| From: | Hannu Krosing <hannu(at)tm(dot)ee> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | 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 10:30:48 |
| Message-ID: | 1043317847.2347.35.camel@localhost.localdomain |
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| Lists: | pgsql-hackers pgsql-performance |
Tom Lane kirjutas N, 23.01.2003 kell 02:04:
> "Dann Corbit" <DCorbit(at)connx(dot)com> writes:
> > Maybe I don't really understand the problem, but it seems simple enough
> > to do it once for the whole query.
>
> 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.
--
Hannu Krosing <hannu(at)tm(dot)ee>
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