| From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp>, Amit Khandekar <amit(dot)khandekar(at)enterprisedb(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Show lossy heap block info in EXPLAIN ANALYZE for bitmap heap scan |
| Date: | 2014-01-02 09:27:57 |
| Message-ID: | 20140102092757.GA20758@awork2.anarazel.de |
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| Lists: | pgsql-hackers |
On 2014-01-01 21:15:46 -0500, Robert Haas wrote:
> [ sensible reasoning ] However, I'm not sure it's really worth it.
> I think what people really care about is knowing whether the bitmap
> lossified or not, and generally how much got lossified. The counts of
> exact and lossy pages are sufficient for that, without anything
> additional
Showing the amount of memory currently required could tell you how soon
accurate bitmap scans will turn into lossy scans though. Which is not a
bad thing to know, some kinds of scans (e.g. tsearch over expression
indexes, postgis) can get ridiculously slow once lossy.
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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