Lok P,
The 19.10 RU backports a parameter optimizer_real_time_statistics according
to this note (
https://blogs.oracle.com/optimizer/real-time-statistics-parameter ;) by
Nigel Bayliss, with the default value of FALSE so on your next upgrade it
seems likely that the feature will disable itself automatically - which
suggests it would be safe to disable it manually.
I don't have access to a 19.9, so I assume that it is currently a hidden
parameter but maybe it's more subtle than that.
There's also the problem that your query is reporting the use of real-time
statisics, but the collection of the statistics is from DML, so maybe you
have to find a way to disable the entire realtime statistics feature to
bypass your dictionary cache activity.
Regards
Jonathan Lewis
On Thu, 17 Jun 2021 at 06:10, Lok P <loknath.73@xxxxxxxxx> wrote:
Actually I am not sure if we can relate our issue to exactly the same one
which you pointed above. Our Db version is 19.9.0.0.0. In our case it is a
simple SELECT query ( SELECT /*+ FULL(P) +*/ * FROM P ) doing FTS on a
table (holding 700million rows) from multiple sessions(20+ sessions) and
were experiencing DC lock on 'dc_realtime_colst/tabst' and all the other
new session accessing same object 'P' were gets locked in parse
stage(cursor pin s wait on X) there after creating a big storm of
concurrency. Support is pointing to the below bug and suggesting the patch
to install to fix this bug.
32042352
<https://support.oracle.com/epmos/faces/PatchDetail?requestId=24138539&_afrLoop=252185249564103&patchId=32042352&_afrWindowMode=0&_adf.ctrl-state=168q4vx617_93#>
HIGH
ROW CACHE MUTEX WAITS ON 19.8 WITH HIGH CONCURRENCY
<https://support.oracle.com/epmos/faces/PatchDetail?requestId=24138539&_afrLoop=252185249564103&patchId=32042352&_afrWindowMode=0&_adf.ctrl-state=168q4vx617_93#>
I had one related question, as this all seems to be related to 'dynamic
statistics/stats on conventional DML option' as that is visible in the note
section in the SELECT query plan. So is it advisable to switch that off for
this sql/table someway without negatively impacting it anything?
On Wed, Jun 9, 2021 at 9:21 PM Dominic Brooks <dombrooks@xxxxxxxxxxx>
wrote:
Out of interest, but off on a tangent from original thread, I am also
hitting what seems to be some oddities around this dc_realtime_colst.
Trying to drop a 230GB partitioned table it’s taking hours with notable
waits on DLM cross inst call completion and notable row cache lock waits on
dc_realtime_colst (and dc_histogram_defs).
For my issue, investigation is pointing towards two notes which point at
same bug:
*Drop User Cascade Command Hang On "DLM cross inst call completion" (Doc
ID 2671064.1)*
*Bug 31208287 - Deleting Enqueues For A Large Partitioned Table Hangs In
KJCI_WAIT/KJCI_PROCESSCRQ (Doc ID 31208287.8)*
WORKAROUND:
Drop in smaller portions. For instance first remove stats/histograms from
the
columns.
Sent from Mail <https://go.microsoft.com/fwlink/?LinkId=550986> for
Windows 10
*From: *Noveljic Nenad <nenad.noveljic@xxxxxxxxxxxx>
*Sent: *28 May 2021 08:57
*To: *Lok P <loknath.73@xxxxxxxxx>
*Cc: *ORACLE-L (oracle-l@xxxxxxxxxxxxx) <oracle-l@xxxxxxxxxxxxx>
*Subject: *RE: Locking issue
Yes, this bug should be fixed in 19.9 in the base release. I can tell
from my installation that it’s definitely fixed in 19.9.0.0.201020.
You can verify it for your patch level:
$ORACLE_HOME/OPatch/opatch lsinventory | grep 31414023
We still don’t know the reason for row cache lock id=62/63 allocations.
Unfortunately, the 10222 trace doesn’t spool the call stacks for cid=62/63,
only for cid=16/8.
We’d need to capture the call stacks for 62 or 63 to find out more.
If you want to go down that rabbit hole, I can prepare a DTrace script if
you’re on Solaris or gdb if you’re on Linux. The later would be better to
run on a test system if you’re unexperienced with gdb.
Let me know.
Best regards,
Nenad
*From:* Lok P <loknath.73@xxxxxxxxx>
*Sent:* Freitag, 28. Mai 2021 06:05
*To:* Noveljic Nenad <nenad.noveljic@xxxxxxxxxxxx>
*Cc:* ORACLE-L (oracle-l@xxxxxxxxxxxxx) <oracle-l@xxxxxxxxxxxxx>
*Subject:* Re: Locking issue
Thank you Nenad. We have oracle version 19.9.0.0. Need to check patch
details. But it seems from the bug details , this bug should have been
fixed by this version. correct me if wrong.
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