Why don‘t you trace the process?
Von meinem iPhone gesendet
Am 23.06.2022 um 15:40 schrieb Pap <oracle.developer35@xxxxxxxxx>:
Thank you Lothar. Actually all the indexes on this mon partitioned table are
btree indexes. And also I checked DBA_OPTSTAT_OPERATION_TASKS in which there
is breakup of howmuch time each index stats gather took. And it says those
all indexes are combined finishing in minutes.
On Thu, 23 Jun 2022, 6:40 pm l.flatz@xxxxxxxxxx, <l.flatz@xxxxxxxxxx> wrote:
Hi,
there was a change in the way bitmap index stats are calculated.
Check out Doc ID 2611336.1
Thanks
Lothar
----Ursprüngliche Nachricht----
Von : oracle.developer35@xxxxxxxxx
Datum : 23/06/2022 - 14:10 (MS)
An : mohamed.houri@xxxxxxxxx
Cc : oracle-l@xxxxxxxxxxxxx
Betreff : Re: Stats gather taking longer -19c
Thank you Mohamed.
So basically we must have to remove the hard coded sample and use to auto
sample size in all the places. Without this the histogram would be old types
and also distinct value calculation would be old types.
However we are trying to understand, why it's taking 30minutes more now in
19c even with same 50% sample , which was used in 11.2? Is it because any
bug here in 19c?
On Thu, 23 Jun 2022, 5:13 pm Mohamed Houri, < mohamed.houri@xxxxxxxxx>
wrote:
Pap,
Its having histograms on ~36 columns but all of them are still showing
height-balanced and frequency. I was expecting those to be hybrid , but its
didnt happen, may be because of the way the stats getting gathered on this
table i.e. with hard coded 50% sample i.e as below.
If you are in 12c and above and you still find histograms of the legacy
HEIGHT BALANCED type then it is either that
the statistics for the concerned tables have not yet been calculated in
the newer Oracle version
or that you are calculating the statistics with a non-default value of the
estimate_percent ( sampling percentage): default value being
AUTO_SAMPLE_SIZE
It looks like you are in the second situation since you are using 50% a
sample percentage that you should never have done; since the
AUTO_SAMPLE_SIZE default value governs,among others, the approximate_ndv
algorithm and the new histogram types
Best regards
Mohamed Houri
Le jeu. 23 juin 2022 à 12:23, Pap < oracle.developer35@xxxxxxxxx> a écrit :
Hi, We moved from 11.2.0.4 to version 19.11.0.0.0 of oracle for this
database. And we are seeing for one of the table the stats gather has been
taking longer. It was used to take ~5-6minutes vs now its taking
~30-40minutes. Dont have enough AWR history to verify the exact run time
from ASH/AWR. But we can see it from the application log which notes the
start and end time of the stats gather.
There does exists 5 indexes in this table but when i am seeing ,
DBA_OPTSTAT_OPERATION_TASKS its showing ~1 minutes for all the index stats
gather combinely. Its the table/column gather which takes longer.We are
not able to test it as we dont have a 11.2 lower environment with us now
though.
The table size is 25Gb and is non partitioned one holding ~13million rows.
Its having 111 columns. Its having histograms on ~36 columns but all of
them are still showing height-balanced and frequency. I was expecting
those to be hybrid , but its didnt happen, may be because of the way the
stats getting gathered on this table i.e. with hard coded 50% sample i.e
as below.
exec DBMS_STATS.GATHER_TABLE_STATS (OWNNAME => NULL, TABNAME =>
table_name, ESTIMATE_PERCENT => 50, CASCADE => TRUE, method_opt => 'FOR
ALL COLUMNS SIZE AUTO', DEGREE => 4);
So my question is what must be the reason that same stats gather with ~50%
sample size now taking ~30minutes more on 19C as compared to 11.2 where it
was finishing in ~5minutes?
--
Houri Mohamed
Oracle DBA-Developer-Performance & Tuning
Visit My - Blog
Let's Connect - Linkedin Profile
My Twitter - MohamedHouri
