Hash index operations are not presently WAL-logged,
so hash indexes might need to be rebuilt with REINDEX>
- after a database crash. They are also not replicated over streaming or
- file-based replication.
+ after a database crash if there were unwritten changes.
+ Also, changes to hash indexes are not replicated over streaming or
+ file-based 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.
they can be useful.
+
+ Hash index operations are not presently WAL-logged,
+ so hash indexes might need to be rebuilt with REINDEX>
+ after a database crash if there were unwritten changes.
+ Also, changes to hash indexes are not replicated over streaming or
+ file-based 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.
+
+
+
Currently, only the B-tree, GiST and GIN index methods support
multicolumn indexes. Up to 32 fields can be specified by default.