| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Heikki Linnakangas <heikki(at)enterprisedb(dot)com> |
| Cc: | Patches <pgsql-patches(at)postgresql(dot)org>, Jeff Davis <pgsql(at)j-davis(dot)com> |
| Subject: | Re: Synchronized scans |
| Date: | 2007-06-04 14:20:20 |
| Message-ID: | 18851.1180966820@sss.pgh.pa.us |
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| Lists: | pgsql-patches |
Heikki Linnakangas <heikki(at)enterprisedb(dot)com> writes:
> For the record, this patch has a small negative impact on scans like
> "SELECT * FROM foo LIMIT 1000". If such a scan is run repeatedly, in CVS
> HEAD the first 1000 rows will stay in buffer cache, but with the patch
> each scan will start from roughly where previous one stopped, requiring
> more pages to be read from disk each time. I don't think it's something
> to worry about in practice, but I thought I'd mention it.
Urgh. The answers change depending on (more or less) the phase of the
moon? I've got a serious problem with that. You might look back to
1997 when GEQO very nearly got tossed out entirely because it destroyed
reproducibility of query results.
regards, tom lane
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