From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
---|---|
To: | Lincoln Yeoh <lyeoh(at)pop(dot)jaring(dot)my> |
Cc: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: Database I/O and other performance questions. |
Date: | 2000-12-23 14:23:49 |
Message-ID: | 200012231423.JAA14685@candle.pha.pa.us |
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Thread: | |
Lists: | pgsql-general |
> Hi everyone,
>
> What typical/max database I/O throughputs are people getting for simple
> selects of datasets cached in memory but not explicitly clustered?
> 100KB/sec? 1MB/sec? 10MB/sec? (assuming << 8KB rows).
I see transfer rates that match the I/O speed of the disk.
>
> Does a "select count(*) from tablename where ..." actually retrieve all
> columns from all the selected rows or does it only count the rows?
Yes, it reads all rows.
>
> That is to say:
> would/should select count(*) be slower than select
> count(averysmallcolumnmaybeboolean)
Same speed.
--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
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