LATCH FREE :space background task

LATCH FREE :space background task

Latch free is a memory related specifically shared pool event which occur due to lack of space for the session to hold a latch.

~~~~~~~~~~~~~~~~~~                                                   wait   Call
Event                                            Waits    Time (s)   (ms)   Time
----------------------------------------- ------------ ----------- ------ ------
CPU time                                                     3,914          47.2
latch free                                     234,621       2,162      9   26.1

In AWR report, the top latch with high sleep activity is space background task which is a background task which manage the latch space with the slaves.

Latch Activity  DB/Inst: DB9ZX/DB9  Snaps: 14242-14243
->"Get Requests", "Pct Get Miss" and "Avg Slps/Miss" are statistics for
  willing-to-wait latch get requests
->"NoWait Requests", "Pct NoWait Miss" are for no-wait latch get requests
->"Pct Misses" for both should be very close to 0.0

                                           Pct    Avg   Wait                 Pct
                              Get          Get   Slps   Time       NoWait NoWait
Latch                       Requests      Miss  /Miss    (s)     Requests   Miss
------------------------ -------------- ------ ------ ------ ------------ ------
space background task la         37,163   20.4    0.6      2        6,132    3.4

Top sleep breakdown related to this latch is also significant

Latch Sleep breakdown  DB/Inst: DB9ZX/DB9  Snaps: 14242-14243
-> ordered by misses desc
space background task latc          37,163        7,595       4,309       3,360

Latch Miss Sources  DB/Inst: DB9ZX/DB9 Snaps: 14242-14243
-> only latches with sleeps are shown
-> ordered by name, sleeps desc

                                                     NoWait              Waiter
Latch Name               Where                       Misses     Sleeps   Sleeps
------------------------ -------------------------- ------- ---------- --------
space background task la ktsj_grab_task                   0      2,603    4,239
space background task la ktsj_detach_task                 0      1,625       69
space background task la ktsj_smco_purgeexpired           0         75        0
space background task la ktsjCreateTask                   0          6        1


Please increase the parameter to cache the cursors for efficient parsing and also reduce the space background process slaves which spawn higher.
alter system set session_cached_cursors=150 scope=spfile;
alter system set "_max_spacebg_slaves"=64;

Note: Reboot is required to set the parameter.

Leave a Reply

%d bloggers like this: