cherrypick-2.0: sql, kv: use Delete instead of DeleteRange to lessen impact on tscache #23289
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…impact on tscache Previously, on the slow path for deletion from SQL, rows were deleted using a call to `DeleteRange` in order to remove all column families with a single statement. It turns out this is better done using one call per column family to `Delete`. `DeleteRange` must update the write timestamp cache in order to avoid lost update anomalies. By lessening the pressure on the timestamp cache, we can avoid pushing a transaction's commit timestamp forward and triggering a retry. This allow substantially longer / larger `DELETE FROM` statements to run to completion, assuming there is no other concurrency which will force a retry. In conjunction, a realization from cockroachdb#21165 was that large `DELETE FROM` statements can end up running forever. This occurs because they are retryable from the SQL executor and continue to get retryable errors due to the timestamp cache being unable to avoid pushing their timestamps forward. Release note (sql change): will fix endless churn experienced from large `DELETE FROM` statements, either by allowing them to complete, or by exiting with an error message indicating the transaction is too large to complete.
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spencerkimball
changed the title
bdarnell
approved these changes
Mar 1, 2018
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Previously, on the slow path for deletion from SQL, rows were deleted
using a call to
DeleteRangein order to remove all column familieswith a single statement. It turns out this is better done using one
call per column family to
Delete.DeleteRangemust update thewrite timestamp cache in order to avoid lost update anomalies. By
lessening the pressure on the timestamp cache, we can avoid pushing
a transaction's commit timestamp forward and triggering a retry. This
allow substantially longer / larger
DELETE FROMstatements to runto completion, assuming there is no other concurrency which will force
a retry.
In conjunction, a realization from #21165 was that large
DELETE FROMstatements can end up running forever. This occurs because they are
retryable from the SQL executor and continue to get retryable errors
due to the timestamp cache being unable to avoid pushing their
timestamps forward.
Release note (sql change): will fix endless churn experienced from
large
DELETE FROMstatements, either by allowing them to complete,or by exiting with an error message indicating the transaction is too
large to complete.