Buggy overhead of SQL Plan Baseline Capture

There’s at least one bug related to the performance overhead of SQL Baseline Capture and ASH is less than clear with recursive SQL

First up – apologies, I’ve not got a reproducible test case because I flushed the shared pool between tests and the whole performance degradation scenario disappeared. I should have known when one of the Metalink notes talked about the problem disappearing when bouncing the instance that I shouldn’t have touched the shared pool. Now I can’t reproduce. I’m going to keep trying, but for now, let me tell you what I’ve got (I am trying to be more precise in my blogging but yet again it’s something woolly or nothing).

With that out the way, we’re in the initial stages of an upgrade from 9.2.0.8 on 32-bit Solaris to 11.2.0.2 on 64-bit Linux, a one-step all-or-nothing change-everything at once upgrade.

Plan was to run with optimizer_features_enable set to 9.2.0, various other parameters set to current production settings and to capture 9i plans into a baseline.

Initial runs of “The Batch” started, all processes reported as slow. The initial major contributor turns out to be recursive SQL related to SQL Plan Baseline Capture (see bug#11600319, also bug #11719151 and doc id 1295054.1 – thanks to Timur Akhmadeev for the pointers)

I haven’t yet raised this with Oracle Support because a) I can’t face the wait for a response and b) local red tape means that patches need to be approved by the DB Engineering team and approval for non-production environments is difficult (I’m not going there, not now).

Bug # 11719151 – “RECURSIVE MERGE WHEN optimizer_capture_sql_plan_baseline=true DOING FTS” – is certainly relevant.
The MERGE statement into SQLOBJ$AUXDATA does use a FULL TABLE SCAN. But if I were to show you the AWR reports then you’d see the MERGE statement into SQLOBJ$DATA was the bigger problem and the MERGE statement into SQLOBJ$ also not insignificant.

Pick a metric, any metric:
3 out of the top 10 by Elapsed Time, 2 out of the top 5, 1 of the top 1.

        Elapsed                  Elapsed Time
        Time (s)    Executions  per Exec (s)  %Total   %CPU    %IO    SQL Id
---------------- -------------- ------------- ------ ------ ------ -------------
         6,481.5        242,111          0.03   43.2   22.6   56.1 1vxm21mhmgy07
MERGE INTO sqlobj$data USING dual ON (:1 IS NULL) WHEN MATCHED THEN UPDATE SET comp_data = :2 WHERE

         2,403.4        242,108          0.01   16.0   95.4    3.9 44z7snw61qx9x
MERGE INTO sqlobj$auxdata USING dual ON (:1 IS NULL) WHEN MATCHED THEN UPDATE SET description = :2,

           898.7        242,111          0.00    6.0   98.6     .1 7xm5j53mxbtpn
MERGE INTO sqlobj$ USING dual ON (:1 IS NULL) WHEN MATCHED THEN UPDATE SET name = :2,

By CPU Time:

    CPU                   CPU per           Elapsed
  Time (s)  Executions    Exec (s) %Total   Time (s)   %CPU    %IO    SQL Id
---------- ------------ ---------- ------ ---------- ------ ------ -------------
   2,292.8      242,108       0.01   39.9    2,403.4   95.4    3.9 44z7snw61qx9x
MERGE INTO sqlobj$auxdata USING dual ON (:1 IS NULL) WHEN MATCHED THEN UPDATE SET description = :2,


   1,464.0      242,111       0.01   25.5    6,481.5   22.6   56.1 1vxm21mhmgy07
MERGE INTO sqlobj$data USING dual ON (:1 IS NULL) WHEN MATCHED THEN UPDATE SET comp_data = :2 WHERE

     885.7      242,111       0.00   15.4      898.7   98.6     .1 7xm5j53mxbtpn
MERGE INTO sqlobj$ USING dual ON (:1 IS NULL) WHEN MATCHED THEN UPDATE SET name = :2,

By Gets:

     Buffer                 Gets              Elapsed
      Gets   Executions   per Exec   %Total   Time (s)   %CPU    %IO    SQL Id
----------- ----------- ------------ ------ ---------- ------ ------ -----------
 49,599,141     242,108        204.9   46.9    2,403.4   95.4    3.9 44z7snw61qx
MERGE INTO sqlobj$auxdata USING dual ON (:1 IS NULL) WHEN MATCHED THEN UPDATE SET description = :2,

 29,107,449     242,111        120.2   27.5    6,481.5   22.6   56.1 1vxm21mhmgy
MERGE INTO sqlobj$data USING dual ON (:1 IS NULL) WHEN MATCHED THEN UPDATE SET comp_data = :2 WHERE

