RE: sql_text during parsing
Date: Tue, 13 Jul 2021 16:00:46 +0000
Message-ID: <3ee6cc7d0c294bd5988d224d42945f9e_at_vontobel.com>
A small add-on to Jonathan’s perfect summary.
The following configuration will kill the monster if it comes again (credits to Sayan Malakshinov - my go-to place for Oracle diagnostic ☺ : https://twitter.com/dbms_xtender/status/1392499158368624641 ):
alter system set events 'trace [SQL_Compiler.*][sql: 99g4t6h9kfumw] {callstack: fname opiParse} controlc_signal()' ;
I’m not a mean person, but this SQL was generated by some convoluted Tableau workflow that shouldn’t run anymore (at least, they said so).
“Thanks”, I said, and then prepared for the worst.
Best regards,
Nenad
From: oracle-l-bounce_at_freelists.org <oracle-l-bounce_at_freelists.org> On Behalf Of Jonathan Lewis
Sent: Dienstag, 13. Juli 2021 13:41
To: ORACLE-L (oracle-l_at_freelists.org) <oracle-l_at_freelists.org>
Subject: Re: sql_text during parsing
Now that the heavy lifting has been done, I've got a couple of tweaks (which I've already mentioned on twitter) to echo here. In fact it's not going to make much difference to the trace in this example since the text is 70M, but you can reduce the content in the trace.
Looking at the error dump it appears that all we really need is a Session Cursor Dump as the SQL text from sql that is too long for the basic cursor dump format seems to be reported separately at the end of the dump; so change errorstack(2) to cursordump(1).
We trigger the dump on a call to opiparse - but in the test we parse a pl/sql package, we do some recursive SQL parsing, and so on - so opt parse is called a few times when we don't want it to be called; since we know the SQL_ID of the sql we're interested in, limit trace to just that SQL_ID with [SQLxxxxxxxxxxxxx].
Just in case the SQL is called (and has to be parsed) several times in the lifetime of a session, and doesn't end up in the cursor or pl/sql cache avoiding opiparse) let's make sure that we only dump the trace once using the {occurences: ....} option.
So the final thing I tried, based on Sayan's original test looked like this:
alter session set events 'trace [SQL_Compiler][SQL:69153ssxd3180]{callstack: fname opiParse} {occurence: end_after 1} disk=low cursordump(1)';
YMMV, but in a re-run of the tests for this note, the trace file dropped from 5MB to 500KB
Regards
Jonathan Lewis
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