Re: Single block reads instead of multiblock reads
- From: LS Cheng <exriscer@xxxxxxxxx>
- To: kennethnaim@xxxxxxxxx
- Date: Wed, 18 Aug 2010 09:38:42 +0200
Hi
AFIAK if a FTS shows single block reads it is because some blocks are
already in the buffer cache therefore there is no need to re-read using
scatter read
Thanks
--
LSC
On Wed, Aug 18, 2010 at 7:16 AM, Kenneth Naim <kennethnaim@xxxxxxxxx> wrote:
> I have a query that needs to read 25% of a 100gb (116 million row, 600
> columns) table which has been recently analyzed. The database is 11.1.0.7,
> sga is 35gb, pga 15gb, solaris, 16 cpus, 16k blocksize.
>
>
>
> The query only accesses one table. When run single threaded or in parallel
> the query runs for hours with the top wait event being db file sequential
> read not sequential reads with the p3 showing 1 block. I have checked the
> explain plan, rowsource in a tkrpof-ed trace file, the v$sql_plan all show
> full table scan. I’ve specified a full hint with the correct alias and I’m
> at a loss on why I’m not seeing a multiblock read.
>
>
>
> I’ve even simplified the case to be ctas * from big_table where
> rownum<1000000 and it still does single block reads.
>
>
>
> Anyone has ideas to why this could be happening?
>
>
>
> Ken
>
>
>
>
>
>
>
Other related posts:
