Slow running Delete query for same data volume
Date: Thu, 1 Apr 2021 16:27:35 +0530
Message-ID: <CAEjw_fgU-ort0a65NspX+h3nucpRH4NxG+5a9JEGYgGaCwMXBg_at_mail.gmail.com>
Hello all, We are using version 12.1.0.2.0 of Oracle exadata X3 machine. Seeing variable performance for a DELETE query even though the plan is the same. Though the number of rows are closely the same, we are seeing the runtime is increasing from ~15minutes to ~30minutes. As its version 12C, so I am able to fetch the sql monitor from these past two executions as attached here. But i am not seeing any information in the activity detail section of the report.
However I fetched the activity data from dba_hist_active_sess_history and it says the "cell multiblock physical read" is quite high for the slow execution. And also the objectid is pointing to the table partition which means it was also not on UNDO. So does it mean that we must be suffering from overall system slowness which impacted this query because of slow overall response time for "cell multiblock physical read" in database level?
DELETE /*+ full(TAB1) */ FROM TAB1 TAB1 WHERE ETC = 'XX' AND ID = 3 AND OTCD = 'YY' AND PART_DT = :B1 Select event, current_obj#, count(*) from dba_hist_active_sess_history group by event, current_obj# order by count(*) desc;
*For faster run :-*
EVENT CURRENT_OBJ# COUNT(*) cell multiblock physical read TAB1 73
TAB1 5 gcs drm freeze in enter server mode TAB1 1
*For slower run:-*
EVENT CURRENT_OBJ# COUNT(*)
cell multiblock physical read TAB1 170TAB1 14
-- http://www.freelists.org/webpage/oracle-lReceived on Thu Apr 01 2021 - 12:57:35 CEST
- text/plain attachment: Sql_monitor_list__1_.txt