 16,671,818     242,111         68.9   15.7      898.7   98.6     .1 7xm5j53mxbt
MERGE INTO sqlobj$ USING dual ON (:1 IS NULL) WHEN MATCHED THEN UPDATE SET name = :2,

By executions:

 Executions   Rows Processed  Rows per Exec   Time (s)   %CPU    %IO    SQL Id
------------ --------------- -------------- ---------- ------ ------ -----------
     242,111         242,111            1.0    6,481.5   22.6   56.1 1vxm21mhmgy
MERGE INTO sqlobj$data USING dual ON (:1 IS NULL) WHEN MATCHED THEN UPDATE SET comp_data = :2 WHERE

     242,111         242,111            1.0      898.7   98.6     .1 7xm5j53mxbt
MERGE INTO sqlobj$ USING dual ON (:1 IS NULL) WHEN MATCHED THEN UPDATE SET name = :2,


     242,111         242,074            1.0       34.6   95.7     .2 9zr2sbbp1d4
SELECT /*+ INDEX(sqlobj$ (name obj_type)) */ signature, category 
FROM sqlobj$ WHERE name = :1 AND obj_type = :2

     242,108         242,108            1.0    2,403.4   95.4    3.9 44z7snw61qx
MERGE INTO sqlobj$auxdata USING dual ON (:1 IS NULL) WHEN MATCHED THEN UPDATE SET description = :2,

So, you get the message.

Furthermore, at the top of every Segment Statistic by X Metric, it’s either one of the LOBs or the LOB Index related to these three tables.

By the way, what’s in these SQLOBJ$ tables – no surprises it’s the baseline data.
See also:
Kerry Osborne – Do SQL Baselines Use Hints/
Christian Antognini – SQL Profiles in the Data Dictionary
Christian Antognini – Troubleshooting Oracle Performance

If I move over to the ASH data and give an example of what that was showing, then we can go and look at those SQLOBJ$ tables for the SQL concerned.

The ASH data – probably my most favorite feature of the last few years – I’m only displaying a little bit of in terms of height and width. But it illustrates the second point I wanted to highlight – that recursive SQL is not properly reported. Whilst the SQL_ID column differs from the TOP_LEVEL_SQL_ID (which I’ve omitted to keep it slim), this is still the SQL Id of a nested lookup, not the SQL Id of the recursive MERGE which you might have expected – I can see pros and cons of both I suppose.

  1  select to_char(sample_time,'HH24:MI:SS') sample_time, session_id, sql_id
  2  ,      sql_plan_operation, event
  3  from   v$active_session_history
  4  where  session_id      = 1388
  5  and    session_serial# = 147
  6  and    sample_id between 14596749 and 14596800
  7* order by sample_id
SQL> /

