Good question – sorry for missing that out.
11.2.0.4
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From: Stefan Knecht <knecht.stefan@xxxxxxxxx>
Sent: Tuesday, April 17, 2018 9:54:57 AM
To: Dominic Brooks; oracle-l-freelists
Subject: Re: Crazy dynamic sampling?
Are you on 12.1.0.2 ?
On Tue, Apr 17, 2018 at 3:49 PM, Dominic Brooks
<dombrooks@xxxxxxxxxxx<mailto:dombrooks@xxxxxxxxxxx>> wrote:
In addition to invisible indexes not being so invisible, I hash partitioned
some global PK indexes to reduce insert hot block contention.
These two things – invisible local indexes with some unusable subpartitions and
hash partitioned PK indexes - are the only things which changed.
I’ve now got a few handfuls of statements which, in addition to some of them
doing table expansion thanks to the not-so-invisible invisible indexes, are
doing crazy long hard parsing – like 30 to 40 minutes. And that causes knock-on
effects to other sessions in the same workflow for the same sql / objects with
“cursor: pin S wait on X” and “library cache lock”
The likely culprit is dynamic sampling. I can see the sessions doing lots of IO
against different table partitions as part of the hard parse.
Otherwise the health of the database is no less healthy than it was before and
the SQL is the same SQL as it was before.
Whilst I wait for an optimizer trace file and some other dumps/traces, any wild
theories as to why just hash partitioning a global PK might cause this?
________________________________
From: Dominic Brooks <dombrooks@xxxxxxxxxxx<mailto:dombrooks@xxxxxxxxxxx>>
Sent: Tuesday, April 10, 2018 11:09:03 AM
To: oracle-l@xxxxxxxxxxxxx<mailto:oracle-l@xxxxxxxxxxxxx>
Subject: Re: Invisible indexes and table expansion
Probably just covered by bug 16544878.
Sent from my iPhone
On 10 Apr 2018, at 10:50, Dominic Brooks
<dombrooks@xxxxxxxxxxx<mailto:dombrooks@xxxxxxxxxxx>> wrote:
Just working through a problem, gathering evidence and trying to reproduce.
And it’s difficult for me to get an optimiser trace file in the environment.
In an 11.2.0.4 environment, I’ve got a whole bunch of queries now using table
expansion - VW_TE_2.
Recent change was to add three local indexes, each with a subset of
partitions as usable - something which table expansion was designed to help
with.
But they are invisible indexes.
So my theory is the invisibility is limited - ie they are visible enough to
cause table expansion - but then can’t be used.
Anyone looked into something similar?
Cheers
Dominic
Sent from my iPhone
