indeed hard parse in this case is better than waiting eternity due to
oracle bugs.
-----Original-Nachricht-----
Betreff: Re: shared pool waits
Datum: 2021-09-21T09:11:20+0200
Von: "Pap" <oracle.developer35@xxxxxxxxx>
An: "ahmed.fikri@xxxxxxxxxxx" <ahmed.fikri@xxxxxxxxxxx>
Not getting it fully though. If we purge a sql from cursor cache, doesn't
it mean there will be hard parsing and that will cause more contention and
take more CPU to parse subsequently? Though I am also trying to understand
Lok's point, as we should have noticed the in_hard_parse flag as 'Y' in
case this issue would have been caused by hard parse.
But again , when I see the P1 and P1text while the ASH shows the event as
'library cache:mutex x' or 'cursor mutex s', they are pointing to the same
sql_text only. Does that mean even doing soft parsing only but because of
the so many number of executions/soft parses we are suffering? But then I
am wondering why do we see these issues mainly while stats gathering is
running from another session on the same underlying object? How can this be
related?
The query looks like below.
SELECT MAX (ID1) FROM TAB1 WHERE C1= :B1 AND C2 = :B2
----------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost
(%CPU)| Time | Pstart| Pstop |
----------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | 4
(100)| | | |
| 1 | PARTITION RANGE SINGLE | | 1 | 52 |
| | KEY | KEY |
| 2 | SORT AGGREGATE | | 1 | 52 |
| | | |
| 3 | FIRST ROW | | 1 | 52 | 4
(0)| 00:00:01 | | |
| 4 | INDEX RANGE SCAN (MIN/MAX)| IDX1 | 1 | 52 | 4 (0)|
00:00:01 | KEY | KEY |
----------------------------------------------------------------------------------------------------------------
On Tue, Sep 21, 2021 at 12:02 PM ahmed.fikri@xxxxxxxxxxx
<mailto:ahmed.fikri@xxxxxxxxxxx> <ahmed.fikri@xxxxxxxxxxx
<mailto:ahmed.fikri@xxxxxxxxxxx> > wrote:
Hi,
pragmatically I used to solve these problems (in my opinion oracle bugs)
by creating a scheduler job to detect and remove the SQLs, that cause
such problems, from the shared pool (using dbms_shared_pool.purge).
Since one can not change the vendor's code.
Best regards
Ahmed
-----Original-Nachricht-----
Betreff: shared pool waits
Datum: 2021-09-20T21:25:36+0200
Von: "Pap" <oracle.developer35@xxxxxxxxx
<mailto:oracle.developer35@xxxxxxxxx> >
An: "Oracle L" <oracle-l@xxxxxxxxxxxxx <mailto:oracle-l@xxxxxxxxxxxxx> >
Hi , We have a customer application in which we see high wait events like
'cursor:mutex ' and 'library cache lock' for a select query occasionally
and thus a specific functionality impacted. This select query(which is
part of a plsql procedure) is quick query which runs ~5 million times/hr.
But even though number of execution is same mostly throughout the day, it
still went through these odd wait events making the per execution time
went higher for around ~15 minutes duration causing slowness. And during
this period, the ASH shows fro this query, the value of column
in_hard_parse as 'N' but in_parse as 'Y' and 'N' both. And we saw we were
having stats gather running on that base object during same time. We have
no_invalidate set as 'FALSE" as table stats preference, So wanted to
understand from experts, can it be really because of 'parsing' issue and
we should delete this no_invalidate preference so that it can inherit the
default global preference i.e no_invalidate=>auto? The database version
is 19C.
