RE: row cache lock contention parallel insert

From: Mark W. Farnham <>
Date: Wed, 23 Dec 2009 07:10:45 -0500
Message-ID: <>

So how much dynamic extension is going on? Is this the bug where when one thread needs to allocate an extent all the parallel inserters to the same object pile up and also add an extent?  

So, if you count the number of extents on all the objects getting inserted into at 00:04:59 of your 5 minute cycle (presuming the previous cycle finished without exhausting the time slice), and you do it again when the work for the 5 minute period is over, are we routinely talking about a lot of extents being added or not?  

When you say 10 application processes but with 64 slaves, is that 64 total or 640 total? What is your runqueue or the equivalent for whatever OS you're on?  

End of diagnostic data questions.  

Random suggestion leading question: What is driving the five minute window? Is this controlled such that a set of processes does not start on the five minute boundary if the previous set has not finished? What sort of input is being consumed by the insert jobs? Are the three tables the input or the destination. If input, are they new sets of input or rows added to previously processed data? Is there a way to stagger the starts productively?  


From: [] On Behalf Of LS Cheng
Sent: Wednesday, December 23, 2009 3:46 AM To: Greg Rahn
Cc:; Subject: Re: row cache lock contention parallel insert  


Thanks for the info

The workload is more or less every 5 minutes 10 data load processes kicks in, 3 of them needs to load around 12 million of rows each (going through ETL which are 3 tables per process), the rest from 300000 to 3 million.

All insert append with parallel dml and PQ for the SELECT ( Basically there is only 10 application processes but with 64 slaves running almost all the time. All ETL Tables has more or less 4000 to 5000 subpartitions

I noticed also compatible is set to instead of, might be some old bug? Probably because when I was doing test with a test database, also with compatible set to I managed to reproduce massive row cache contention, when I changed compatible to row cache requests reduced by a factor of 10. I will change compatible to after holidays because they dont allow anymore system changes until then



On Tue, Dec 22, 2009 at 4:30 PM, Greg Rahn <> wrote:

That query is used for the row cache read call back for SEG$ when the
segment entry is not available in the row cache.  Once the row cache
entry is available, all the reads should go through row cache rather
than from disk. It seems that something may be wrong with the row
cache layer.

Can you describe the workload?
What are the other top SQLs?

On Mon, Dec 21, 2009 at 3:47 PM, LS Cheng <> wrote:

> Yes there are many executions on this two query:
> 2ym6hhaq30r73 - around 11 millions executions per hour
> SELECT type#, blocks, extents, minexts, maxexts, extsize, extpct, user#,
> iniexts, NVL (lists, 65535), NVL (GROUPS, 65535), cachehint,
> NVL (spare1, 0), NVL (scanhint, 0)
> FROM seg$
> WHERE ts# = :1 AND file# = :2 AND block# = :3
-- Regards, Greg Rahn --
Received on Wed Dec 23 2009 - 06:10:45 CST

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