release-24.1: sql: fix crash when planning stats collection on virtual col with UDT

[michae2]

Backport 1/1 commits from #123926.

/cc @cockroachdb/release

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CREATE STATISTICS executes in multiple layers: the "outer" layer is a normal execution of the CREATE STATISTICS statement. During this execution, we create, start, and await a CreateStats job. The CreateStats job in turn starts an "inner" layer which uses a separate internal transaction to plan and execute distributed statistics collection.

Within the inner layer, we were using the job's planner (JobExecContext) to plan distributed stats collection. This planner has no associated transaction. If it weren't for user-defined types, this would be fine, but user-defined types must be resolved using a transaction.

We had a hack in place to set the evalCtx.Txn to the internal transaction in order to execute collection on normal columns with user-defined type. But this hack did not work for virtual computed columns with user-defined type, because type-checking their expressions uses more facilites of the planner than just the evalCtx. (Specifically the schemaResolver.)

So, instead of setting the evalCtx.Txn, we create a new "inner" planner that is associated with the internal transaction of the inner layer. This works for all columns with user-defined type.

Fixes: #123821

Release note (bug fix): Fix a crash introduced in v24.1.0-beta.2 that could occur when planning statistics collection on a table with a virtual computed column using a user-defined type when the newly-introduced cluster setting sql.stats.virtual_computed_columns.enabled is set to true. (The setting was introduced in v24.1.0-alpha.1 default true.)

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Release justification: fix for GA-blocker node crash.

[blathers-crl]

Thanks for opening a backport.

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[cockroach-teamcity]

This change is 

[yuzefovich]

Reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @mgartner and @michae2)

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pkg/sql/create_stats.go line 662 at r1 (raw file):

	r.tableID = details.Table.ID
	evalCtx := jobsPlanner.ExtendedEvalContext()

nit: it might be a bit cleaner to move this line below the Txn anonymous function.

[michae2]

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @mgartner and @yuzefovich)

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pkg/sql/create_stats.go line 662 at r1 (raw file):

Previously, yuzefovich (Yahor Yuzefovich) wrote…

nit: it might be a bit cleaner to move this line below the Txn anonymous function.

Good point, and this would have caught a bug introduced by backport skew... one minute.

[mgartner]

Reviewed 1 of 2 files at r1, 1 of 1 files at r2, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @yuzefovich)

[michae2]

TFTRs! Trying to kick CI with a rebase...