Re: ORA-01555: snapshot too old: rollback segment number 24 with name "_SYSSMU24$" too small
- From: "Alex Gorbachev" <gorbyx@xxxxxxxxx>
- To: WITTENMYERJ@xxxxxxxx
- Date: Tue, 27 Jun 2006 22:11:41 +0200
My respect if you can have terrabyte OLTP system running stable with
auto gather stats job. Quite challenging. :)
If you have bug # - please share.
Stats gathering doesn't do "massive DML". What it does is a lot of
selects and assuming those are long running, one can expect it to fail
with ORA-1555 on a busy OLTP system. The only DMLs are done to
dictionary tables to update stats (unless I seriously missing
something). Invalidation of execution plans caused by updating
statistics should have far more noticeable impact I believe.
2006/6/27, Wittenmyer Joel - CO <WITTENMYERJ@xxxxxxxx>:
This sounds similar to a known bug with ASSM tablespaces. The stats job
updates tables in SYSAUX. Those tables have indexes and up to 10.2.0.2 if
an instance does massive DML (which the stats job does in our case.
Terabyte oltp with daily data loads and many schemas) on segments in an ASSM
tablespace that has indexes, the undo is unbelievable. In our case it
produces 10x the undo / redo it normally would. It can cause not only
ora-1555, but you can blow out the max extents (32767) for an undo segment.
The 'workaround' of coalescing the indexes prior to running such DML is only
minimally effective. The backport patch for previous versions in some cases
flat doesn't work (I know from experience.) The only sure fix is to upgrade
to 10.2.0.2, which I am told definitely fixes the issue, and which I am
preparing to do on several production instances even thought I HATE applying
the latest patchset (hornet's nest). Of course, if you are already on
10.2.0.2 and are seeing this, please let me know!
--
Best regards,
Alex Gorbachev
http://blog.oracloid.com
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