opt: add enable_durable_locking_for_serializable session variable #107749
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DrewKimball
approved these changes
Jul 27, 2023
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Reviewed 8 of 8 files at r1, all commit messages.
Reviewable status:complete! 1 of 0 LGTMs obtained (waiting on @nvanbenschoten)
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You'll have to regenerate the |
Follow-up from cockroachdb#105857 This commit ammends 6a3e43d to add a session variable to control whether guaranteed-durable locks are used under serializable isolation. Informs: cockroachdb#100194 Epic: CRDB-25322 Release note (sql change): Add a new session variable, `enable_durable_locking_for_serializable`, which controls locking durability under serializable isolation. With this set to true, SELECT FOR UPDATE locks, SELECT FOR SHARED locks, and constraint check locks (e.g. locks acquired during foreign key checks if `enable_implicit_fk_locking_for_serializable` is set to true) will be guaranteed-durable under serializable isolation, meaning they will always be held to transaction commit. (These locks are always guaranteed-durable under weaker isolation levels.) By default, under serializable isolation these locks are best-effort rather than guaranteed-durable, meaning in some cases (e.g. leaseholder transfer, node loss, etc.) they could be released before transaction commit. Serializable isolation does not rely on locking for correctness, only using it to improve performance under contention, so this default is a deliberate choice to avoid the performance overhead of lock replication.
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Thanks! bors r=DrewKimball |
nvanbenschoten
approved these changes
Jul 28, 2023
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Reviewed 8 of 8 files at r1, 3 of 3 files at r2, all commit messages.
Reviewable status:
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Build failed (retrying...): |
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Build failed (retrying...): |
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Build failed: |
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The failures seem unrelated, so I'll try again. bors r=DrewKimball,nvanbenschoten |
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This PR was included in a batch that was canceled, it will be automatically retried |
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Build succeeded: |
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Follow-up from #105857
This commit ammends 6a3e43d to add a session variable to control whether guaranteed-durable locks are used under serializable isolation.
Informs: #100194
Epic: CRDB-25322
Release note (sql change): Add a new session variable,
enable_durable_locking_for_serializable, which controls locking durability under serializable isolation. With this set to true, SELECT FOR UPDATE locks, SELECT FOR SHARED locks, and constraint check locks (e.g. locks acquired during foreign key checks ifenable_implicit_fk_locking_for_serializableis set to true) will be guaranteed-durable under serializable isolation, meaning they will always be held to transaction commit. (These locks are always guaranteed-durable under weaker isolation levels.)By default, under serializable isolation these locks are best-effort rather than guaranteed-durable, meaning in some cases (e.g. leaseholder transfer, node loss, etc.) they could be released before transaction commit. Serializable isolation does not rely on locking for correctness, only using it to improve performance under contention, so this default is a deliberate choice to avoid the performance overhead of lock replication.