Ian,
I wrote a PL/SQL package called ASH_XPLAN
<http://evdbt.com/download/presentation-real-time-sql-tuning-delivered-at-hotsos-symposium-2015-and-utoug-training-days-2015/>
that combines DBMS_XPLAN with information from V$ACTIVE_SESSION_HISTORY
to accumulate the ASH time spent in each step of the execution plan of a
presently-running SQL statement. By running ASH_XPLAN in a separate
SQL*Plus session repeatedly, I can see which way the wind blows in a
very short time, without having to wait for the statement to complete.
Of course, please don't consider accumulated ASH time to be exactly
equal to elapsed time, as explained by Graham, Uri, and JB
<http://www.rmoug.org/wp-content/uploads/QEW_Presentations/2012/ASH%20Architecture%20and%20Advanced%20Usage.pdf>.
I'm aware that the DBMS_SQLTUNE and SQL Monitor functionality (thanks
Tim Hall!)
<https://oracle-base.com/articles/11g/real-time-sql-monitoring-11gr1> in
views like V$SQL_PLAN_STATISTICS does this as well, but I found it fun
and educational to solve the problem myself. I was lonely for a nice
PL/SQL project that week. :)
Either way, using ASH_XPLAN or DBMS_SQLTUNE, I strongly recommend
displaying the actual elapsed time for each step of the plan in an
actual execution to determine where the most time is being spent.
Nothing really matters in optimization except elapsed time, everything
else is explanatory information.
Elapsed time (a.k.a. "life") is too short for guessing.
Hope this helps...
-Tim
On 12/1/18 22:17, MacGregor, Ian A. (Redacted sender ian for DMARC) wrote:
The table is very small about 64K. Here is an explain plan from a month ago.
-------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-------------------------------------------------------------------------------------------------------
| 0 | INSERT STATEMENT | | | | 2999 (100)| |
| 1 | LOAD TABLE CONVENTIONAL | | | | | |
| 2 | HASH UNIQUE | | 1 | 477 | 2999 (1)| 00:00:36 |
| 3 | NESTED LOOPS | | 1 | 477 | 2994 (1)| 00:00:36 |
| 4 | NESTED LOOPS | | 192 | 477 | 2994 (1)| 00:00:36 |
|* 5 | HASH JOIN | | 2 | 254 | 6 (0)| 00:00:01 |
| 6 | NESTED LOOPS | | 8 | 608 | 3 (0)| 00:00:01 |
|* 7 | TABLE ACCESS FULL | PS_PSA_RULES_HDR | 8 | 504 | 3 (0)| 00:00:01 |
|* 8 | INDEX UNIQUE SCAN | PS_PSA_RULES_LVL | 1 | 13 | 0 (0)| |
|* 9 | TABLE ACCESS FULL | PS_PSA_RULES_LN | 32 | 1632 | 3 (0)| 00:00:01 |
|* 10 | INDEX RANGE SCAN | PS_PSA_ACCTG_TA34 | 96 | | 1473 (1)| 00:00:18 |
|* 11 | INDEX RANGE SCAN | PS_PSA_ACCTDSTGL4 | 1 | 20 | 2 (0)| 00:00:01 |
|* 12 | INDEX RANGE SCAN | PS_PSA_ACCTDSTGL4 | 1 | 14 | 2 (0)| 00:00:01 |
| 13 | SORT AGGREGATE | | 1 | 19 | | |
| 14 | TABLE ACCESS BY INDEX ROWID| PS_PSA_ACCTDSTGL4 | 1 | 19 | 3 (0)| 00:00:01 |
|* 15 | INDEX RANGE SCAN | PS_PSA_ACCTDSTGL4 | 1 | | 2 (0)| 00:00:01 |
|* 16 | TABLE ACCESS BY INDEX ROWID | PS_PSA_ACCTG_TA34 | 1 | 350 | 1494 (1)| 00:00:18 |
-------------------------------------------------------------------------------------------------------
It took just over 11,000 seconds to insert 25,000 rows There were 1,509,2 87,736 buffer gets associated with the instance. There is something definitely wrong. This is a 2-node RAC system. FYI the insert is called more than once. It runs pretty well the first time then gets dramatically worse. The above is the second worse case from about a month ago. There doesn't seem to be anything wrong with SQL
For the latest run, I decided to do periodic probes of v$session wait. Each time I did I saw the library cache pin wait all with "waited short time". V$session did not show any blocking session. Neither did the query tailored to find blockers for this wait. I did a system state dump
-------------------------------------------------------------------------------
Oracle session identified by:
{
instance: 1 (fsprd.fsprd1)
os id: 28554
process id: 176, oracle@erp-fprd-oracle01
session id: 406
session serial #: 251
}
is not in a wait:
{
last wait: 120 min 20 sec ago
blocking: 0 sessions
current sql: INSERT INTO PS_PSA_ACCTDSTGL4 (PROCESS_INSTANCE, BUSINESS_UNIT_PC, PROJECT_ID, ACTIVITY_ID, RESOURCE_ID, LINE_SEQ_NBR, DEBIT_CREDIT, DST_USE, INTER_ORG_LEVEL, CONVERSION_RATE, ORG_TO_BOOK, COMBO_STATUS, PROJECT_FLAG, IU_ANCHOR_FLG, CONTRACT_NUM, CONTRACT_LINE_NUM, CONTRACT_PPD_SEQ, ACCT_PLAN_ID, EVENT_NUM, ACCOUNT, AL
short stack: ksedsts()+465<-ksdxfstk()+32<-ksdxcb()+1927<-sspuser()+112<-__sighandler()<-qerixtFetch()+547<-subex1()+259<-subsr3()+183<-evaopn3()+2533<-expepr()+576<-evaiand()+51<-expeal()+23<-qerixtFetch()+800<-qerjotRowProc()+359<-qerhjInnerProbeHashTable()+491<-kdstf11001010000km()+617<-kdsttgr()+103608<-qertbFetch()+2455<-rwsfcd()+103<-qerhjFetch()+621<-qerjotFetch()+2025<-qerjotFetch()+2025<-qerghFetch()+315<-rwsfcd()+103<-qerltcFetch()+1223<-insexe()+691<-opiexe()+5632<-kpoal8()+2380<-opiodr()+917<-ttcpip()+2183<-opitsk(
