How do I speed up counting rows in a PostgreSQL table?

Question

We need to count the number of rows in a PostgreSQL table. In our case, no conditions need to be met, and it would be perfectly acceptable to get a row estimate if that sig

Answer 1

Count is slow for big tables, so you can get a close estimate this way:

SELECT reltuples::bigint AS estimate 
FROM pg_class 
WHERE relname='tableName';

and its extremely fast, results are not float, but still a close estimate.

• reltuples is a column from pg_class table, it holds data about "number of rows in the table. This is only an estimate used by the planner. It is updated by VACUUM, ANALYZE, and a few DDL commands such as CREATE INDEX" (manual)
• The catalog pg_class catalogs tables and most everything else that has columns or is otherwise similar to a table. This includes indexes (but see also pg_index), sequences, views, composite types, and some kinds of special relation (manual)
• "Why is "SELECT count(*) FROM bigtable;" slow?" : http://wiki.postgresql.org/wiki/FAQ#Why_is_.22SELECT_count.28.2A.29_FROM_bigtable.3B.22_slow.3F