Re: buffer cache and direct reads

On Fri, 16 Jul 2004 08:00:05 -0700, utkanbir wrote:

> Hi ,
>
> i read in manual that parallel reads dont use buffer cache instead use
> pga memory . So when i issue a select statement in parallel , i expect
> to see the following things:
>
> 1. since the read is parallel , buffer cache is not used , the data is
> not cached so there will be no entry in gv$bh for the table.
> 2. gv$sessstat.name 'physical reads direct ' must be non zero .
>
> Are these correct?

No.

Parallel reads/writes are usually recovery related. Direct reads skip the buffer cache and go directly into the PGA. Thus the name. Scattered reads usually point to full scan (either table or index), while continuous reads/writes usually mean single block index I/O.

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