RE: Interpreting USED_UREC from V$TRANSACTION - MOS response
Date: Tue, 10 Jul 2012 20:04:04 +0000
Message-ID: <BD475CE0B3EE894DA0CAB36CE2F7DEB4CE812D31_at_CWYIGMBCRP02.Corp.Acxiom.net>
Oracle has come back with:
"From what I got from the ARE team the information seems to be a bug that would need to be filed. The only thing is we would have to be able to duplicated so that we can get information to development. Not saying that we can not file a bug but we would have to obtain tracing at the time of the problem. If you can provide that then development would be able to fix it for all versions onward."
I guess I won't know exactly what happened until I get another ridiculous situation where a rollback covers billions of undo records. At least my monitor script now includes undo blocks! Thanks for all the responses!
DAVID HERRING
DBA
Acxiom Corporation
EML dave.herring_at_acxiom.com TEL 630.944.4762 MBL 630.430.5988
1501 Opus Pl, Downers Grove, IL 60515, USA WWW.ACXIOM.COM -----Original Message-----
From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Herring Dave - dherri Sent: Friday, July 06, 2012 12:20 PM
To: Oracle-L (oracle-l_at_freelists.org) Subject: Interpreting USED_UREC from V$TRANSACTION
Folks,
I'm monitoring a VERY large rollback operation and could use some help in understanding conflicting values for USED_UREC in V$TRANSACTION.
This is for 11.2.0.3 on RHEL 5.6. The transaction was a DROP COLUMN against a 1.3 TB table which I believe ran out of undo after 50+ hrs. The SQL was generated from a data modeling tool and even after warning about runtimes they wanted the command run exactly as generated.
Now that the DROP COLUMN command has been rolling back for 5 days, I'm getting pretty confused on what V$TRANSACTION is telling me, specifically USED_UREC. Periodically over the last few days I've been querying this view and the values decreased way below zero and are now back about 800 million. In all cases each check a little later showed the values were decreasing so I knew it was still rolling back:
Snapshot Date USED_UREC 02-JUL-12 10:32:12 390,963,088 03-JUL-12 18:41:54 -903,130,274 06-JUL-12 12:57:17 784,607,392
As the value for USED_UREC decreased near 0 I figured that'd be it, but then it seemed to go indefinitely below 0, then some point in the past 24 hrs. the value was reset about 800 million. Like I said, repeated checks so the value to be decreasing and also a DECODE(BITAND(t.flag,128), 0, NULL, 'Rollback') returns "Rollback".
So how can the value go negative and then jump back to 800 million? I'm pretty sure it didn't "wrap" and transactions can't span undo segments. This also makes it VERY difficult to figure out how long this will take.
The best I've come up with is comparing "redo entries" stat from AWR before the rollback with "rollback changes - undo records" stat in AWR during this rollback process. Should they eventually be equal, assuming little to no other activity on the DB?
DAVID HERRING
DBA
Acxiom Corporation
EML dave.herring_at_acxiom.com<mailto:dave.herring_at_acxiom.com>
TEL 630.944.4762
MBL 630.430.5988
1501 Opus Pl, Downers Grove, IL 60515, USA WWW.ACXIOM.COM<http://WWW.ACXIOM.COM>
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