]

Yes, it did fix the issue, and we are now able to run migrations on larger/busier keyspaceshards that previously could not run schema migrations on ghost or vitess (:

If the question is do we need the timeout hints for anything other than the selects - I confess I didn't try this out, and added the timeout hints in all places to be consistent, and because it seemed like there was no downside to having all vreplication queries be allowed to run longer

I did not test this with any other usage of vreplication other than online ddl schema migrations

[rohit-nayak-ps]

@olyazavr we don't need this as well. We are essentially selecting static values which are used in inserts. So the tabletmanager\vreplication package doesn't need the optimizer hints anywhere.

[rohit-nayak-ps]

lgtm

Thanks for this @olyazavr, this should be very useful to resolve issues that we have seen occassionally with users with large clusters.

[olyazavr]

Rebased and dealt with merge conflicts

[olyazavr]

Looks like all checks are passing, anything else for me to do here?

[mattlord]

I will open a PR to update the docs here: https://vitess.io/docs/19.0/reference/vreplication/flags/#vreplication_copy_phase_duration

After this PR the flag is applicable on BOTH the source and target keyspaces:

1. On the target as it is used for the context used in the RPC to the source tablet by the vcopier:

   vitess/go/vt/vttablet/tabletmanager/vreplication/vcopier.go

   Lines 395 to 423 in 59408f9

   	ctx, cancel := context.WithTimeout(ctx, vttablet.CopyPhaseDuration)
   	defer cancel()
   	var lastpkpb *querypb.QueryResult
   	if lastpkqr := copyState[tableName]; lastpkqr != nil {
   	lastpkpb = sqltypes.ResultToProto3(lastpkqr)
   	}
   	rowsCopiedTicker := time.NewTicker(rowsCopiedUpdateInterval)
   	defer rowsCopiedTicker.Stop()
   	copyStateGCTicker := time.NewTicker(copyStateGCInterval)
   	defer copyStateGCTicker.Stop()
   	parallelism := getInsertParallelism()
   	copyWorkerFactory := vc.newCopyWorkerFactory(parallelism)
   	copyWorkQueue := vc.newCopyWorkQueue(parallelism, copyWorkerFactory)
   	defer copyWorkQueue.close()
   	// Allocate a result channel to collect results from tasks.
   	resultCh := make(chan *vcopierCopyTaskResult, parallelism*4)
   	defer close(resultCh)
   	var lastpk *querypb.Row
   	var pkfields []*querypb.Field
   	// Use this for task sequencing.
   	var prevCh <-chan *vcopierCopyTaskResult
   	serr := vc.vr.sourceVStreamer.VStreamRows(ctx, initialPlan.SendRule.Filter, lastpkpb, func(rows *binlogdatapb.VStreamRowsResponse) error {

2. On the source as it is used when building the query by the row streamer that runs there:

   vitess/go/vt/vttablet/tabletserver/vstreamer/rowstreamer.go

   Lines 458 to 460 in 59408f9

   	func GetVReplicationMaxExecutionTimeQueryHint() string {
   	return fmt.Sprintf("/*+ MAX_EXECUTION_TIME(%v) */ ", vttablet.CopyPhaseDuration.Milliseconds())
   	}

[mattlord]

vitessio/website#1797