First generate a hypothesis:
H1: Oracle has developed an algorithm that tries to identify garbage that
should never have been sent to the database and puts it at the top of list for
getting chucked out of the SGA at the earliest possible moment to minimise the
threat of memory fragmentation.
Devise a test that will prove the hypothesis wrong: Left as exercise.
Maybe there's some memory related detail that pushes things to the flush end of
the LRU - viz: a statement that uses less than X Bytes in the libnrary cache is
a fragmentation threat and likely to be garbage (and cheap to recreate if it
wasn't).
What happens if the query is : select 1 from single-row-table where pk =
constant;
----
More seriously - how much "like" the example are the statement that are
evicted; what does the most complex one you can identify look like ?
Regards
Jonathan Lewis
________________________________________
From: oracle-l-bounce@xxxxxxxxxxxxx <oracle-l-bounce@xxxxxxxxxxxxx> on behalf
of Noveljic Nenad <nenad.noveljic@xxxxxxxxxxxx>
Sent: 03 March 2020 14:52
To: ORACLE-L (oracle-l@xxxxxxxxxxxxx)
Subject: shared pool evictions
The SQL statements like the one below are getting evicted from the shared pool
within a couple of minutes on a 18c database:
select /* nenad */ 1 from dual ;
The parameters are set as follows:
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
sga_target big integer 10G
shared_pool_size big integer 0
The size of the shared pool is ~1.6 GB:
select name,bytes/1024/1024/1024 gb from v$sgainfo ;
NAME GB
Shared Pool Size 1.6875
There weren't any recent resize operations.
All statements are taking around 25% shared pool space in total:
select ( sum(sharable_mem)+sum(persistent_mem)+sum(runtime_mem) )/1024/1024 mb
from v$sql ;
478.27296257019
Since there are some statements residing a little bit longer in the shared
pool, for which there aren't any open cursors, we can exclude "alter system
flush shared_pool" being the source of the problem, I think.
Any ideas how to approach this systematically?
Thanks,
Nenad
https://nenadnoveljic.com/blog/
____________________________________________________
Please consider the environment before printing this e-mail.
Bitte denken Sie an die Umwelt, bevor Sie dieses E-Mail drucken.
Important Notice
This message is intended only for the individual named. It may contain
confidential or privileged information. If you are not the named addressee you
should in particular not disseminate, distribute, modify or copy this e-mail.
Please notify the sender immediately by e-mail, if you have received this
message by mistake and delete it from your system.
Without prejudice to any contractual agreements between you and us which shall
prevail in any case, we take it as your authorization to correspond with you by
e-mail if you send us messages by e-mail. However, we reserve the right not to
execute orders and instructions transmitted by e-mail at any time and without
further explanation.
E-mail transmission may not be secure or error-free as information could be
intercepted, corrupted, lost, destroyed, arrive late or incomplete. Also
processing of incoming e-mails cannot be guaranteed. All liability of Vontobel
Holding Ltd. and any of its affiliates (hereinafter collectively referred to as
"Vontobel Group") for any damages resulting from e-mail use is excluded. You
are advised that urgent and time sensitive messages should not be sent by
e-mail and if verification is required please request a printed version.
Please note that all e-mail communications to and from the Vontobel Group are
subject to electronic storage and review by Vontobel Group. Unless stated to
the contrary and without prejudice to any contractual agreements between you
and Vontobel Group which shall prevail in any case, e-mail-communication is for
informational purposes only and is not intended as an offer or solicitation for
the purchase or sale of any financial instrument or as an official confirmation
of any transaction.
The legal basis for the processing of your personal data is the legitimate
interest to develop a commercial relationship with you, as well as your consent
to forward you commercial communications. You can exercise, at any time and
under the terms established under current regulation, your rights. If you
prefer not to receive any further communications, please contact your client
relationship manager if you are a client of Vontobel Group or notify the
sender. Please note for an exact reference to the affected group entity the
corporate e-mail signature. For further information about data privacy at
Vontobel Group please consult www.vontobel.com<https://www.vontobel.com>.
--
//www.freelists.org/webpage/oracle-l
