From 46651ce6fe013220ed397add242004d764fc0153 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sat, 4 May 2024 14:15:05 +0200 Subject: Adding upstream version 14.5. Signed-off-by: Daniel Baumann --- doc/src/sgml/pgbuffercache.sgml | 213 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 213 insertions(+) create mode 100644 doc/src/sgml/pgbuffercache.sgml (limited to 'doc/src/sgml/pgbuffercache.sgml') diff --git a/doc/src/sgml/pgbuffercache.sgml b/doc/src/sgml/pgbuffercache.sgml new file mode 100644 index 0000000..e68d159 --- /dev/null +++ b/doc/src/sgml/pgbuffercache.sgml @@ -0,0 +1,213 @@ + + + + pg_buffercache + + + pg_buffercache + + + + The pg_buffercache module provides a means for + examining what's happening in the shared buffer cache in real time. + + + + pg_buffercache_pages + + + + 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 + convenient use. + + + + By default, use is restricted to superusers and members of the + pg_monitor role. Access may be granted to others + using GRANT. + + + + The <structname>pg_buffercache</structname> View + + + The definitions of the columns exposed by the view are shown in . + + + + <structname>pg_buffercache</structname> Columns + + + + + Column Type + + + Description + + + + + + + + bufferid integer + + + ID, in the range 1..shared_buffers + + + + + + relfilenode oid + (references pg_class.relfilenode) + + + Filenode number of the relation + + + + + + reltablespace oid + (references pg_tablespace.oid) + + + Tablespace OID of the relation + + + + + + reldatabase oid + (references pg_database.oid) + + + Database OID of the relation + + + + + + relforknumber smallint + + + Fork number within the relation; see + common/relpath.h + + + + + + relblocknumber bigint + + + Page number within the relation + + + + + + isdirty boolean + + + Is the page dirty? + + + + + + usagecount smallint + + + Clock-sweep access count + + + + + + pinning_backends integer + + + 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 in pg_class for + some rows, or that there could even be incorrect joins. If you are + trying to join against pg_class, it's a good idea to + restrict the join to rows having reldatabase equal to + the current database's OID or zero. + + + + Since buffer manager locks are not taken to copy the buffer state data that + the view will display, accessing pg_buffercache view + has less impact on normal buffer activity but it doesn't provide a consistent + set of results across all buffers. However, we ensure that the information of + each buffer is self-consistent. + + + + + Sample Output + + +regression=# SELECT n.nspname, c.relname, count(*) AS buffers + FROM pg_buffercache b 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())) + JOIN pg_namespace n ON n.oid = c.relnamespace + GROUP BY n.nspname, c.relname + ORDER BY 3 DESC + LIMIT 10; + + nspname | relname | buffers +------------+------------------------+--------- + public | delete_test_table | 593 + public | delete_test_table_pkey | 494 + pg_catalog | pg_attribute | 472 + public | quad_poly_tbl | 353 + public | tenk2 | 349 + public | tenk1 | 349 + public | gin_test_idx | 306 + pg_catalog | pg_largeobject | 206 + public | gin_test_tbl | 188 + public | spgist_text_tbl | 182 +(10 rows) + + + + + Authors + + + Mark Kirkwood markir@paradise.net.nz + + + + Design suggestions: Neil Conway neilc@samurai.com + + + + Debugging advice: Tom Lane tgl@sss.pgh.pa.us + + + + -- cgit v1.2.3