From: | Ron <ronljohnsonjr(at)gmail(dot)com> |
---|---|
To: | pgsql-general(at)lists(dot)postgresql(dot)org |
Subject: | Re: [SOLVED?] Re: Disk wait problem... not hardware... |
Date: | 2023-10-29 16:51:32 |
Message-ID: | 39d83a8e-36ef-41f7-825c-4ce290b59fd4@gmail.com |
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Lists: | pgsql-general |
On 10/29/23 11:45, pf(at)pfortin(dot)com wrote:
> On Sun, 29 Oct 2023 16:16:05 +0100 Peter J. Holzer wrote:
>
>> On 2023-10-29 09:21:46 -0400, pf(at)pfortin(dot)com wrote:
>>> These are all static tables. Does PG maintain a table row count so as to
>>> avoid having to count each time?
>> No. To count the rows in a table, Postgres has to actually read the
>> whole table (or an index, if a suitable index (e.g. a primary key)
>> exists).
> Am I correct to assume count(fieldname) would only load that column for
> counting?
The OS reads (chunks of) blocks, not individual bytes, and Postgresql is
record oriented, not column-oriented.
> In other words: we should be specific (avoid "*") in general?
No.
--
Born in Arizona, moved to Babylonia.
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