Anjo has convinced me that I was indeed barking up the wrong tree (and
even if I was the tree didn't care)

He lead me into tests that shows my problem exhibits exactly the same
characteristics of trying to insert the same value into a unique index
simultaneously.  That somehow, one user does an insert with one value,
and before he commits, another session (usually different user -- not
always) tries to insert the same value.

Previously I had examined the developers code and convinced myself
that this could not be the case as he selects a sequence nextval into
a variable, then immediately uses that variable to create a the value
list for the insert.

I haven't found anything that makes me want to mistrust a sequence
nextval. (If anyone knows of one in 8.0.5 on Solars 2.7 please let me
know.) So I've got to mistrust something going on in the developers VB
based COM object running under MTX serving up ASP pages for IIS.
(Notice the long string of MS products there and you can guess how
that influences my suspicions.)

Since I've come to this realization, the event has not recurred, so I
don't have any statistics.  But we do know that when it starts, we see
incidents from all 8 webservers simultaneously.  Past evidence
collected for a blocker and a blocked session shows that they were on
the same webserver, but that's just 1 data point and we don't have any
other to confirm or deny that relationship.  Also when it starts, it
happens at a furious rate, dozens of sessions at once.  Then it
suddenly stops.  Curiously, the same applications on the same
webservers are handling 30 other databases which experience no
problems.   This points me back to the database.  <sigh>

One of the things I would like to do, is to record what the database
thought it answered for the select of the sequence nextval, and have
that for comparison when the application tries to do its insert.  My
dream would be to have a trace/log/journal/something that recorded the
nextval returned,user,session,serial#,and sysdate for every time the
sequence was read.  This would allow me to see discrepancies in the
select/insert and sessions that were trying to insert without actually
making the select.

Has anyone tried this level of tracing/logging before?

-rje


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Author: Robert Eskridge
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