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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

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The good thing about the aforementioned recipe is that it returns a value in about the same time, no matter how big the table is. The bad thing about it is that pg_relation_size() requests a lock on the table, so if any other user has an AccessExclusiveLock lock on the table, then the table size estimate will wait for the lock to be released before returning a value.

Err... so what is an AccessExclusiveLock lock? While performing a SQL maintenance action, such as changing the data type of a column, PostgreSQL will lock out all other actions on that table, including pg_relation_size, which takes a lock in the AccessShareLock mode. For me, a typical case is when I issue some form of SQL maintenance action, such as ALTER TABLE ...

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Publisher Resources

ISBN: 9781788474924Supplemental Content