3-node RAC 12.2 database on Centos7
We have an application which makes use of SQLAlchemy that is suffering
mightily from "cursor: pin S wait on X" executing the following SQL:
SELECT col.column_name, col.data_type, col.char_length,
col.data_precision, col.data_scale, col.nullable,
col.data_default, com.comments
FROM all_tab_columns col
LEFT JOIN all_col_comments com
ON col.table_name = com.table_name
AND col.column_name = com.column_name
AND col.owner = com.owner
WHERE col.table_name = :table_name
AND col.owner = :owner ORDER BY col.column_id
The application will launch ~200 concurrent sessions on startup. There is a
long initial period where many of them are waiting on the event then things
start clearing up and processing proceeds as expected. There are several
different plan hash values for the SQL, one of which didn't seem to suffer
from the issue so I created a sql baseline and crossed my fingers. I've
collected dictionary statistics as well but that made no difference.
While I do my own searching, does any one have any suggestions on how to
remove the delays?
Here is some ASH data showing the issue:
SQL> @ashtop sql_id,event "sql_id='0rz9dn5v75czn'" "TIMESTAMP'2018-06-28
18:45:00'" "TIMESTAMP'2018-06-29 00:00:00'"
Total
Seconds AAS %This SQL_ID EVENT
FIRST_SEEN LAST_SEEN DIST_SQLEXEC_SEEN
--------- ------- ------- -------------
---------------------------------------- -------------------
------------------- -----------------
75469 4.0 84% | 0rz9dn5v75czn cursor: pin S wait on X
2018-06-28 20:11:34 2018-06-28 20:38:54 1
6441 .3 7% | 0rz9dn5v75czn library cache lock
2018-06-28 20:11:41 2018-06-28 20:38:36 1
6243 .3 7% | 0rz9dn5v75czn kksfbc child completion
2018-06-28 20:11:44 2018-06-28 20:38:43 1
1592 .1 2% | 0rz9dn5v75czn
2018-06-28 20:11:34 2018-06-28 20:38:55 105
182 .0 0% | 0rz9dn5v75czn cursor: pin S
2018-06-28 20:12:34 2018-06-28 20:38:34 1
133 .0 0% | 0rz9dn5v75czn library cache: mutex X
2018-06-28 20:12:09 2018-06-28 20:38:32 1
18 .0 0% | 0rz9dn5v75czn enq: PS - contention
2018-06-28 20:13:17 2018-06-28 20:38:55 18
15 .0 0% | 0rz9dn5v75czn cursor: pin X
2018-06-28 20:13:41 2018-06-28 20:38:36 1
select snap_id, end_interval_time
8 .0 0% | 0rz9dn5v75czn PGA memory operation
2018-06-28 20:15:24 2018-06-28 20:38:44 1
2 .0 0% | 0rz9dn5v75czn PX Deq: Join ACK
2018-06-28 20:13:26 2018-06-28 20:32:12 2
1 .0 0% | 0rz9dn5v75czn row cache read
2018-06-28 20:35:18 2018-06-28 20:35:18 1
11 rows selected.
SQL> @ashtop session_id,sql_id,event "sql_id='0rz9dn5v75czn'"
"TIMESTAMP'2018-06-28 18:45:00'" "TIMESTAMP'2018-06-29 00:00:00'"
Total
Seconds AAS %This SESSION_ID SQL_ID EVENT
FIRST_SEEN LAST_SEEN DIST_SQLEXEC_SEEN
--------- ------- ------- ---------- -------------
---------------------------------------- -------------------
------------------- -----------------
934 .0 1% | 2065 0rz9dn5v75czn cursor: pin S wait on X
2018-06-28 20:11:34 2018-06-28 20:37:03 1
925 .0 1% | 1459 0rz9dn5v75czn cursor: pin S wait on X
2018-06-28 20:11:34 2018-06-28 20:35:26 1
917 .0 1% | 613 0rz9dn5v75czn cursor: pin S wait on X
2018-06-28 20:13:26 2018-06-28 20:38:53 1
893 .0 1% | 4360 0rz9dn5v75czn cursor: pin S wait on X
2018-06-28 20:11:34 2018-06-28 20:38:45 1
873 .0 1% | 973 0rz9dn5v75czn cursor: pin S wait on X
2018-06-28 20:11:44 2018-06-28 20:38:26 1
861 .0 1% | 3276 0rz9dn5v75czn cursor: pin S wait on X
2018-06-28 20:11:44 2018-06-28 20:38:44 1
854 .0 1% | 3877 0rz9dn5v75czn cursor: pin S wait on X
2018-06-28 20:11:34 2018-06-28 20:38:52 1
828 .0 1% | 4602 0rz9dn5v75czn cursor: pin S wait on X
2018-06-28 20:11:44 2018-06-28 20:38:50 1
827 .0 1% | 2547 0rz9dn5v75czn cursor: pin S wait on X
2018-06-28 20:11:34 2018-06-28 20:38:47 1
826 .0 1% | 491 0rz9dn5v75czn cursor: pin S wait on X
2018-06-28 20:11:44 2018-06-28 20:38:44 1
823 .0 1% | 251 0rz9dn5v75czn cursor: pin S wait on X
2018-06-28 20:15:06 2018-06-28 20:38:51 1
818 .0 1% | 2790 0rz9dn5v75czn cursor: pin S wait on X
2018-06-28 20:15:06 2018-06-28 20:38:35 1
798 .0 1% | 124 0rz9dn5v75czn cursor: pin S wait on X
2018-06-28 20:11:44 2018-06-28 20:32:06 1
761 .0 1% | 129 0rz9dn5v75czn cursor: pin S wait on X
2018-06-28 20:11:34 2018-06-28 20:38:45 1
745 .0 1% | 6 0rz9dn5v75czn cursor: pin S wait on X
2018-06-28 20:11:44 2018-06-28 20:38:51 1
734 .0 1% | 738 0rz9dn5v75czn cursor: pin S wait on X
2018-06-28 20:11:44 2018-06-28 20:37:01 1
731 .0 1% | 123 0rz9dn5v75czn cursor: pin S wait on X
2018-06-28 20:13:24 2018-06-28 20:38:37 1
730 .0 1% | 4117 0rz9dn5v75czn cursor: pin S wait on X
2018-06-28 20:11:34 2018-06-28 20:38:43 1
726 .0 1% | 1216 0rz9dn5v75czn cursor: pin S wait on X
2018-06-28 20:17:17 2018-06-28 20:38:52 1
710 .0 1% | 3 0rz9dn5v75czn cursor: pin S wait on X
2018-06-28 20:16:46 2018-06-28 20:36:23 1
20 rows selected.
SQL> select distinct(plan_hash_value) from dba_hist_sqlstat where sql_id =
'0rz9dn5v75czn' and snap_id >= 2378;
PLAN_HASH_VALUE
---------------
2901843923
1846450148
0
SQL> l
1 select plan_name, last_executed, enabled, accepted, fixed, executions
2 from dba_sql_plan_baselines
3* where sql_text like '%col.column_name, col.data_type, col.char_length%'
SQL> /
PLAN_NAME LAST_EXECUTED ENABLED ACCEPTED FIXED EXECUTIONS
---------------------------------------- -------------------- ----------
---------- ---------- ----------
SQL_PLAN_78xa0f27qf69ye98653aa YES YES YES 38562
Anyone have any ideas?
Thanks as always!