wait history:
1. event: 'library cache pin'
time waited: 0.000158 sec
wait id: 7433154 p1: 'handle address'=0x9c48940d0
p2: 'pin address'=0x5eec1bd08
p3: '100*mode+namespace'=0x41cdd00010002
* time between wait #1 and #2: 0.000046 sec
2. event: 'library cache lock'
time waited: 0.000228 sec
wait id: 7433153 p1: 'handle address'=0x9c48940d0
p2: 'lock address'=0x5eeef6eb0
p3: '100*mode+namespace'=0x41cdd00010002
* time between wait #2 and #3: 0.000516 sec
3. event: 'library cache pin'
time waited: 0.000250 sec
wait id: 7433152 p1: 'handle address'=0x9a2fdaf10
p2: 'pin address'=0x99a42e960
p3: '100*mode+namespace'=0x2160300010002
}
==========================================================================================
I thought the lock/pin was against an index, but the 100 indicates it is against the table. However despite their showing up when I probed v$session_wait they are not shown to be a significant wait. I was surprised to see them however, because I associated such locks/pins with DDL not DML.
The last point is that this is a 2 node RAC system, the database was cloned to a single instance database and the program ran much more efficiently. The longest time for an insert statement was less than an hour.
Here are the RAC stats from the run done about a month ago. This covers a 10 hour period
The top RAC associated wait was ranked 10th
* *•*
*Event*
*Waits*
*Total Wait Time (sec)*
*Wait Avg(ms)*
*% DB time*
*Wait Class*
DB CPU
38K
96.6
SQL*Net message from dblink
3,038
497.6
164
1.3
Network
db file sequential read
1,233,886
474.4
0
1.2
User I/O
control file sequential read
149,191
96.6
1
.2
System I/O
direct path read
71,377
89.5
1
.2
User I/O
SQL*Net more data to dblink
45,096
51.1
1
.1
Network
log switch/archive
21
43.8
2086
.1
Other
recovery area: computing obsolete files
10
22.3
2234
.1
Other
log file sync
33,439
19.2
1
.0
Commit
gc current block 2-way
42,984
16
0
.0
Cluster
The db link wait is not associated with this process.
Ian A. MacGregor
SLAC National Accelerator Laboratory
Computing Division
To offer the best IT service at the lab and be the IT provider of choice.
------------------------------------------------------------------------
*From:* oracle-l-bounce@xxxxxxxxxxxxx <oracle-l-bounce@xxxxxxxxxxxxx> on behalf of Andy Sayer <andysayer@xxxxxxxxx>
*Sent:* Friday, November 30, 2018 2:56:28 PM
*To:* dmarc-noreply@xxxxxxxxxxxxx
*Cc:* ORACLE-L
*Subject:* Re: Tuning Self-referencing Inserts
I think we need to take a few steps back.
It’s hard to explain why such a statement would cause noticeable issues if the table is really not that large. A simple insert into <target> statement using a select from <target table>, won’t take a silly amount of time - it’s just the time to read the table blocks using a full tablescan then the time to update the indexes which might be some overhead but no different to any other insert statement of the same volume.
Perhaps this this insert is within some loop? Perhaps the self-reference is written so that a silly execution plan is being used. It would be great if you could share the execution plan you are seeing and the SQL being executed. Is there PL/SQL involved?
One other thing that springs to mind that could have an impact is DML error logging (it sounds like a situation where unique keys could give you errors?)
As for library cache pins, this is unusual for an insert/select statement. Things like running a PL/SQL procedure which another session is trying to recompile while another session is executing it will bring around this behaviour. Perhaps there is a function being called by your statement. Again, what exactly are you seeing? This is a block so you should be able to investigate what the blocking session is doing by checking v$session.
Hope this helps,
Andy
On Fri, 30 Nov 2018 at 18:32, MacGregor, Ian A. <dmarc-noreply@xxxxxxxxxxxxx <mailto:dmarc-noreply@xxxxxxxxxxxxx>> wrote:
The problem is with a PeopleSoft statement which is based on a
select statement which references the table being inserted. The
problem stems from having to read and build the indexes of the
table which is not that large. The buffer gets are extremely high.
Is there generic answer to this problem. Would it help to
rebuild with a higher percent free in an attempt to have few
rows per block so as to lessen contention.
Also for library cache pins I don't understand how to reads the
p3raw value. I think the problem primarily lies with the
maintenance m of the unique index bit I am. not 100% confident.
Ian A. MacGregor
SLAC National Accelerator Laboratory
Computing Division
To offer the best IT service at the lab and be the IT provider of
choice.
