| From: | Jeff Davis <pgsql(at)j-davis(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Noah Misch <noah(at)leadboat(dot)com>, pgsql-hackers(at)postgresql(dot)org, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
| Subject: | Re: 9.3: load path to mitigate load penalty for checksums |
| Date: | 2012-06-12 22:26:25 |
| Message-ID: | 1339539985.12295.71.camel@sussancws0025 |
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| Lists: | pgsql-hackers |
On Tue, 2012-06-12 at 18:02 -0400, Tom Lane wrote:
> Or (d) it's not a problem, since the inserting XID is still busy
> according to the readers' snapshots.
How much of a savings did we get from PD_ALL_VISIBLE when it was added
into the page-at-a-time visibility check?
>From 608195a3a3656145a7eec7a47d903bc684011d73:
"In addition to the visibility map, there's a new PD_ALL_VISIBLE flag on
each heap page, also indicating that all tuples on the page are visible
to all transactions. It's important that this flag is kept up-to-date.
It is also used to skip visibility tests in sequential scans, which
gives a small performance gain on seqscans."
If "small" means that it's something we can give up, then focusing on
HEAP_XMIN_COMMITTED makes sense. But if we can't give it up, then we
need to take it into account in the proposal.
Regards,
Jeff Davis
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