| From: | Daniel Kalchev <daniel(at)digsys(dot)bg> |
|---|---|
| To: | Hannu Krosing <hannu(at)tm(dot)ee> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Dann Corbit <DCorbit(at)connx(dot)com>, Steve Crawford <scrawford(at)pinpointresearch(dot)com>, pgsql-performance(at)postgresql(dot)org, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Terrible performance on wide selects |
| Date: | 2003-01-23 10:44:04 |
| Message-ID: | 200301231044.h0NAi8Y21333@dcave.digsys.bg |
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| Lists: | pgsql-hackers pgsql-performance |
>>>Hannu Krosing said:
> Tom Lane kirjutas N, 23.01.2003 kell 02:04:
> > We already do cache column offsets when they are fixed. The code that's
> > the problem executes when there's a variable-width column in the table
> > --- which means that all columns to its right are not at fixed offsets,
> > and have to be scanned for separately in each tuple, AFAICS.
>
> Not only varlen columns, but also NULL columns forbid knowing the
> offsets beforehand.
Does this mean, that constructing tables where fixed length fields are
'before' variable lenght fields and 'possibly null' fields might increase
performance?
Daniel
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