VReplication: Use MariaDB Compat JSON Functions

[mattlord]

Description

This is needed to better support importing from MariaDB to Vitess/MySQL as we leverage MySQL's JSON support more and more in VReplication.

While we do not fully support MariaDB in Vitess v16 and later (where VDiff2 is GA and the default), we DO want to support easy and reliable imports from MariaDB to Vitess and MySQL. This is also a pretty easy and straightforward fix — as col1->>'$.field1' is equivalent to JSON_UNQUOTE(JSON_EXTRACT(col1, '$.field1')) — and doing so allows us to fully support VDiff2 with MariaDB imports, even when running the VDiffs against the reverse workflows after SwitchTraffic is done (which are then executed on the source MariaDB instance).

Note VDiffs are not typically run against the _reverse workflows. Without attempting those, you would get a couple of vttablet log messages per minute on the source primary tablet(s) that the attempt to find VDiffs to retry failed due to the unsupported syntax used. And even if you did attempt one, this would only prevent a VDiff that had encountered an initial error for any reason from being retried (it would be permanently failed). So this is a relatively minor fix, but one certainly worth doing.

Related Issue(s)

• Fixes: Bug Report: MariaDB support broken in vdiff2 #12419

Checklist

• "Backport to:" labels have been added if this change should be back-ported
• Tests were added or are not required
• Documentation was added or is not required

[mattlord]

The OnlineDDL VReplication test failures are a known unrelated issue that is being worked on.

[dbussink]

The OnlineDDL VReplication test failures are a known unrelated issue that is being worked on.

@mattlord Is this something we could relatively easily test in the MariaDB migration job that we have? That it also tests a vdiff both ways?

[GuptaManan100]

LGTM

[mattlord]

The OnlineDDL VReplication test failures are a known unrelated issue that is being worked on.

@mattlord Is this something we could relatively easily test in the MariaDB migration job that we have? That it also tests a vdiff both ways?

I double checked... we do already do this today:

vitess/go/test/endtoend/vreplication/vreplication_test.go

Line 773 in a5d0cdc

vdiff1(t, "product.p2c_reverse", "")

What wouldn't have worked on the reverse workflow is the auto retry on error (because the query used to find VDiffs that should be retried failed due to the invalid syntax). But you could still manually [re]start the workflow:

• Stop (clear the error and mark it as stopped): https://vitess.io/docs/16.0/reference/vreplication/vdiff/#stopping-a-vdiff
• Resume: https://vitess.io/docs/16.0/reference/vreplication/vdiff/#resume-a-previous-vdiff

Or of course you could run another VDiff, which is what you always had to do with VDiff1 if you encountered an error.

So again, I think in practice this is a pretty minor issue but again, one that I think is still definitely worth doing.

If we do at some point decide that it's worth adding a VDiff2 auto retry test specifically with MariaDB, then we could effectively duplicate this test: https://github.com/vitessio/vitess/blob/main/go/test/endtoend/vreplication/vdiff2_test.go#L102

And use MariaDB for the keyspaces.

[rohit-nayak-ps]

lgtm