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 v$memory_resize_ops Tips

Oracle Database Tips by Donald BurlesonMarch 10, 2015

Question:  How does the v$memory_resize_ops view help me monitor the the RAM resizing in my database?

Answer:  When using Automatic Memory Management (AMM) or "alter system" commands to re-size the SGA pool sizes and PGA region, the v$memory_resize_ops show the last 800 RAM resizing operations, both SGA and PGA.

Beware!  Too many resize operations with AMM can hurt your performance.  Make sure to run the below scripts to see the dates and amount of resizing operations on all of your SGA pools and PGA.

The v$memory_resize_ops view is important when tracking AMM, because excessive resizing operations ca hurt database performance.  This happens when there is not enough RAM.

This v$memory_resize_ops is also related to the v$sga_resize_ops that shows the last 800 SGA RAM resizing operations.  For each resize it shows whether it was a SHRINK or GROWTH, and whether it was a IMMEDIATE, DEFERRED or MANUAL resize operation.  This query will show all AMM resize operations:

select
   *
from
   v$memory_resize_ops;

This important script will show all resize operations in AMM:

amm_resizes_detail.sql

set pages 999

col c1 heading "start|time"
col c2 heading "type"       format a20
col c3 heading "operation"  format a20


break on c1 skip 2

select distinct
   to_char(start_time,'DD-MON-YY hh24:mi') c1,
   parameter c2,
   oper_type c3
from

See code depot for full scripts
   v$memory_resize_ops
order by
   c1
;

Below we see the output, showing the AMM resize operations over time, and the periods when AMM is being stressed:

16-JAN-14 09:21 pga_aggregate_target SHRINK
                sga_target           GROW


16-JAN-14 09:32 db_cache_size        GROW
                db_cache_size        SHRINK
                pga_aggregate_target GROW
                sga_target           SHRINK


16-JAN-14 17:22 pga_aggregate_target SHRINK
                sga_target           GROW

Below we see periods where automatic memory resize operations were frequent, indicating that there was too little RAM allocated to the 11g memory_target parameter:

amm_resizes_per_day.sql

set pages 999

col c1 heading "start|time"
col c2 heading "nbr|resizes" format 9,999

break on c1 skip 1

select distinct
   to_char(start_time,'YYYY-MM-DD') c1,
   count(*) c2
from
   See code depot for full scripts

   v$memory_resize_ops
group by
   to_char(start_time,'YYYY-MM-DD')
order by
   to_char(start_time,'YYYY-MM-DD')
;

Here we see total number of resize operations per day, important for knowing when the database is undergoing RAM shortages with RAM threshing in AMM.
 
start          nbr
time       resizes
---------- -------
2014-01-09      48
2014-01-10      89
2014-01-11      27
2014-01-12      91
2014-01-13      52

   
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Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

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