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Home -> Community -> Mailing Lists -> Oracle-L -> Re: Re: parallel index creation again:in which case, can we use p
Simply put, CPU is swifter than I/O (though not as much as some would have us believe!).
7-8 years ago, we benchmarked Oracle 7.1 PQ on single-processor IBM RS6000 nodes and found that the "sweet spot" was DOP=4 (where "DOP" means "degree of parallelism"). In testing on those 60Mhz PowerPC RISC processors, one CPU on 10000RPM SSA drives (using RAID1+0) would drive four PQ slave processes best. Adding more or removing any tended to reduce overall performance. One CPU can easily drive several PQ processes, because the bottleneck there is I/O...
I suspect that todays multi-Ghz processors, if supported by the right backplane, bus, and RAM, can do a little better... :-)
Steve,
I believe what you say, but it seems counter-intuitive.
If you only have one cpu, and you start two jobs, then it follows that the cpu needs to split itself to do the work.
So, what are we gaining? The CPU can only go so fast and do so much work.
Tom Mercadante
Oracle Certified Professional
-----Original Message-----
From: Stephen Evans [mailto:evans036_at_mc.duke.edu]
Sent: Thursday, February 13, 2003 9:39 AM
To: Multiple recipients of list ORACLE-L
Subject: RE: Re: parallel index creation again:in which case, can we use p
tom,
if the process is IO bound (ie consumes little cpu) then you can achieve a lot.
thanks,
steve
"Mercadante, Thomas F" <NDATFM_at_labor.state.ny.us>
Sent by: root_at_fatcity.com
02/12/2003 02:23 PM
Please respond to ORACLE-L
To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
cc:
Subject: RE: Re: parallel index creation again:in which case, can we use p
If you only have one CPU, then is parallel either not supported, or simply a waste of time?
I actually thought it was not supported. If you only have one CPU, what do you expect to gain?
Tom Mercadante
Oracle Certified Professional
-----Original Message-----
Sent: Wednesday, February 12, 2003 12:54 PM
To: Multiple recipients of list ORACLE-L
p
My experience shows that a parallel degree of less than 4 is nearly always slower than serial.
I would recommend tring parallel degree of 4.
-----Original Message-----
Sent: Wednesday, February 12, 2003 10:59 AM
To: Multiple recipients of list ORACLE-L
parallel with single cpu env?
Michael Ivanov,
Hi, Thanks for your reply.
In fact, I builded the index several times like, and the
result is persistent across difference test case:
So, I think buffer is not the cause of the parallel
execution slower. But I really do not get other parameter to tune:(
SQL> set term on timing on echo on feedback on SQL> alter session set sort_area_size = 100000000;
Session altered.
Elapsed: 00:00:00.01
SQL> create index idx_serial on viewcount( SID_LIST) nologging parallel
(degree 2) tablespace pqind;
Index created.
Elapsed: 00:18:01.36
SQL> drop index idx_serial;
Index dropped.
Elapsed: 00:00:00.16
SQL>
SQL> create index idx_serial on viewcount( SID_LIST) nologging tablespace
pqind;
Index created.
Elapsed: 00:06:48.04
SQL> drop index idx_serial;
Index dropped.
Elapsed: 00:00:00.06
SQL>
SQL> create index idx_serial on viewcount( SID_LIST) nologging parallel
(degree 2) tablespace pqind;
Index created.
Elapsed: 00:14:51.92
SQL> drop index idx_serial;
Index dropped.
Elapsed: 00:00:00.13
SQL>
SQL> create index idx_serial on viewcount( SID_LIST) nologging;
Index created.
Elapsed: 00:06:26.23
SQL> drop index idx_serial;
Index dropped.
Elapsed: 00:00:00.06
SQL>
SQL> create index idx_serial on viewcount( SID_LIST) nologging parallel
(degree 2) tablespace pqind;
Index created.
Elapsed: 00:14:44.58
SQL> drop index idx_serial;
Index dropped.
Elapsed: 00:00:00.13
SQL>
SQL> create index idx_serial on viewcount( SID_LIST) nologging tablespace
pqind;
Index created.
Elapsed: 00:06:49.09
SQL> drop index idx_serial;
Index dropped.
Elapsed: 00:00:00.07
SQL>
SQL> create index idx_serial on viewcount( SID_LIST) nologging parallel
(degree 2) tablespace pqind;
Index created.
Elapsed: 00:14:46.79
SQL> drop index idx_serial;
Index dropped.
Elapsed: 00:00:00.14
SQL>
SQL> create index idx_serial on viewcount( SID_LIST) nologging tablespace
pqind;
Index created.
Elapsed: 00:06:44.51
SQL> drop index idx_serial;
Index dropped.
Elapsed: 00:00:00.07
Regards
zhu chao
msn:chao_ping_at_163.com
www.happyit.net
www.cnoug.org(China Oracle User Group)
>Dear Chao.
>Did you try change order of index's creating- first noparallel, second with
parallel. I think you will look other results.
>
>> hi, dba friends:
>> some paper said, pqo should only be used in SMP machines, while
others
>> say, We can also use pqo in uniprocessor machines in some case. I am
trying
>> to use parallel index creation in the following env:
>>
>> Dell 1650 with 3 scsi160 disks and 1 CPU and 2G memory.
>> Oracle 9.2
>> Table contains 22000000 records,1.2GB
>> Table tablespace contains 3 datafiles , 400M, 400M and 600M, on seperate
3
>> disks. Index tablespace contains 3 datafiles, 200M, 200M and 200M on
>> seperate 3 disks.
>>
>>
>> SQL> set term on timing on echo on feedback on
>> SQL> alter session set sort_area_size = 100000000;
>> Session altered.
>> Elapsed: 00:00:00.01
>> SQL> create index idx_serial on viewcount( SID_LIST) nologging parallel
>> (degree 2) tablespace pqind; Index created.
>> Elapsed: 00:18:01.36
>> SQL> drop index idx_serial;
>> Elapsed: 00:00:00.16
>> SQL> create index idx_serial on viewcount( SID_LIST) nologging
tablespace
>> pqind; Elapsed: 00:06:48.04
>> This machine is exclusived used my me and It seems that PQO is
rather
>> slower than single thread. So is it still possible to use PQO on single
>> processor machines? Please share your experience and idear.
>> Thanks.
>>
>> Wait event like:
>>
>> Top 5 Timed Events
>> ~~~~~~~~~~~~~~~~~~
>> Total Event Waits Time
(s)
>> Ela Time -------------------------------------------- ------------
>> ----------- -------- PX qref latch
>> 48,371 415 40.94 PX Deq: Execute Reply
>> 176 340 33.54 PX Deq Credit: send blkd
>> 47,704 248 24.47 control file parallel write
>> 112 5 .48 PX Deq Credit: need buffer
>> 1,835 4 .38
>> ------------------------------------------------------------- ^LWait
Events
>> for DB: ORA9 Instance: ora9 Snaps: 19 -20
>> -> s - second
>> -> cs - centisecond - 100th of a second
>> -> ms - millisecond - 1000th of a second
>>
>>
>--
>Best regards
>Michael Ivanov, TD "ERA"
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-- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Tim Gorman INET: Tim_at_SageLogix.com Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).Received on Thu Feb 13 2003 - 10:34:37 CST
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