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PostgreSQL 10 Administration Cookbook - Fourth Edition
book

PostgreSQL 10 Administration Cookbook - Fourth Edition

by Simon Riggs, Gianni Ciolli
May 2018
Intermediate to advanced content levelIntermediate to advanced
576 pages
30h 25m
English
Packt Publishing
Content preview from PostgreSQL 10 Administration Cookbook - Fourth Edition

How it works…

ALTER TABLE ... ADD CONSTRAINT.. NOT VALID uses the ShareRowExclusiveLock that blocks writes and VACUUM, yet allows reads on the table to continue. The command ALTER TABLE ... VALIDATE CONSTRAINT executes using a ShareUpdateExclusiveLock that allows both reads and writes on the table yet blocks DDL and VACUUM while it scans the table.

PostgreSQL takes SQL locks according to the ISO standard, that is, locks are taken during the transaction and then released at its end. This means that algorithms like this one, where there is a short activity requiring stronger locks, followed by a longer activity that needs only lighter locks, cannot be implemented as a single command.

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Publisher Resources

ISBN: 9781788474924Supplemental Content