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Home -> Community -> Mailing Lists -> Oracle-L -> Re: Deadlock Interpretation Assistance Requested
Hi
In my opinion, this is an ITL issue. When a process need an ITL and have to wait for it , then it pseudo randomly selects a locked row (from that block) and enqueues itself in to the waiters queue. But the row_waited information in v$session will be null. In rare cases, it is possible for the deadlock to occur if the ITL waiter holds the row that is needed by the other process.
I would ask, what is the frequency of this deadlock ? Is this the first occurrence ? If it is the first occurrence, then I would wait for the next occurrence and then spend time and resource.
Hope this helps!!
Thanks
Riyaj "Re-yas" Shamsudeen
Certified Oracle DBA
"These are my opinions and does not bind my employer. Use at your risk"
elkinsl_at_flash
.net To: Multiple recipients of list ORACLE-L
<ORACLE-L_at_fatcity.com>
Sent by: cc:
root_at_fatcity. Subject: Deadlock Interpretation
Assistance Requested
com
02/10/01
07:00 PM
Please
respond to
ORACLE-L
Listers,
HP-UX 11.0, V7.3.4.3. Deadlock trace file snippet:
SELECT * FROM UNIT_STATISTICS WHERE UNIT_ID = :b1 AND MONTH = :b2 AND
YEAR = :b3 AND RANK_CODE = :b4 FOR UPDATE OF QUANTITY
<snip>
Deadlock graph:
---------Blocker(s)-------- ---------Waiter(s)
--- Resource Name process session holds waits process session holds waits TX-00180008-000042d6 837 635 X 784 481 S TX-00160010-00004412 784 481 X 837 635 X Rows waited on: Session 481: no row Session 635: obj - rowid = 00000722 - 00000289.0033.0102 I've never really encountered all that many deadlocks before. The ones I *have* seen in the past were the "classic" TX locks where user A has a row locked that user B needs and vice versa and the mode requested was X. On Friday, the DBA's sent me a trace file from a deadlock (with the info above from that trace file) and asked me to investigate. The deadlocks they had seen in the past were due to application coding issues, hence their tossing this to the development side of the house. After a lot of research on Metalink, the Steve Adams siteReceived on Sun Feb 11 2001 - 22:50:33 CST
(http://www.ixora.com.au), and Usenet archive searches (www.deja.com), the
S mode wait for session 481 (and no row) makes me think this isn't the typical application induced deadlock due to the way and order in which locks are acquired. There are 3 foreign keys on the table, and, each of them are indexed. There is no bitmap index. PCT_FREE is 10 and PCT_USED is 40. I don't really know all that much about how heavily DML is issued against the table. But, after reading material on when the wait is in S mode, I wonder if this might be an ITL issue. From what I've read the past 2 days, there could be other reasons for the S mode wait, but, waits for Unique/PK enforcement, insufficient ITL slots, and bitmap index were the most common reasons mentioned. Because the statement reported was a SELECT FOR UPDATE, I've eliminated (correctly?) the check for uniqueness wait during inserts, and, with no bitmap index on the table, that leaves the ITL slots as the main candidate. What I need to do is determine if this is indeed an application coding issue, or, if I need to kick this back to the DBA's and let them research it. And I don't mean that in a finger pointing way. The DBA's and developers there work well together. From what I've read and learned so far, this deadlock doesn't seem to be an application coding issue. I am thinking about saying that and asking them (if they haven't already) to open a TAR and provide the trace file to Oracle Support. If anyone has any comments or suggestions, I would appreciate hearing them
(because if this could still be due to an application coding issue, more
research needs to be done on the development and/or my side of the house). Regards, Larry G. Elkins elkinsl_at_flash.net -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: INET: elkinsl_at_flash.net Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists -------------------------------------------------------------------- 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
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also send the HELP command for other information (like subscribing). -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: INET: Riyaj_Shamsudeen_at_i2.com Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists -------------------------------------------------------------------- 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
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