You can read about it on OTN.
http://download-west.oracle.com/docs/cd/A87860_01/doc/index.htm
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When designing applications for Oracle Parallel Server, use sequence
numbers whenever possible. To maximize the use of sequences, each
instance's cache must be large enough to accommodate the sequences. The
default cache size holds 20 sequence numbers. To increase this, for example
to hold 200, use this syntax:
ALTER SEQUENCE SEQUENCE_NAME CACHE 200;
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If sequences are insufficiently cached or not cached at all, severe
performance problems may result with an increase in service times. This may
also result in reduced scalability.
If you experience performance problems, examine statistics in the
V$SYSTEM_EVENT view as described below to determine whether the problem is
due to the use of Oracle sequences:
A problem with sequences appears in V$SYSTEM_EVENT as extended average wait
times for "row cache locks" in the range of a few hundred milliseconds. The
proportion of time waited for row cache locks of the total time waited for
non-idle events will be very high.
For the DC_SEQUENCES parameter, the ratio of DLM_CONFLICTS to DLM_REQUESTS
will be very high. If this ratio exceeds 10 to 15% and the row cache lock
wait time is a significant portion of the total wait time, then it is
likely that the deterioration of service times is due to insufficiently
cached sequences.
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Kore Peterson
<[EMAIL PROTECTED]
u.ac.uk> To: CF-Talk <[EMAIL PROTECTED]>
cc:
12/15/2003 Subject: Oracle Sequences
06:43 AM
Please respond
to cf-talk
Anybody ever had problems with the request for a sequence timing out?
I thought the database would have just queued them up? Why would CF
keep hanging on them?
I've put a lock around the offending sequence to see if that solves it
but was wondering if there was any other possible problems out there?
This sequence is getting hit pretty heavily at the moment....
Cheers
--
-dc [ cf5, ora8.1.7, iis5 ]
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