| From: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
|---|---|
| To: | Jack Douglas <jack(at)douglastechnology(dot)co(dot)uk> |
| Cc: | 'Tom Lane' <tgl(at)sss(dot)pgh(dot)pa(dot)us>, 'Martijn van Oosterhout' <kleptog(at)svana(dot)org>, pgsql-general(at)postgresql(dot)org |
| Subject: | Re: new index type with clustering in mind. |
| Date: | 2014-12-10 19:42:13 |
| Message-ID: | 20141210194213.GA1768@alvh.no-ip.org |
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| Thread: | |
| Lists: | pgsql-general |
Jack Douglas wrote:
> > in 9.4, GIN indexes are pretty close to this already
>
> Do I understand correctly that BRIN indexes will be even closer to this?
>
Yeah, in a way. You could say they are closer from the opposite end.
There is one index tuple in a BRIN index for each page range (contiguous
set of pages); each index tuple contains a "summary" of what in that
page range. There are no exact entries. If the values are randomly
scattered, the index is useless; all page ranges will have to be scanned
for possibly matching tuples. If the values are perfectly clustered,
the index is optimal because you scan the minimal set of pages.
--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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