| From: | "Etsuro Fujita" <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp> |
|---|---|
| To: | "'Etsuro Fujita'" <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp>, "'Robert Haas'" <robertmhaas(at)gmail(dot)com> |
| Cc: | "'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: | 2013-12-27 06:47:44 |
| Message-ID: | 001f01cf02cf$8c3d09d0$a4b71d70$@etsuro@lab.ntt.co.jp |
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| Lists: | pgsql-hackers |
> I wrote:
> > Robert Haas wrote:
> > > I'd be wary of showing a desired value unless it's highly likely to
> > > be accurate.
> > The desired value is accurately estimated based on (a) the total
> > number of exact/lossy pages stored in the TIDBitmap and (b) the
> > following equation in tbm_create(), except for the GIN case where
> > lossy pages are added to the TIDBitmap by tbm_add_page().
I've found there is another risk of overestimating the desired memory space
for a BitmapAnded TIDBitmap. I'm inclined to get rid of the estimation
functionality from the patch completely, and leave it for future work.
Attached is a new version of the patch, which shows only fetch block
information and memory usage information. I'll add this to the upcoming CF.
Thanks,
Best regards,
Etsuro Fujita
| Attachment | Content-Type | Size |
|---|---|---|
| explain-bitmapscan-20131227.patch | application/octet-stream | 7.4 KB |
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