pg_buffercache pg_buffercache module provides the means for examining what's happening to the buffercache at any given time without having to restart or rebuild the server with debugging code added. The intent is to do for the buffercache what pg_locks does for locks. This module consists of a C function pg_buffercache_pages() that returns a set of records, plus a view pg_buffercache to wrapper the function. By default public access is REVOKED from both of these, just in case there are security issues lurking. The definition of the columns exposed in the view is: Column | references | Description ----------------+----------------------+------------------------------------ bufferid | | Id, 1..shared_buffers. relfilenode | pg_class.relfilenode | Refilenode of the relation. reltablespace | pg_tablespace.oid | Tablespace oid of the relation. reldatabase | pg_database.oid | Database for the relation. relblocknumber | | Offset of the page in the relation. isdirty | | Is the page dirty? usagecount | | Page LRU count There is one row for each buffer in the shared cache. Unused buffers are shown with all fields null except bufferid. Because the cache is shared by all the databases, there are pages from relations not belonging to the current database. When the pg_buffercache view is accessed, internal buffer manager locks are taken, and a copy of the buffer cache data is made for the view to display. This ensures that the view produces a consistent set of results, while not blocking normal buffer activity longer than necessary. Nonetheless there could be some impact on database performance if this view is read often. regression=# \d pg_buffercache; View "public.pg_buffercache" Column | Type | Modifiers ----------------+----------+----------- bufferid | integer | relfilenode | oid | reltablespace | oid | reldatabase | oid | relblocknumber | bigint | isdirty | boolean | usagecount | smallint | View definition: SELECT p.bufferid, p.relfilenode, p.reltablespace, p.reldatabase, p.relblocknumber, p.isdirty, p.usagecount FROM pg_buffercache_pages() p(bufferid integer, relfilenode oid, reltablespace oid, reldatabase oid, relblocknumber bigint, isdirty boolean, usagecount smallint); regression=# SELECT c.relname, count(*) AS buffers FROM pg_class c INNER JOIN pg_buffercache b ON b.relfilenode = c.relfilenode INNER JOIN pg_database d ON (b.reldatabase = d.oid AND d.datname = current_database()) GROUP BY c.relname ORDER BY 2 DESC LIMIT 10; relname | buffers ---------------------------------+--------- tenk2 | 345 tenk1 | 141 pg_proc | 46 pg_class | 45 pg_attribute | 43 pg_class_relname_nsp_index | 30 pg_proc_proname_args_nsp_index | 28 pg_attribute_relid_attnam_index | 26 pg_depend | 22 pg_depend_reference_index | 20 (10 rows) regression=# Mark Kirkwood markir@paradise.net.nz Design suggestions: Neil Conway neilc@samurai.com Debugging advice: Tom Lane tgl@sss.pgh.pa.us