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7th chunk of `doc/src/sgml/pgbuffercache.sgml`
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 and the number of
   buffers that could not be evicted.  Flushed buffers haven't necessarily
   been flushed by us, they might have been flushed by someone else.  The
   result is immediately out of date upon return, as buffers might immediately
   be read back in due to concurrent activity.  The function is intended for
   developer testing only.
  </para>
 </sect2>

 <sect2 id="pgbuffercache-pg-buffercache-evict-all">
  <title>The <structname>pg_buffercache_evict_all</structname> Function</title>
  <para>
   The <function>pg_buffercache_evict_all()</function> function is very
   similar to the <function>pg_buffercache_evict()</function> function.  The
   difference is, the <function>pg_buffercache_evict_all()</function> function
   does not take an argument; instead it tries to evict all buffers in the
   buffer pool.  It returns the number of evicted buffers, flushed buffers and
   the number of buffers that could not be evicted.  Flushed buffers haven't
   necessarily been flushed by us, they might have been flushed by someone
   else.  The result is immediately out of date upon return, as buffers might
   immediately be read back in due to concurrent activity.  The function is
   intended for developer testing only.
  </para>
 </sect2>

<sect2 id="pgbuffercache-sample-output">
  <title>Sample Output</title>

<screen>
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)


regression=# SELECT * FROM pg_buffercache_summary();
 buffers_used | buffers_unused | buffers_dirty | buffers_pinned | usagecount_avg
--------------+----------------+---------------+----------------+----------------
          248 |        2096904 |            39 |              0 |       3.141129
(1 row)


regression=# SELECT * FROM pg_buffercache_usage_counts();
 usage_count | buffers | dirty | pinned
-------------+---------+-------+--------
           0 |   14650 |     0 |      0
           1 |    1436 |   671 |      0
           2 |     102 |    88 |      0
           3 |      23 |    21 |      0
           4 |       9 |     7 |      0
           5 |     164 |   106 |      0
(6 rows)
</screen>
 </sect2>

 <sect2 id="pgbuffercache-authors">
  <title>Authors</title>

  <para>
   Mark Kirkwood <email>markir@paradise.net.nz</email>
  </para>

  <para>
   Design suggestions: Neil Conway <email>neilc@samurai.com</email>
  </para>

  <para>
   Debugging advice: Tom Lane <email>tgl@sss.pgh.pa.us</email>
  </para>
 </sect2>

</sect1>
Title: pg_buffercache Module
Summary
The pg_buffercache module provides functions to evict buffers from the buffer pool, including pg_buffercache_evict(), pg_buffercache_evict_relation(), and pg_buffercache_evict_all(), as well as views to summarize buffer usage, such as pg_buffercache_summary() and pg_buffercache_usage_counts(), with example queries and output, and credits to the authors who contributed to the module, including Mark Kirkwood, Neil Conway, and Tom Lane.