SAMPLE_T SESSION_ID SQL_ID        SQL_PLAN_OPERATION             EVENT
-------- ---------- ------------- ------------------------------ -----------------------------------
10:57:04       1388 d99anrdgbb4jf SELECT STATEMENT
10:57:05       1388                                              log file sync
10:57:06       1388 d99anrdgbb4jf
10:57:07       1388 d99anrdgbb4jf MERGE                          direct path write
10:57:08       1388 d99anrdgbb4jf MERGE                          flashback log file sync
10:57:09       1388 d99anrdgbb4jf                                direct path read
10:57:10       1388 d99anrdgbb4jf MERGE                          buffer busy waits
10:57:11       1388 d99anrdgbb4jf SELECT STATEMENT               latch: shared pool
10:57:12       1388 d99anrdgbb4jf MERGE                          direct path read
10:57:13       1388 d99anrdgbb4jf TABLE ACCESS
10:57:14       1388 d99anrdgbb4jf INDEX
10:57:15       1388 d99anrdgbb4jf MERGE                          direct path write
10:57:16       1388 d99anrdgbb4jf TABLE ACCESS
10:57:17       1388 d99anrdgbb4jf TABLE ACCESS
10:57:18       1388 d99anrdgbb4jf                                direct path read
10:57:19       1388 d99anrdgbb4jf TABLE ACCESS
10:57:20       1388 d99anrdgbb4jf MERGE
10:57:21       1388                                              log file sync
10:57:22       1388                                              log file sync
10:57:23       1388 d99anrdgbb4jf MERGE                          direct path write
10:57:24       1388 d99anrdgbb4jf MERGE                          direct path write
10:57:25       1388 d99anrdgbb4jf TABLE ACCESS
10:57:26       1388 d99anrdgbb4jf                                direct path read
10:57:27       1388 d99anrdgbb4jf                                direct path read
10:57:28       1388 d99anrdgbb4jf MERGE                          db file sequential read
10:57:29       1388 d99anrdgbb4jf MERGE
10:57:30       1388                                              log file sync
10:57:31       1388 d99anrdgbb4jf MERGE                          db file sequential read
10:57:32       1388 d99anrdgbb4jf MERGE
10:57:33       1388 d99anrdgbb4jf INDEX
10:57:34       1388 d99anrdgbb4jf MERGE                          buffer busy waits
10:57:35       1388 d99anrdgbb4jf MERGE                          buffer busy waits
10:57:36       1388 d99anrdgbb4jf MERGE                          flashback log file sync
10:57:37       1388 d99anrdgbb4jf MERGE                          direct path write
10:57:38       1388 d99anrdgbb4jf MERGE                          db file sequential read
10:57:39       1388 d99anrdgbb4jf MERGE                          db file sequential read
10:57:40       1388 d99anrdgbb4jf MERGE                          buffer busy waits
10:57:41       1388 d99anrdgbb4jf MERGE                          enq: TX - index contention
10:57:42       1388 d99anrdgbb4jf MERGE                          buffer busy waits
10:57:43       1388 d99anrdgbb4jf MERGE                          db file sequential read
10:57:44       1388 d99anrdgbb4jf MERGE                          db file sequential read
10:57:45       1388                                              log file sync
10:57:46       1388 d99anrdgbb4jf TABLE ACCESS
10:57:47       1388 d99anrdgbb4jf MERGE                          flashback log file sync
10:57:48       1388 d99anrdgbb4jf MERGE JOIN
10:57:49       1388 d99anrdgbb4jf MERGE                          db file sequential read
10:57:50       1388 d99anrdgbb4jf MERGE                          db file sequential read
10:57:51       1388 d99anrdgbb4jf TABLE ACCESS
10:57:52       1388 d99anrdgbb4jf MERGE                          direct path write
10:57:53       1388 d99anrdgbb4jf TABLE ACCESS
10:57:54       1388 d99anrdgbb4jf MERGE                          db file sequential read
10:57:55       1388 d99anrdgbb4jf SELECT STATEMENT

52 rows selected.

SQL> 

By the way, I was also a little surprised to see the direct path read/write operations in the ASH data but these SQLOBJ$ tables that we’re constantly MERGING into recursively have LOBS and further investigation revealed these events to be associated with those LOB segments.

As you can see from above, lots of MERGE operations which have nothing directly to do with SQL_ID d99anrdgbb4jf which looks like the statement below. By the time I’ve got to some of this data for the purposes of this, it’s gone from V$SQL so I’m fetched it from AWR.

SQL> select * from table(dbms_xplan.display_awr('d99anrdgbb4jf'));

PLAN_TABLE_OUTPUT
-----------------------------------------------------------------------------------
SQL_ID d99anrdgbb4jf
--------------------
SELECT XXXX_XXX FROM XXXX_XXXX WHERE XXXX_XXXX = 'MSD' AND XXXX_XXXX =:B1

Plan hash value: 878181930

-------------------------------------------------------------------------------
| Id  | Operation                   | Name            | Rows  | Bytes | Cost  |
-------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |                 |       |       |     2 |
|   1 |  TABLE ACCESS BY INDEX ROWID| XXXX_XXXX       |     1 |    18 |     2 |
|   2 |   INDEX RANGE SCAN          | XXXX_XXXX_IDX_1 |     1 |       |     2 |
-------------------------------------------------------------------------------

Note
-----
   - cpu costing is off (consider enabling it)

19 rows selected.

SQL> 

Baselines are stored according to signature. SQL statements have hash_values, sql ids and also exact/force matching signatures. By the way, the latter can be translated from the text of the sql statement using DBMS_SQLTUNE.SQLTEXT_TO_SIGNATURE using the FORCE_MATCH parameter for either the exact or force matching signature.

In AWR, we’ve only got the FORCE_MATCHING_SIGNATURE of this sql statement sql_id ‘d99anrdgbb4jf’ but take it was the same as the EXACT_MATCHING_SIGNATURE.

SQL> select distinct sql_id, force_matching_signature, to_char(force_matching_signature)
  2  from dba_hist_sqlstat 
  3  where sql_id = 'd99anrdgbb4jf'; 

SQL_ID        FORCE_MATCHING_SIGNATURE TO_CHAR(FORCE_MATCHING_SIGNATURE)
------------- ------------------------ ----------------------------------------
d99anrdgbb4jf               3.9882E+17 398819076860959259

SQL> 

I used this signature to see what was happening with the baseline data.

