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Re: interpreting statspack reports ( PX Deq )

From: Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk>
Date: Fri, 14 Jun 2002 08:28:31 +0100
Message-ID: <1024039764.16314.0.nnrp-10.9e984b29@news.demon.co.uk>

The "PX Deq Credit: send blkd" is not necessarily an idle event, and can be indicative of a sub-optimal parallel execution plan.

The significance of "Send Blkd" is that the process has some information to forward and it is being blocked. If this occurs in the "parallel to serial" stage of a "QC (range)" transfer, then it is an idle event, and the processes that are waiting their turn will be ticking over on this event every 2 seconds. If it is in a "parallel to parallel" phase, then each block is a time-wasting block, will affect total throughput time, and probably incurs the overhead of an o/s task switch.

--
Jonathan Lewis
http://www.jlcomp.demon.co.uk

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Ricky Sanchez wrote in message <3D09555E.2303AF3C_at_more.net>...

>Indeed these are parallel query events. With respect to the database
>they can be ignored as "idle events". If parallel query is a performance
>issue for you, approach it as a sql tuning exercise instead of a
>database tuning issue.
>
>Statspack has a table you can modify to filter these out. Log in as
>perstat or whoever owns the statspack schema and list the tables. One of
>them has the word "idle" in it and will be the table to change. Look at
>the rows and insert the text of the events - precisely, as it is case
>sensitive.
>
>The only way to fully comprehend the events reported in statspack is to
>thoroughly understand the database itself. The best doc for that purpose
>is still the concepts manual.
>
>- ricky
>
>
>john wrote:
>>
>> Oracle 8i ( 8.1.7.0.0 )
>> Solaris 8
>> __NO__ Parallel Server but am using Parallel Query
>>
>> I have at the top 5 of the wait events the following:
>>
>> Top 5 Wait Events
>> ~~~~~~~~~~~~~~~~~ Wait
>> % Total
>> Event Waits Time (cs)
>> Wt Time
>> -------------------------------------------- ------------ ------------
>> -------
>> PX Deq Credit: send blkd 334,105 176,389
>> 37.10
>> PX Deq: Execution Msg 35,860 57,729
>> 12.14
>> PX Deq: Table Q Normal 865,976 50,065
>> 10.53
>> PX Deq: Execute Reply 22,596 46,401
>> 9.76
>> db file scattered read 285,813 44,901
>> 9.44
>> -------------------------------------------------------------
>>
Received on Fri Jun 14 2002 - 02:28:31 CDT

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