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doc: clarify when expression indexes evaluate their expressions
2021年12月22日 21:29:16 +0000 (16:29 -0500)
2021年12月22日 21:29:16 +0000 (16:29 -0500)
Only non-HOT updates evaluate the index expression.

Reported-by: Chris Lowder
Discussion: https://postgr.es/m/163967385701.26064.15365003480975321072@wrigleys.postgresql.org

Backpatch-through: 10


diff --git a/doc/src/sgml/indices.sgml b/doc/src/sgml/indices.sgml
index 56fbd45178362a2ac43958058d6b43fee1c66b20..023157d8884e98b0c8aaf4e90ffd215ef11dc6c9 100644 (file)
--- a/doc/src/sgml/indices.sgml
+++ b/doc/src/sgml/indices.sgml
@@ -748,8 +748,8 @@ CREATE INDEX people_names ON people ((first_name || ' ' || last_name));
<para>
Index expressions are relatively expensive to maintain, because the
- derived expression(s) must be computed for each row upon insertion
- and whenever it is updated. However, the index expressions are
+ derived expression(s) must be computed for each row insertion
+ and non-HOT update. However, the index expressions are
<emphasis>not</emphasis> recomputed during an indexed search, since they are
already stored in the index. In both examples above, the system
sees the query as just <literal>WHERE indexedcolumn = 'constant'</literal>
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