Re: [SOLVED?] Re: Disk wait problem... not hardware...

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.