Re: Db file scattered reads vs. direct path reads

What type of filesystem are you on? What differences are there between the old system and the new apart from the storage array?

Finn

On 2/20/08, Josh Collier <Josh.Collier_at_banfield.net> wrote:
>
> Hi,
>
> I've got a conundrum. We've got a new disk system. When I full scan a
> table with the nocache hint the trace files record lots of reads like this
>
> WAIT #1: nam='db file scattered read' ela= 38471 file#=777 block#=238789
> blocks=64 obj#=2805234 tim=359927798919
>
> And the query takes 11 minutes for a 19gb table, much slower than our old
> system
>
> When I enforce direct path reads with the following parameter
> :alter session set "_serial_direct_read" = true
>
> The trace files record lots of reads like this
>
> WAIT #1: nam='direct path read' ela= 5 file number=777 first dba=238789
> block cnt=64 obj#=2805234 tim=343398354853
>
> And the query returns in 3 minutes
>
> What would cause the scattered reads to be so much slower than the direct
> path reads?
>
> I've enabled direct io on the db and verified it via truss.
>
> Version is 10.2.0.1
> Solaris 10
>
>
>
>
>
>

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