From: | "Luke Lonergan" <llonergan(at)greenplum(dot)com> |
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To: | "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "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 |
Subject: | Re: On-disk bitmap index patch |
Date: | 2006-07-27 03:55:38 |
Message-ID: | C0ED874A.2AFBB%llonergan@greenplum.com |
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Tom,
On 7/26/06 7:26 AM, "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> I wonder
> whether they oughtn't use 16-bit instead of 8-bit HRL_WORDs
We tried variations from 8-bit to 32-bit and came to the conclusion that
8-bit was a better match for the more general case. For the moment I forget
exactly why (maybe Jie or Ayush will recall). It's a #define I believe, so
you can play with it to find out.
There's a lot more to be done with this - I think we've got some big gains
ahead.
BTW - lots of excitement here at OSCON about bitmap index, and there's a
fellow who is using the current Bizgres version, but wants *higher*
cardinality support, so I discussed Jie's thoughts about implementing
binning on values, basically combining bit vectors into value bins as the
cardinality increases.
I am still puzzled why our index creation time increases so dramatically as
we approach cardinality 10,000. I know that we found that index page
traversal for append began to take a lot of time as we started to increase
the number of bitvector pages - we had talked about aggregating the append
operations into groups before they were implemented to sequentialize the
access.
- Luke
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