RE: Causes of CF (Control file) Enqueues on Index Creation?
- From: David Aldridge <david@xxxxxxxxxxxxxxxxxx>
- To: T.Koppelaars@xxxxxxxxxxxxxxxxxxxx, Oracle List <oracle-l@xxxxxxxxxxxxx>
- Date: Wed, 12 Sep 2007 10:51:50 -0700 (PDT)
If the load were modified to be direct path, and I've no idea why it isn't
already to be honest, then my intuition tells me that would remove the
possibility of delayed block cleanout occuring ... does that sound correct? I
can't think why the blocks would need to be cleaned following direct path
insert.
"Koppelaars, Toon" <T.Koppelaars@xxxxxxxxxxxxxxxxxxxx> wrote: v\:*
{behavior:url(#default#VML);} o\:* {behavior:url(#default#VML);} w\:*
{behavior:url(#default#VML);} .shape {behavior:url(#default#VML);}
If delayed block cleanout causes writes to the controlfile, then this might
be your problem.
When the index is created then the blocks are reread from disk and at that
moment are cleaned out and all the parallel slaves are fighting for the CF
enqueue.
---------------------------------
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On
Behalf Of David Aldridge
Sent: woensdag 12 september 2007 14:32
To: Oracle List
Subject: Causes of CF (Control file) Enqueues on Index Creation?
We recently noticed, through Quest Performance Analysis, that a particular
index creation statement on a newly populated table occasionally suffers from
enqueue waits that extend the creation time from a few minutes to over an hour.
We used statspack to investigate further and found that at the time of
index creation we get a spike in CF enqueue waits.
I have read Anjo Kolk's whitepaper "Description of Oracle7 Wait Events and
Enqueues" http://www.akadia.com/download/documents/session_wait_events.pdf in
which he identifies an imposing list of situations in which the CF enqueue is
used.
The index is a locally partitioned single column uncompressed b-tree built
in parallel degree 8 against a range partitioned heap table with 8 partitions.
The table has just been loaded when this index is created and it's the first to
be created post-load. Other subsequently-built indexes do not appear to have
suffered from this problem. the index creation takes place in a new session
that starts immediately after a previous session has populated the table,
commited and gracefully exited. The issue occurs intermittently, not on every
occasion that the table is loaded.
I don't have access to the statspack data we extracted at the moment ...
I'll post it as soon as I do.
Does anyone have any quick thoughts about the relationship between creating
an index and a control file lock? I'm really pushing the limits of my internals
knowledge here -- OK, actually I have gone past it :(
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