Jelte Fennema-Nio <postgres@jeltef.nl> writes:
> Running "\d tablename" from psql could take multiple seconds when
> running on a system with 100k+ tables. The reason for this was that
> a sequence scan on pg_class takes place, due to regex matching being
> used.
> Regex matching is obviously unnecessary when we're looking for an exact
> match. This checks for this (common) case and starts using plain
> equality in that case.
Really? ISTM this argument is ignoring an optimization the backend
has understood for a long time.
regression=# explain select * from pg_class where relname ~ '^foo$';
QUERY PLAN
--------------------------------------------------------------------------------
-------------
Index Scan using pg_class_relname_nsp_index on pg_class (cost=0.28..8.30 rows=
1 width=739)
Index Cond: (relname = 'foo'::text)
Filter: (relname ~ '^foo$'::text)
(3 rows)
regards, tom lane