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docs: Changing column type doesn't always require an index rebuild.

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James Coleman and Robert Haas, reviewed by Matthias van de Meent.

Discussion: https://postgr.es/m/CAAaqYe90Ea3RG=A7H-ONvTcx549-oQhp07BrHErwM=AyH2ximg@mail.gmail.com
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Robert Haas 2022-04-01 08:48:44 -04:00
parent af9e180495
commit fa25bebb82
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doc/src/sgml/ref/alter_table.sgml
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@ -1366,7 +1366,13 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
existing column, if the <literal>USING</literal> clause does not change
the column contents and the old type is either binary coercible to the new
type or an unconstrained domain over the new type, a table rewrite is not
needed; but any indexes on the affected columns must still be rebuilt.
needed. However, indexes must always be rebuilt unless the system can
verify that the new index would be logically equivalent to the existing
one. For example, if the collation for a column has been changed an index
rebuild is always required because the new sort order might be different.
However, in the absence of a collation change, a column can be changed
from <type>text</type> to <type>varchar</type> (or vice versa) without
rebuilding the indexes because these data types sort identically.
Table and/or index rebuilds may take a
significant amount of time for a large table; and will temporarily require
as much as double the disk space.