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Make an editorial pass over the newly SGML-ified contrib documentation.

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Fix lots of bad markup, bad English, bad explanations.

Second round of commits.  pgcrypto and pgstandby still to go...
This commit is contained in:
Tom Lane
2007-12-10 05:32:51 +00:00
parent a3102ce1ef
commit 8828689ae9
12 changed files with 2351 additions and 2003 deletions
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doc/src/sgml/pgbuffercache.sgml
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@@ -1,85 +1,138 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/pgbuffercache.sgml,v 2.2 2007/12/10 05:32:51 tgl Exp $ -->
<sect1 id="pgbuffercache">
<title>pg_buffercache</title>
<indexterm zone="pgbuffercache">
<primary>pg_buffercache</primary>
</indexterm>
<para>
The <literal>pg_buffercache</literal> module provides a 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.
The <filename>pg_buffercache</filename> module provides a means for
examining what's happening in the shared buffer cache in real time.
</para>
<para>
This module consists of a C function <literal>pg_buffercache_pages()</literal>
that returns a set of records, plus a view <literal>pg_buffercache</literal>
to wrapper the function.
The module provides a C function <function>pg_buffercache_pages</function>
that returns a set of records, plus a view
<structname>pg_buffercache</structname> that wraps the function for
convenient use.
</para>
<para>
By default public access is REVOKED from both of these, just in case there
By default public access is revoked from both of these, just in case there
are security issues lurking.
</para>
<sect2>
<title>Notes</title>
<title>The <structname>pg_buffercache</structname> view</title>
<para>
The definition of the columns exposed in the view is:
The definitions of the columns exposed by the view are:
</para>
<programlisting>
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
</programlisting>
<table>
<title><structname>pg_buffercache</> Columns</title>
<tgroup cols="4">
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>References</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><structfield>bufferid</structfield></entry>
<entry><type>integer</type></entry>
<entry></entry>
<entry>ID, in the range 1..<varname>shared_buffers</></entry>
</row>
<row>
<entry><structfield>relfilenode</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal>pg_class.relfilenode</literal></entry>
<entry>Relfilenode of the relation</entry>
</row>
<row>
<entry><structfield>reltablespace</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal>pg_tablespace.oid</literal></entry>
<entry>Tablespace OID of the relation</entry>
</row>
<row>
<entry><structfield>reldatabase</structfield></entry>
<entry><type>oid</type></entry>
<entry><literal>pg_database.oid</literal></entry>
<entry>Database OID of the relation</entry>
</row>
<row>
<entry><structfield>relblocknumber</structfield></entry>
<entry><type>bigint</type></entry>
<entry></entry>
<entry>Page number within the relation</entry>
</row>
<row>
<entry><structfield>isdirty</structfield></entry>
<entry><type>boolean</type></entry>
<entry></entry>
<entry>Is the page dirty?</entry>
</row>
<row>
<entry><structfield>usagecount</structfield></entry>
<entry><type>smallint</type></entry>
<entry></entry>
<entry>Page LRU count</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
There is one row for each buffer in the shared cache. Unused buffers are
shown with all fields null except bufferid.
shown with all fields null except <structfield>bufferid</>. Shared system
catalogs are shown as belonging to database zero.
</para>
<para>
Because the cache is shared by all the databases, there are pages from
relations not belonging to the current database.
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 <structname>pg_class</> for
some rows, or that there could even be incorrect joins. If you are
trying to join against <structname>pg_class</>, it's a good idea to
restrict the join to rows having <structfield>reldatabase</> equal to
the current database's OID or zero.
</para>
<para>
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
When the <structname>pg_buffercache</> view 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.
</para>
</sect2>
<sect2>
<title>Sample output</title>
<programlisting>
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())
FROM pg_buffercache b INNER JOIN pg_class c
ON b.relfilenode = c.relfilenode 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
@@ -95,26 +148,23 @@
pg_depend | 22
pg_depend_reference_index | 20
(10 rows)
regression=#
</programlisting>
</sect2>
<sect2>
<title>Authors</title>
<itemizedlist>
<listitem>
<para>
Mark Kirkwood <email>markir@paradise.net.nz</email>
</para>
</listitem>
<listitem>
<para>Design suggestions: Neil Conway <email>neilc@samurai.com</email></para>
</listitem>
<listitem>
<para>Debugging advice: Tom Lane <email>tgl@sss.pgh.pa.us</email></para>
</listitem>
</itemizedlist>
<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>