pg_buffercache view - Mailing list pgsql-admin

From Sorin N. Ciolofan
Subject pg_buffercache view
Date
Msg-id 20070424100322.7E7EE8E40FC@mailhost.ics.forth.gr
Whole thread Raw
In response to Re: [GENERAL] Increasing the shared memory  (Bill Moran <wmoran@potentialtech.com>)
Responses Re: [GENERAL] pg_buffercache view  (Bill Moran <wmoran@potentialtech.com>)
List pgsql-admin
 Dear all,

About the pg_buffercache view:
I couldn't find the description for this view in the manual at
http://www.postgresql.org/docs/8.2/interactive/catalogs.html
However I found the readme file provided in the /contrib./pg_buffercache of
the source code for version 8.2.3
Here it's written the following description:

   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?

I've 2 questions:
1)
I was not able to find the field "oid" from pg_database view. Could you
please tell me what is the actual name of the column for which reldatabase
is reffering to?
2)
In readme file is also written:
"Unused buffers are shown with all fields null except buffered".
A "used" buffer means that is used 100% or could it be filled only
partially?
Is there any way to know at a certain moment with precision how much shared
memory expressed in Mb is used?

With best regards,
Sorin




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