On Sat, Nov 24, 2012 at 11:57:51AM +0900, Satoshi Nagayasu wrote:
> Hi,
>
> I found that the manual page for pg_buffercache module explains
> "usagecount" as "Page LRU count".
>
> http://www.postgresql.org/docs/devel/static/pgbuffercache.html
>
> However, AFAIK, "usagecount" is not a LRU count nowadays, because
> LRU is no longer used for the buffer management algorithm.
>
> I think it should be described as "Clock-sweep count" or something
> like that.
>
> And I'd like to add some additional explanation for the "forknumber"
> as below:
>
> "0 for heap file, 1 for FreeSpaceMap, and 2 for VisibilityMap".
>
> Any comments?
Good suggestion. I ended up referencing the C file that contains the
"forknumber" definitions, rather than recreating the list in the docs.
I applied the attached patch to head and 9.3.
--
Bruce Momjian <[email protected]> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ It's impossible for everything to be true. +
diff --git a/doc/src/sgml/pgbuffercache.sgml b/doc/src/sgml/pgbuffercache.sgml
new file mode 100644
index 1d7d95f..685351f
*** a/doc/src/sgml/pgbuffercache.sgml
--- b/doc/src/sgml/pgbuffercache.sgml
***************
*** 84,90 ****
<entry><structfield>relforknumber</structfield></entry>
<entry><type>smallint</type></entry>
<entry></entry>
! <entry>Fork number within the relation</entry>
</row>
<row>
--- 84,91 ----
<entry><structfield>relforknumber</structfield></entry>
<entry><type>smallint</type></entry>
<entry></entry>
! <entry>Fork number within the relation; see
! <filename>include/storage/relfilenode.h</></entry>
</row>
<row>
***************
*** 98,104 ****
<entry><structfield>usagecount</structfield></entry>
<entry><type>smallint</type></entry>
<entry></entry>
! <entry>Page LRU count</entry>
</row>
</tbody>
--- 99,105 ----
<entry><structfield>usagecount</structfield></entry>
<entry><type>smallint</type></entry>
<entry></entry>
! <entry>Clock-sweep access count</entry>
</row>
</tbody>
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