Add hash index caution to CREATE INDEX docs

diff --git a/doc/src/sgml/ref/create_index.sgml b/doc/src/sgml/ref/create_index.sgml
index 5104a656e9ef02f1b64475f7bcd9e279eb4967db..400450460de06174c615e44d00378f03fd9db95a 100644 (file)
--- a/doc/src/sgml/ref/create_index.sgml
+++ b/doc/src/sgml/ref/create_index.sgml
@@ -428,6 +428,18 @@ Indexes:
    they can be useful.
   </para>
 
+  <caution>
+   <para>
+    Hash index operations are not presently WAL-logged,
+    so hash indexes might need to be rebuilt with <command>REINDEX</>
+    after a database crash if there were unwritten changes.
+    Also, changes to hash indexes are not replicated over warm standby
+    replication after the initial base backup, so they
+    give wrong anwers to queries that subsequently use them.
+    For these reasons, hash index use is presently discouraged.
+   </para>
+  </caution>
+
   <para>
    Currently, only the B-tree, GiST and GIN index methods support
    multicolumn indexes. Up to 32 fields can be specified by default.