Re: Re: Tuning Self-referencing Inserts

From: <l.flatz_at_bluewin.ch>
Date: Mon, 3 Dec 2018 12:57:41 +0100 (CET)
Message-ID: <1894414073.21745.1543838261258.JavaMail.webmail_at_bluewin.ch>

Hi,
the estimates in this plan are incoreect. If they were correct, the statement would be much faster. Regards
Lothar
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Von : dmarc-noreply_at_freelists.org
Datum : 02/12/2018 - 07:17 (MN)
An : dmarc-noreply_at_freelists.org, andysayer_at_gmail.com Cc : oracle-l_at_freelists.org
Betreff : Re: Tuning Self-referencing Inserts P {

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The table is very small about 64K. Here is an explain plan from a month ago.

| 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<-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

1.2

User I/O

control file sequential read

149,191

96.6

System I/O

direct path read

71,377

89.5

User I/O

SQL*Net more data to dblink

45,096

51.1

Network

log switch/archive

43.8

2086

Other

recovery area: computing obsolete files

22.3

2234

Other

log file sync

33,439

19.2

Commit

gc current block 2-way

42,984

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.

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Received on Mon Dec 03 2018 - 12:57:41 CET

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