Oracle-L: RE: Shutdown abort

From: <Ivan_Rivera_at_doh.state.fl.us>
Date: Thu, 08 Aug 2002 07:58:39 -0800
Message-ID: <F001.004AF14A.20020808075839@fatcity.com>

I've also just finished looking over this same stuff for a class I'm teaching and would like to add that in 8i after the rolling forward process and the database is opened, SMON does as you said and periodically will scan the rollback segments and roll transactions back.

Meanwhile if a server process on behalf of a user encounters a block that it needs and that block was in an uncommitted transaction prior to the instance crash, it is not SMON that rolls the transaction back but the process itself that rolls the transaction back.

But in 8i there's also has what's called On-Demand Parallel Rollback which means if the same scenario is happening (server process needs block that's in an inconsistent state) but the block needed was part of a large uncommitted transaction then what happens is that the server process will rollback only the block that it needs to perform it's transaction and hand over the rest of that long transaction to be rolled back to SMON and if that transaction has more than a 100 rollback blocks and fast_start_parallel_rollback is set, SMON will use recovery slave processes to aid in speeding up this large rollback.

I guess what I'm trying to say is that it really depends on how large the uncommitted transaction is whether it's the server process itself that rolls it back or whether it just rollback the block it needs and then hands over the rollback job to SMON. Not trying to be picky over details just trying to add to the convo :). HTH. Ivan

-----Original Message-----
Sent: Thursday, August 08, 2002 10:48 AM To: Multiple recipients of list ORACLE-L

Stefan

Well, I finally found a good reason for studying for OCP! I would not have known this answer without being forced to study.

It depends on your Oracle version. The Oracle 8i answer is: On startup, Oracle performs recovery, including rolling forward all transactions. Oracle then opens the database for production use. In the background, SMON continues to roll back transactions that were not committed when the database shut down. If a process needs a block that was involved in an uncommitted transaction, then SMON goes ahead and rolls back that transaction so the process doesn't have to wait.

Dennis Williams
DBA
Lifetouch, Inc.
dwilliams_at_lifetouch.com

-----Original Message-----
Sent: Thursday, August 08, 2002 7:58 AM
To: Multiple recipients of list ORACLE-L

Hi list

stupid one: In case of a shutdown abort and startup, are the rollback activities discontinued after startup and the rollback segs are available again ? or not ?

regards,
Stefan

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Author: Stefan Jahnke
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