| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Mark Kirkwood <markir(at)paradise(dot)net(dot)nz> |
| Cc: | Josh Berkus <josh(at)agliodbs(dot)com>, Gavin Sherry <swm(at)linuxworld(dot)com(dot)au>, Jie Zhang <jzhang(at)greenplum(dot)com>, pgsql-hackers(at)postgresql(dot)org, Luke Lonergan <LLonergan(at)greenplum(dot)com> |
| Subject: | Re: On-disk bitmap index patch |
| Date: | 2006-07-27 05:14:43 |
| Message-ID: | 29908.1153977283@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Mark Kirkwood <markir(at)paradise(dot)net(dot)nz> writes:
> An obvious deduction is that the TPCH dataset is much more amenable to
> run compression than my synthetic Zipfian data was. The interesting
> question is how well "real" datasets are run compressable,
Yeah --- the back-of-the-envelope calculations I was making presupposed
uniform random distribution, and we know that's often not realistic for
real datasets. A nonuniform distribution would probably mean that some
of the bitmaps compress better-than-expected and others worse. I have
no idea how to model that and guess what the overall result is ...
regards, tom lane
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