kv: expose isolation level through kv.Txn API

[nvanbenschoten]

Fixes #100130.

This commit exposes isolation levels through the kv.Txn API with the introduction of a new SetIsoLevel method. This method behaves similarly to SetUserPriority. Notably, the isolation must be set before any operations are performed on the transaction.

Release note: None

[cockroach-teamcity]

This change is 

[arulajmani]

Reviewed 5 of 5 files at r1, 16 of 16 files at r2, 6 of 6 files at r3, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @DrewKimball and @nvanbenschoten)

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pkg/kv/kvclient/kvcoord/txn_coord_sender_test.go line 74 at r3 (raw file):

// TestTxnCoordSenderAssignsTxnKey verifies that a transaction is assigned a
// transaction record key corresponding to the first key it writes.

Do you think it's worth extending this test to check for locking reads as well? Doesn't have to be in this patch.

[nvanbenschoten]

TFTR!

bors r=arulajmani

Reviewable status: complete! 0 of 0 LGTMs obtained (and 1 stale) (waiting on @arulajmani and @DrewKimball)

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pkg/kv/kvclient/kvcoord/txn_coord_sender_test.go line 74 at r3 (raw file):

Previously, arulajmani (Arul Ajmani) wrote…

Do you think it's worth extending this test to check for locking reads as well? Doesn't have to be in this patch.

TestTxnHeartbeaterLoopStartedOnFirstLock is a better test that sits alongside TestTxnHeartbeaterSetsTransactionKey and exercises that case, so I don't think we need anything more here. This test here is already of limited utility. I'm reviving it mostly because it gives coverage of a setting and getting a few txn attributes.

[craig]

Build failed:

• Bazel Essential CI (Cockroach)

[nvanbenschoten]

Bors flaked on a timeout in TestConcurrentMigrationAttempts, which is unrelated. I pinged #100873 (comment) and am going to give this another spin.

bors r+

[craig]

Build succeeded:

• Bazel Essential CI (Cockroach)