| From: | Peter Geoghegan <pg(at)heroku(dot)com> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | "ktm(at)rice(dot)edu" <ktm(at)rice(dot)edu>, Tan Tran <tankimtran(at)gmail(dot)com>, Greg Stark <stark(at)mit(dot)edu>, pgsql-advocacy <pgsql-advocacy(at)postgresql(dot)org>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: [HACKERS] GSoC on WAL-logging hash indexes |
| Date: | 2014-04-30 18:02:56 |
| Message-ID: | CAM3SWZQYmqdASR=xNgLZHgGngA29g_1ngOTDv=pHJ3vTj0sAgA@mail.gmail.com |
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On Wed, Apr 30, 2014 at 10:11 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> I thought the theoretical advantage of hash indexes wasn't that they
> were smaller but that you avoided a central contention point (the
> btree root).
The B-Tree root isn't really a central contention point at all. The
locking/latching protocol that nbtree uses is remarkably
concurrency-friendly. In the real world, there is pretty much no
exclusive locking of the root page's buffer.
> Of course our current hash indexes have *more* not less contention
> than btree but I'm pretty comfortable chalking that up to quality of
> implementation rather than anything intrinsic.
I am not convinced of that.
--
Peter Geoghegan
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