provides a means for examining what's happening in the shared
buffer cache in real time.
The module provides a C function
pg_buffercache_pages that returns a set of
records, plus a view
pg_buffercache that wraps the function for
By default use is restricted to superusers and members of the
pg_read_all_stats role. Access may
be granted to others using
The definitions of the columns exposed by the view are shown in Table F.15.
||ID, in the range 1..
||Filenode number of the relation|
||Tablespace OID of the relation|
||Database OID of the relation|
||Fork number within the relation; see
||Page number within the relation|
||Is the page dirty?|
||Clock-sweep access count|
||Number of backends pinning this buffer|
There is one row for each buffer in the shared cache. Unused
buffers are shown with all fields null except
bufferid. Shared system catalogs are shown
as belonging to database zero.
Because the cache is shared by all the databases, there will
normally be pages from relations not belonging to the current
database. This means that there may not be matching join rows
pg_class for some rows, or
that there could even be incorrect joins. If you are trying to
pg_class, it's a
good idea to restrict the join to rows having
reldatabase equal to the current
database's OID or zero.
is accessed, internal buffer manager locks are taken for long
enough to copy all the buffer state data that the view will
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=# SELECT c.relname, count(*) AS buffers FROM pg_buffercache b INNER JOIN pg_class c ON b.relfilenode = pg_relation_filenode(c.oid) AND b.reldatabase IN (0, (SELECT oid FROM pg_database WHERE 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)