VReplication: throttle on target tablet

[shlomi-noach]

Description

With this PR Vreplication throttles on writing to target tablet. This applied to both table-copy writes and binlog events writes.

The VReplication Engine throttles by using the standard check, which assumes the backend is a shard's primary tablet, and which throttles by shard's lag.

I'm not sure if there's a scenario where the target is a replica? If so, we can certainly also add check-self to the throttler's consideration.

Related Issue(s)

• Tracking issue: Tracking issue: VReplication throttling #7362
• Extends vstreamer to throttle on source endpoint #7324 (which in turn extends Tablet throttle: support "/throttle/check-self" available on all tablets #7319)

Checklist

• Should this PR be backported?
• Tests were added or are not required
• Documentation was added or is not required

Deployment Notes

Impacted Areas in Vitess

Components that this PR will affect:

• Query Serving
• VReplication
• Cluster Management
• Build
• VTAdmin

Because this PR extends #7324 it only makes sense to fully review it once #7324 is merged. Having said that, check out the specific changes under go/vt/vttablet/tabletmanager/vreplication/
cc @rohit-nayak-ps

[shlomi-noach]

This PR is ready; however, it does extend #7324 so it's best to first review that.

[rohit-nayak-ps]

What do you think of extracting the throttleStatusOK/throttle functions and related lagThrottler/lastSuccessfulThrottleCheck properties which are repeated in tableGC/vstreamer/vreplication into its own "class"?

[shlomi-noach]

What do you think of extracting the throttleStatusOK/throttle functions

Yes, let me look into it. One hidden but important difference in the two implementations is that source side calls CheckSelf and target side calls Check for throttling.

[rohit-nayak-ps]

lgtm

[shlomi-noach]

@rohit-nayak-ps I will refactor this PR a bit to consolidate the calls for throttle checks; will request an additional review afterwards.

[shlomi-noach]

@rohit-nayak-ps I've created a new throttler.Client which is used by:

• vstreamer Engine
• replicator Engine
• tablegc

and which offers the functionality of checking the throttler and backing off with sleep as necessary.