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Re: [HACKERS] Q about heap_getattr

From: Vadim Mikheev <vadim(at)krs(dot)ru>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-hackers(at)postgreSQL(dot)org
Subject: Re: [HACKERS] Q about heap_getattr
Date: 1999-01-24 18:09:13
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Lists: pgsql-hackers
Tom Lane wrote:
> I've been doing some more backend profiling, and observe that in a large
> SELECT from a table with lots of columns, nocachegetattr (the guts of
> heap_getattr) is at the top of the list, accounting for about 15% of
> runtime.
> The percentage would be lower in a table with fewer columns or no null
> columns, but it still seems worth working on.  (Besides, this case right
> here is a real-world case for me.)
> What's drawing my eye is that printtup() is calling heap_getattr twice
> for each attribute of each tuple --- once in the first scan that
> prepares the null-fields bitmap, and then again to actually output the
> field value.  So, what I want to do is call heap_getattr only once per
> attribute and save the returned value for use in the second loop.
> That should halve the time spent in nocachegetattr and thus knock
> 7 or so percent off the runtime of SELECT.

Try to use heap_attisnull in first scan!
This func just tests nulls bitmap array of tuple...

P.S. Tom, I forgot to attach new allocation code in my prev letter,
but now I want to reimplement them.

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