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Home -> Community -> Mailing Lists -> Oracle-L -> RE: Autoextend WAIT statistic?
I have heard from several sources that the v$ views are not as solid as they
should be. With all the emphasis on wait and event based tuning, they should
be more accurate. Has anyone done in-depth research on the collection
methods and accuracy of the x$ and v$ structures? Sounds like a project for
some of the gurus on the list... <HINT, HINT>
-----Original Message-----
Sent: Tuesday, November 26, 2002 8:25 PM
To: Multiple recipients of list ORACLE-L
As much as the v$"wait" views are touted they do have problems. First, I believe they are only updated every 3 seconds and can miss events. Second, examine enough samplings from the tables and you'll discover bizarre data. Events which managed to wait say 50 seconds in a single sampling period when the sampling rate was 5 Hz. On the other hand, one may see events which are continuous over many samplings, but their wait times are not incremented.
If you really want to know what's going on there's no substitute for a 10046 trace.
N.B., I am not stating the v$"wait" statistics tables are useless just that they have their shortcomings.
Ian MacGregor
Stanford Linear Accelerator Center
ian_at_SLAC.Stanford.edu
-----Original Message-----
Sent: Tuesday, November 26, 2002 3:26 PM
To: Multiple recipients of list ORACLE-L
Dennis,
I did some quick & dirty testing by creating a very small(10M) datafile with a large(2000m) autoextend clause. On the insert, the session was waiting on 'file open' for most of the time. When I did a rollback and reinserted the data, there were no waits (that I saw) on file open.
Interestingly, this wait event does not appear to be accurately tracked in v$session_event. In v$session_wait the seconds in wait (last trapped) was 132. In v$session_event, it shows 0. Okay, gurus, why? Am I missing something in this?
select * from v$session_wait where sid = 14
SID SEQ# EVENT
---------- ----------
P1TEXT P1P1RAW
P2TEXT P2P2RAW
P3TEXT P3 P3RAW WAIT_TIME SECONDS_IN_WAITSTATE
---------------------------------------------------------------- ----------
---------------- ---------- ---------------
14 322 file open
fib 4327126592
0000000101EAB640
iov 4327069760
0000000101E9D840
0 0
00 -1 132
WAITED SHORT TIME
select * from v$session_event where sid = 14
SID EVENT TOTAL_WAITS TOTAL_TIMEOUTS
TIME_WAITED AVERAGE_WAIT MAX_WAIT
Dan Fink
-----Original Message-----
Sent: Tuesday, November 26, 2002 2:30 PM
To: Multiple recipients of list ORACLE-L
Oracle says that when a file autoextends, there is a slight delay. Does anyone know which Oracle WAIT statistic that would appear under? We have been using autoextend on OLTP production tables for awhile now, and the results have been satisfactory. This is an ERP system, so the critical performance time is at month-end. Some of the developers are concerned that table autoextending may slow batch programs, and suggesting that I should determine which tables are likely to autoextend during month-end and add storage beforehand. I would like to ensure that I am fixing a real problem (short on time, like most of you), so I am wondering if autoextend was causing a delay, what wait statistic would it show up under. Any ideas?
Dennis Williams
DBA
Lifetouch, Inc.
dwilliams_at_lifetouch.com
-- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: DENNIS WILLIAMS INET: DWILLIAMS_at_LIFETOUCH.COM Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting servicesReceived on Wed Nov 27 2002 - 13:58:54 CST
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