Re: row cache lock contention parallel insert

  • From: LS Cheng <exriscer@xxxxxxxxx>
  • To: Greg Rahn <greg@xxxxxxxxxxxxxxxxxx>
  • Date: Sat, 19 Dec 2009 19:06:57 +0100


I have done that already but still. But I just find out the possible cause
after doing several tests.

The row cache is caused by space allocation when several PX slaves are
inserting into several subpartitions, I noticed this after running two
insert append, the first had tons of row cache waits and the second insert

Looks like expected behaviour but in a 6 nodes RAC this look like a killer.



On Sat, Dec 19, 2009 at 7:01 PM, Greg Rahn <greg@xxxxxxxxxxxxxxxxxx> wrote:

> I dont recall the bug# but there is an issue related to quotas that
> can show when there are a relatively high number of concurrent PX
> sessions inserting into the same tablespace.  The work around is to do
> a direct grant (dba or unlimited quota sys priv is not sufficient).
> alter user <name> quota unlimited on <ts>;
> That may be enough for you to find the bug (look for the dc row cache
> stuff also).
> Hope that helps.
> On Fri, Dec 18, 2009 at 11:58 PM, LS Cheng <exriscer@xxxxxxxxx> wrote:
> >
> > The insert is simply insert append into... select, the degree of
> parallelism
> > is 8 for some tables, 4 for others and 2 for smaller tables. I can
> observe
> > that when there are 5 of these inserts running concurrently all of them
> > suffers high contention on row cache lock, specifically dc_object_ids and
> > dc_segments. Previously the load processes ran without parallel DML and
> > yesterday pdml was enabled. Same symptoms.
> --
> Regards,
> Greg Rahn

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