| From: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
|---|---|
| To: | Jeff Davis <pgsql(at)j-davis(dot)com> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org, Merlin Moncure <mmoncure(at)gmail(dot)com> |
| Subject: | Re: Do we need so many hint bits? |
| Date: | 2012-11-18 14:58:16 |
| Message-ID: | CA+U5nM+Nbvjxtn43WoD8KznMAHPoMKX4mBQC_PxwERa=Y6kbQA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On 18 November 2012 08:52, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> The difference here is that we still need to check visibility of each
> tuple, but that can be a very cheap check and never involves clog, nor
> does it dirty the page. Tuple access is reasonably expensive in
> comparison with a clog-less check on tuple xmin against snapshot xmin,
> so the extra work is negligible.
The attached *partial* patch shows how the tuple checks would work.
This should fit in neatly with the vismap skip code you've got already.
Looks to me possible to skip the all-vis hint completely, as you
suggest, plus avoid repeated checks of VM or clog.
--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
| Attachment | Content-Type | Size |
|---|---|---|
| all_visible_cheap_check.v1.patch | application/octet-stream | 3.3 KB |
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