Обсуждение: Does Postgres compress data?
If I run this query: select sum(length(html)) from Indexer.Pages; I get: 15,680,005,116 However, if I type: C:\Program Files\PostgreSQL>dir /s I get: Total Files Listed: 5528 File(s) 7,414,385,333 bytes 575 Dir(s) 43,146,137,600 bytes free So all the Postgres data on disk is a little over 7 gigs, however the total sum of bytes in the HTML column of the Pages table is over 15 gigs. Is PG compressing this data? I'm curious as I was considering converting this column to a byte array and gzip'ing the data to save space, however if PG is already doing this for me, then I'm not going to bother. Thanks! Mike
On 05/23/2012 06:07 PM, Mike Christensen wrote: > If I run this query: > > select sum(length(html)) from Indexer.Pages; > > I get: > > 15,680,005,116 > > However, if I type: > > C:\Program Files\PostgreSQL>dir /s > > I get: > > Total Files Listed: > 5528 File(s) 7,414,385,333 bytes > 575 Dir(s) 43,146,137,600 bytes free > > So all the Postgres data on disk is a little over 7 gigs, however the > total sum of bytes in the HTML column of the Pages table is over 15 > gigs. > > Is PG compressing this data? I'm curious as I was considering > converting this column to a byte array and gzip'ing the data to save > space, however if PG is already doing this for me, then I'm not going > to bother. Thanks! Yes. See here for complete answer: http://www.postgresql.org/docs/9.1/static/storage-toast.html > > Mike > -- Adrian Klaver adrian.klaver@gmail.com
Mike -- <...> > >Is PG compressing this data? I'm curious as I was considering >converting this column to a byte array and gzip'ing the data to save >space, however if PG is already doing this for me, then I'm not going >to bother. Thanks! > >Mike It may vary from version of postgres to version, but perhaps you are seeing the effects of TOAST kicking in ? Do a searchin the documentation for your specific version (8.3, 9.1 etc.) HTH, Greg Williamson
On Wed, May 23, 2012 at 6:16 PM, Greg Williamson <gwilliamson39@yahoo.com> wrote: > Mike -- > > > <...> > >> >>Is PG compressing this data? I'm curious as I was considering >>converting this column to a byte array and gzip'ing the data to save >>space, however if PG is already doing this for me, then I'm not going >>to bother. Thanks! >> >>Mike > > > It may vary from version of postgres to version, but perhaps you are seeing the effects of TOAST kicking in ? Do a searchin the documentation for your specific version (8.3, 9.1 etc.) Yup, looks like this is the default behavior for TOAST-able columns. I'm running on 9.0. Anyway, good information - I was mostly just curious.. Mike