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Commit8ac700a

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doc: Clarify behavior of query planner locking with REINDEX
The documentation of REINDEX has never mentioned that the query plannermay take an ACCESS SHARE lock on the indexes depending on the queryused. This adds also a note about prepared queries not impacted whenthey do not use the index(es) rebuilt.Author: Frédéric YhuelReviewed-by: Guillaume Lelarge, Justin PryzbyDiscussion:https://postgr.es/m/65d08718-6f11-978a-4b5a-72b807d4c663@dalibo.com
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‎doc/src/sgml/ref/reindex.sgml

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@@ -275,7 +275,12 @@ REINDEX [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] { IN
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considerations are rather different. <command>REINDEX</command> locks out writes
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but not reads of the index's parent table. It also takes an
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<literal>ACCESS EXCLUSIVE</literal> lock on the specific index being processed,
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which will block reads that attempt to use that index. In contrast,
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which will block reads that attempt to use that index. In particular,
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the query planner tries to take an <literal>ACCESS SHARE</literal>
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lock on every index of the table, regardless of the query, and so
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<command>REINDEX</command> blocks virtually any queries except for some
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prepared queries whose plan has been cached and which don't use this very
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index. In contrast,
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<command>DROP INDEX</command> momentarily takes an
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<literal>ACCESS EXCLUSIVE</literal> lock on the parent table, blocking both
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writes and reads. The subsequent <command>CREATE INDEX</command> locks out

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