Re: Slow count(*) again...

  On 10/10/2010 8:27 PM, Joshua Tolley wrote:
> It was asserted that reading bigger chunks would help performance; a response
> suggested that, at least in Linux, setting readahead on a device would
> essentially do the same thing. Or that's what I got from the thread, anyway.
> I'm interested to know how similar performance might be between the large
> block size case and the large readahead case. Comments, anyone?
>

Craig maybe right, the fact that Oracle is doing direct I/O probably 
does account for the difference. The fact is, however, that the question 
about slow sequential scan appears with some regularity on PostgreSQL 
forums. My guess that a larger chunk would be helpful may not be 
correct, but I do believe that there is a problem with a too slow 
sequential scan.  Bigger chunks are a very traditional solution which 
may not work but the problem is still there.

-- 
Mladen Gogala
Sr. Oracle DBA
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