In my test all 3358604 rows were inserted by single 'COPY FROM file' command. So it's obviously that each row has only one version. > For 8.2 onwards, the tuple header is > 23 bytes. Add another 4 bytes for one line pointer for each row. If you > have > null values, another 5 bytes for null bitmap and alignment. Plus add few > bytes > for page header and any unusable space in a page (because a row can not > fit in the remaining space). > Simple calculations show that each row occupies 76 bytes approximately. > But anticipated row size would be 41 or near. Row overhead: 23 + 4 + 5 = 32 Total row size: 32 + 41 = 73 Unfortunately value '76' has an objective explanation. Thanks, Sergey Zubkovsky -----Original Message----- From: Adrian Klaver [mailto:aklaver@xxxxxxxxxxx] Sent: Thursday, March 20, 2008 5:44 PM To: pgsql-general@xxxxxxxxxxxxxx Cc: Zubkovsky, Sergey; Pavan Deolasee Subject: Re: Row size overhead On Thursday 20 March 2008 7:24 am, Zubkovsky, Sergey wrote: > Thanks for your reply. > > I had used PG 8.3.1 on 32-bit WinXP platform. > "PostgreSQL 8.3.1, compiled by Visual C++ build 1400" > But I suppose this fact doesn't change anything essentially. > > Thanks, > Sergey Zubkovsky What you are probably seeing is row depth not row width. Postgres uses MVCC and so there can be multiple versions of a row in existence at one time. For a better explanation see: http://www.postgresql.org/docs/8.3/interactive/routine-vacuuming.html Try running Vacuum and/or Vacuum Full and see what happens to table size. > > > -----Original Message----- > From: Pavan Deolasee [mailto:pavan.deolasee@xxxxxxxxx] > Sent: Wednesday, March 19, 2008 8:23 PM > To: Zubkovsky, Sergey > Cc: pgsql-general@xxxxxxxxxxxxxx > Subject: Re: Row size overhead > > 2008/3/19 Zubkovsky, Sergey <Sergey.Zubkovsky@xxxxxxxxxxx>: > > Simple calculations show that each row occupies 76 bytes > > approximately. > > > But anticipated row size would be 41 or near. > > You haven't mentioned PG version. For 8.2 onwards, the tuple header is > 23 bytes. Add another 4 bytes for one line pointer for each row. If you > have > null values, another 5 bytes for null bitmap and alignment. Plus add few > bytes > for page header and any unusable space in a page (because a row can not > fit in the remaining space). > > Also ISTM that you might be loosing some space because of alignment > in the tuple itself. Try moving booleans and char(3) at the end. There > is not > much you can do with other overheads. > > > Thanks, > Pavan > > > > -- > Pavan Deolasee > EnterpriseDB http://www.enterprisedb.com -- Adrian Klaver aklaver@xxxxxxxxxxx -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
