RE: Tuning Self-referencing Inserts
Date: Sun, 2 Dec 2018 12:27:28 -0500
Message-ID: <02c901d48a64$64d52540$2e7f6fc0$_at_rsiz.com>
Just quick random thoughts:
Parallel or serial? (Both any select feeding this and Parallel DML)
On RAC, using force local parallel?
Is there a reason the insert has not been arranged to be append? (Hard to see if there is a logical impediment with the SQL truncated).
After the dominant DB CPU wait, the SQL net wait from DBLINK seems interesting. What's that about?
Decoupling the analysis of select time and insert time is often useful, where are the values coming from?
When using conventional insert the search for available space in existing blocks can time considerable time. Depending on the mode of the cloning, you may find that this issue is erased from the destination system. If this is some sort of physical clone, no worries, but if the table has been reloaded the list of blocks with room for just one more or a few rows shoved back on the (freelist or freespace bitmap) has been removed as well as any issue with delayed block cleanout.
Any of the table rebuilding exercises done on the RAC would quickly eliminate this possibility of root cause and provide a possibly improved difference between RAC and non-RAC. Setting pctused to 0 would prevent a re-occurrence IF that is the problem, possibly leading to a periodic copy out keep maintenance IF space lost to accumulated deleted space becomes significant.
"Empty front" resulting from completely empty blocks at the beginning of the table that are late on the next up freelist or freespace bitmap can exhibit these symptoms of huge numbers of blocks read to get very few rows, but that doesn't show up for indexed access, just fts. Which object is getting all those reads?
That surely seems like a pantload of db file reads! Is that just this operation, and how was that stat list produced?
mwf
From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org]
On Behalf Of MacGregor, Ian A. (Redacted sender "ian" for DMARC)
Sent: Sunday, December 02, 2018 1:18 AM
To: dmarc-noreply_at_freelists.org; andysayer_at_gmail.com
Cc: ORACLE-L
Subject: Re: Tuning Self-referencing Inserts
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_at_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<-qerhjInn
erProbeHashTable()+491<-kdstf11001010000km()+617<-kdsttgr()+103608<-qertbFet
ch()+2455<-rwsfcd()+103<-qerhjFetch()+621<-qerjotFetch()+2025<-qerjotFetch()
+2025<-qerghFetch()+315<-rwsfcd()+103<-qerltcFetch()+1223<-insexe()+691<-opi
exe()+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_at_freelists.org <oracle-l-bounce_at_freelists.org> on
behalf of Andy Sayer <andysayer_at_gmail.com>
Sent: Friday, November 30, 2018 2:56:28 PM
To: dmarc-noreply_at_freelists.org
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_at_freelists.org> 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.
--
http://www.freelists.org/webpage/oracle-l
Received on Sun Dec 02 2018 - 18:27:28 CET