Re: Database I/O and other performance questions.

> 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@candle.pha.pa.us               |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026