sql: disable stats injection within an explicit transaction

[rohany]

Fixes #42421.

Release justification: Disables a situation that could lead to a
deadlock.

Release note (sql change): Disables to ability to inject stats
within an explicit transaction.

[cockroach-teamcity]

This change is 

[RaduBerinde]

I don't think this works. There are two problems:

• the table stats cache is not scoped per txn; with this change, if the txn that injected stats gets aborted, the new stats will still stay in the cache and will be accessible. They are actually accessible to other queries even before the transaction commits or aborts.
• We want the stats cache to use a separate transaction which can be auto-retried on its own. We don't want a user transaction to get aborted because the table stats hit a conflict (because a table stat was recently refreshed).

I think we should just not support injecting statistics inside a transaction (or do the injection insert using a separate transaction so that it's not tied to the outer transaction).

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @RaduBerinde and @rytaft)

[rohany]

I see, I didn't consider those effects. That makes sense.

I think we should just not support injecting statistics inside a transaction (or do the injection insert using a separate transaction so that it's not tied to the outer transaction).

I'll play around with these ideas.

[rohany]

PTAL

Running the injection in a separate transaction leads to the same deadlock it seems. So I went ahead and disabled stats injection in explicit transactions.

[RaduBerinde]

Great, thanks for the fix!

Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @rohany and @rytaft)

---

pkg/sql/logictest/testdata/logic_test/alter_table, line 1120 at r1 (raw file):

statement error pq: cannot inject statistics in an explicit transaction
ALTER TABLE inject_stats INJECT STATISTICS '[
  {

[nit] this can probably just be []. We definitely don't need these crazy counts :)

[rohany]

lol true :D

bors r+

[craig]

Build failed (retrying...)

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[craig]

Build succeeded

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