| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp> |
| 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: | 2013-12-07 19:48:49 |
| Message-ID: | CA+TgmoaoT-FMnMEmoaqQmnFYxx+XsswmJg_WnKfq5+tBCaYvrA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Fri, Dec 6, 2013 at 5:02 AM, Etsuro Fujita
<fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp> wrote:
> Though at first I agreed on this, while working on this I start to think information about (2) is enough for tuning work_mem. Here are examples using a version under development, where "Bitmap Memory Usage" means (peak) memory space used by a TIDBitmap, and "Desired" means the memory required to guarantee non-lossy storage of a TID set, which is shown only when the TIDBitmap has been lossified. (work_mem = 1MB.)
I'd be wary of showing a desired value unless it's highly likely to be accurate.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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