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Clarify hash index caution and copy to CREATE INDEX docs
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doc/src/sgml/indices.sgml

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@@ -196,8 +196,10 @@ CREATE INDEX <replaceable>name</replaceable> ON <replaceable>table</replaceable>
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<para>
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Hash index operations are not presently WAL-logged,
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so hash indexes might need to be rebuilt with <command>REINDEX</>
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after a database crash. They are also not replicated over streaming or
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file-based replication.
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after a database crash if there were unwritten changes.
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Also, changes to hash indexes are not replicated over streaming or
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file-based replication after the initial base backup, so they
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give wrong anwers to queries that subsequently use them.
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For these reasons, hash index use is presently discouraged.
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</para>
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</caution>

doc/src/sgml/ref/create_index.sgml

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@@ -466,6 +466,18 @@ Indexes:
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they can be useful.
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</para>
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<caution>
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<para>
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Hash index operations are not presently WAL-logged,
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so hash indexes might need to be rebuilt with <command>REINDEX</>
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after a database crash if there were unwritten changes.
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Also, changes to hash indexes are not replicated over streaming or
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file-based replication after the initial base backup, so they
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give wrong anwers to queries that subsequently use them.
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For these reasons, hash index use is presently discouraged.
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</para>
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</caution>
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<para>
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Currently, only the B-tree, GiST and GIN index methods support
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multicolumn indexes. Up to 32 fields can be specified by default.

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