Slightly askew, old advice memory triggered by JL's mention of pinned:
Survey what you chronically use, most especially things that you use
intermittently but which fall on the slope of the "worth it to keep in
memory to avoid the reload" and put them in your warm start procedure for
any instances serviced by listeners that use them (either primary and
secondary or everything, depending on your environment).
Consider strongly whether that means big stuff that is used infrequently as
well, and CONSIDER whether your entire applications pool of stored
procedures is a reasonable amount of memory to consume as pinned.
Your mileage MOST CERTAINLY WILL VARY, and there is a special place in hell
if it exists for anyone who suggests I suggested this as a best practice.
Within reason and in some very notable high throughput environments that I
am legally prohibited from documenting this can be a HUUGE savings and a
more stable environment. It *may* even be useful dovetailed with a planned
monthly or quarterly pair of restarts if some memory heavy stored procedures
only run on month, quarter, and year end.
Packing these things all in pinned so that everything that fluctuates and is
not pinned tends to be contiguous can be a big advantage this method may
implement. INCLUDE THE SYS AND SYSTEM STUFF that you use.
It is NOT that Oracle won't sort of do all this for you. But this remains
something a good operational DBA can do that would be very difficult for
Oracle (or anyone) to automate well for the general case. There are
definitely cases where the effort is worthwhile.
Good luck,
mwf
PS: This ancient advice is NOT obsolete due to Oracle's memory tradeoff
automation. In fact the balance point of it being worthwhile is tipped
toward more often being worthwhile as this thread underscores.
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx]
On Behalf Of Jonathan Lewis
Sent: Monday, February 04, 2019 5:16 AM
To: Martin Klier - Performing Databases GmbH
Cc: Oracle-L Freelists
Subject: Re: ASMM - resizing triggers/thresholds
Two possibilities -
a) as you suggest, a test is not made immediately after the flush shared
pool, with the result that the shared pool has started to fill by the time
the test is run and the reparsing that occurs persuades Oracle that a shrink
would be a bad idea.
or maybe
b) when you flush the shared_pool items that are pinned are not flushed, and
if you have a lot of pinned items scattered across the shared pool then you
may have some items in every granule so that granules can't be re-allocated.
(But I think in this case you might see "deferred" shrink/grow reported in
v$sga_resize_ops / v$memory_resize_ops. If the whole granule can't be
re-allocated you may still see buffer cache activity in the shared_pool
memory with v$sgastat showing memory with the name 'KGH: NO ACCESS'.
If you can flush the shared pool can't you follow up with a manual resize of
the db_cache_size ? As a test, if nothing more ?
Regards
Jonathan Lewis
________________________________________
From: Martin Klier - Performing Databases GmbH
<martin.klier@xxxxxxxxxxxxxxxxx>
Sent: 04 February 2019 08:59:08
To: Jonathan Lewis
Cc: Oracle-L Freelists
Subject: Re: ASMM - resizing triggers/thresholds
Hi Jonathan,
thank you for the ideas!
Maybe this mechanism is not triggered by flushing the shared pool. Do you
think that's possible?
Regards
--
Martin Klier // Performing Databases GmbH Managing Partner // Senior DB
Consultant Oracle ACE Director
martin.klier@xxxxxxxxxxxxxxxxx // https://www.performing-databases.com
________________________________
Von: "jonathan" <jonathan@xxxxxxxxxxxxxxxxxx>
An: "Oracle-L Freelists" <oracle-l@xxxxxxxxxxxxx>, "Martin Klier"
<martin.klier@xxxxxxxxxxxxxxxxx>
Gesendet: Samstag, 2. Februar 2019 15:03:43
Betreff: Re: ASMM - resizing triggers/thresholds Martin,
If you look for the hidden parameters like "%memory_broker%" that gives you
some clues.
12.2.0.1
NAME SES_VAL
--------------------------------------------- ------------------------------
_automemory_broker_interval 3
_memory_broker_log_stat_entries 5
_memory_broker_marginal_utility_bc 12
_memory_broker_marginal_utility_sp 7
_memory_broker_shrink_heaps 15
_memory_broker_shrink_java_heaps 900
_memory_broker_shrink_streams_pool 900
_memory_broker_shrink_timeout 60000000
_memory_broker_stat_interval 30
I believe MMAN handles the memory management - so you could enable wait
state tracing on that process in a sandbox.
I think there's a calculation every 3 seconds to determine whether or not
memory allocations should change, although strangely the parameters above
suggest both 3 seconds and 30 seconds . The former apparently is for AMM
while the latter is for ASMM.
The marginal_utility suggests to me that the calculation involves the shared
pool / buffer cache advice regarding time saved by changing memory size (a
variant of the details shown in the AWR), with a requirement (perhaps) of a
minimum improvement (12%, 7%) in performance before a change will be
triggered.
There is a parameter _memory_management_tracing, default 0, that might
enable tracing of the feature(s).
Regards
Jonathan Lewis
________________________________________
From: oracle-l-bounce@xxxxxxxxxxxxx <oracle-l-bounce@xxxxxxxxxxxxx> on
behalf of Martin Klier - Performing Databases GmbH
<martin.klier@xxxxxxxxxxxxxxxxx>
Sent: 31 January 2019 10:00:35
To: Oracle-L Freelists
Subject: ASMM - resizing triggers/thresholds
Hi listers,
how and when are memory areas like DB cache and shared pool being resized,
when the instance runs in Automatic Shared Memory Management?
In my case, I have a system that has had some shared pool eating (child
cursor issue, blowing up the library cache), which was resolved. Now we have
a de-facto undersized buffer cache and low library cache consumption, but I
can't see any resizing taking place. I have SGA max size = SGA Target and no
minimum values for any component here.
Platform: Linux, Oracle EE 12.2.0.1
It would not be a big problem to restart the instance at some point, but
this may be different for other cases. So my interest is more educational.
:) In short: Where are the thresholds, what does trigger the resizing, how
often is it scanned, when does it happen?
Thanks in advance!
--
Martin Klier // Performing Databases GmbH Managing Partner // Senior DB
Consultant Oracle ACE Director
martin.klier@xxxxxxxxxxxxxxxxx // https://www.performing-databases.com
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