There’s not much point in me pasting the outputs of those tables. I could see that the SYS.SQLOBJ$.LAST_EXECUTED, SYS.SQLOBJ$AUXDATA.CREATED (!?!) and SYS.SQLOBJ$AUXDATA.LAST_MODIFIED were being updated although not the additional metrics like BUFFER_GETS, EXECUTIONS, etc in SYS.SQLOBJ$DATA.

But then I flushed the cache and like that … the performance degradation was gone and not reproducible… for now.

That’s all there is really.

Oh, by the way, I did trace one session while it was reproducing. Below are some of the relevant bits.
I was using a simple slow-by-slow lookup because I was then going to use concurrent sessions which initially were causing me problems with SMO rowcache lock contention – quite possibly related again to the baselines, but I never got that far into the investigation before we flashed it all back and turned off capture.
Also, looping lookups were relevant to one of the bug notes above and are very much representative of some of the legacy Pro*C codebase.

...
BEGIN
 DBMS_OUTPUT.DISABLE;
 FOR r IN (SELECT * FROM t1)
 LOOP
     FOR x IN (SELECT id FROM t1 WHERE code = r.code)
     LOOP
       DBMS_OUTPUT.PUT_LINE(x.id);
     END LOOP;
 END LOOP;
END;

call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.01       0.01          0          0          0           0
Execute      1      1.07       1.10          0          0          0           0
Fetch        0      0.00       0.00          0          0          0           0
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total        2      1.08       1.11          0          0          0           0

Misses in library cache during parse: 1
Optimizer mode: CHOOSE
Parsing user id: 4106  

Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  SQL*Net break/reset to client                   2        0.00          0.00
  SQL*Net message to client                       1        0.00          0.00
  SQL*Net message from client                     1        0.00          0.00
  log file sync                                   1        0.06          0.06
********************************************************************************

....

SQL ID: 0jjc60pmrntdv
Plan Hash: 3617692013
SELECT * 
FROM
 T1


call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.00       0.00          0          0          1           0
Execute      1      0.00       0.00          0          0          0           0
Fetch       66      0.01       0.01          0        279          0        6600
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total       68      0.01       0.02          0        279          1        6600

Misses in library cache during parse: 1
Optimizer mode: CHOOSE
Parsing user id: 4106     (recursive depth: 1)

Rows     Row Source Operation
-------  ---------------------------------------------------
   6600  TABLE ACCESS FULL T1 (cr=279 pr=0 pw=0 time=13232 us cost=498 size=22700000 card=100000)

********************************************************************************

SQL ID: 33kddu0j5ykq6
Plan Hash: 2946553998
SELECT ID 
FROM
 T1 WHERE CODE = :B1 


call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.00       0.00          0          0          0           0
Execute   6507     18.15      37.59       6504      54980       6523           0
Fetch     6506      0.28       0.28          0      26024          0        6506
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total    13014     18.43      37.88       6504      81004       6523        6506

Misses in library cache during parse: 1
Misses in library cache during execute: 1
Optimizer mode: CHOOSE
Parsing user id: 4106     (recursive depth: 1)

Rows     Row Source Operation
-------  ---------------------------------------------------
      1  TABLE ACCESS BY INDEX ROWID T1 (cr=4 pr=0 pw=0 time=233 us cost=2 size=26 card=1)
      1   INDEX UNIQUE SCAN I1 (cr=3 pr=0 pw=0 time=211 us cost=1 size=0 card=1)(object id 97386)


Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  latch: cache buffers chains                    22        0.00          0.00
  library cache: mutex X                          4        0.00          0.00
  latch: shared pool                              8        0.00          0.00
********************************************************************************

SQL ID: 9zr2sbbp1d4fs
Plan Hash: 2462756431
SELECT /*+ INDEX(sqlobj$ (name obj_type)) */ signature, category              
FROM
 sqlobj$                                                                  
  WHERE name = :1                                                             
          AND obj_type = :2


call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse      435      0.01       0.01          0          0          0           0
Execute    435      0.06       0.06          0          0          0           0
Fetch      435      0.01       0.02          1        871          0         434
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total     1305      0.09       0.10          1        871          0         434

Misses in library cache during parse: 1
Misses in library cache during execute: 1
Optimizer mode: CHOOSE
Parsing user id: SYS   (recursive depth: 2)

Rows     Row Source Operation
-------  ---------------------------------------------------
      0  INDEX RANGE SCAN I_SQLOBJ$NAME_TYPE (cr=3 pr=1 pw=0 time=10195 us cost=1 size=54 card=1)(object id 199)


Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  Disk file operations I/O                        1        0.00          0.00
  db file sequential read                         1        0.00          0.00
********************************************************************************

SQL ID: 47y3mqvyhpkvs
Plan Hash: 1888265482
SELECT obj_type, plan_id, name, flags, last_executed                          
FROM
 sqlobj$                                                                  
  WHERE signature = :1                                                        
          AND category = :2


call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.00       0.00          0          0          0           0
Execute      1      0.00       0.00          0          0          0           0
Fetch        1      0.00       0.00          0          2          0           0
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total        3      0.00       0.00          0          2          0           0

Misses in library cache during parse: 1
Misses in library cache during execute: 1
Optimizer mode: CHOOSE
Parsing user id: SYS   (recursive depth: 2)

Rows     Row Source Operation
-------  ---------------------------------------------------
      0  INDEX RANGE SCAN SQLOBJ$_PKEY (cr=2 pr=0 pw=0 time=51 us cost=1 size=74 card=1)(object id 198)

********************************************************************************

....

SQL ID: 7xm5j53mxbtpn
Plan Hash: 2110601055
MERGE INTO sqlobj$                                                            
  USING dual ON (:1 IS NULL)                                                  
    WHEN MATCHED THEN                                                         
        UPDATE SET name = :2,                                                 
                     flags = :3,                                              
                       last_executed = :4                                     
              WHERE signature = :5                                            
                      AND category = :6                                       
                        AND obj_type = :7                                     
                          AND plan_id = :8                                    
                    WHEN NOT MATCHED THEN                                     
                        INSERT (signature, category, obj_type, plan_id, name, 
                                  flags, last_executed)                       
                            VALUES (:9, :10, :11, :12, :13, :14, :15)


call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse     6505      0.35       0.37          0          0          0           0
Execute   6505     29.78      31.78         52     430259      13126        6505
Fetch        0      0.00       0.00          0          0          0           0
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total    13010     30.13      32.16         52     430259      13126        6505

Misses in library cache during parse: 1
Misses in library cache during execute: 2
Optimizer mode: CHOOSE
Parsing user id: SYS   (recursive depth: 2)

Rows     Row Source Operation
-------  ---------------------------------------------------
      0  MERGE  SQLOBJ$ (cr=2 pr=0 pw=0 time=748 us)
      1   VIEW  (cr=2 pr=0 pw=0 time=202 us)
      1    MERGE JOIN OUTER (cr=2 pr=0 pw=0 time=198 us cost=7 size=162488 card=2138)
      1     TABLE ACCESS FULL DUAL (cr=2 pr=0 pw=0 time=169 us cost=2 size=2 card=1)
      0     VIEW  (cr=0 pr=0 pw=0 time=7 us cost=5 size=158212 card=2138)
      0      FILTER  (cr=0 pr=0 pw=0 time=3 us)
      0       INDEX FAST FULL SCAN SQLOBJ$_PKEY (cr=0 pr=0 pw=0 time=0 us cost=9 size=158212 card=2138)(object id 198)


Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  latch: cache buffers chains                    23        0.00          0.00
  db file sequential read                        52        0.89          1.03
  buffer busy waits                              65        0.00          0.00
  log file switch completion                      4        0.24          0.44
  library cache: mutex X                          2        0.00          0.00
********************************************************************************

SQL ID: 44z7snw61qx9x
Plan Hash: 1133963577
MERGE INTO sqlobj$auxdata                                                     
  USING dual ON (:1 IS NULL)                                                  
    WHEN MATCHED THEN                                                         
        UPDATE SET description = :2,                                          
                     creator = nvl(:3, creator),                              
                       origin = :4,                                           
                         version = :5,                                        
                           created = :6,                                      
                             last_modified = :7,                              
                               last_verified = nvl(:8, last_verified),        
                                 parse_cpu_time = null,                       
                                   optimizer_cost = nvl(:9, optimizer_cost),  
                                     module = nvl(:10, module),               
                                       action = nvl(:11, action),             
                                         priority = nvl(:12, priority),       
                                           optimizer_env = nvl(:13, 
  optimizer_env),                                      bind_data = nvl(:14, 
  bind_data),                                              
  parsing_schema_name = nvl(:15, parsing_schema_name),                        
    executions = nvl(:16, executions),                                        
      elapsed_time = nvl(:17, elapsed_time),                                  
        cpu_time = nvl(:18, cpu_time),                                        
          buffer_gets = nvl(:19, buffer_gets),                                
            disk_reads = nvl(:20, disk_reads),                                
              direct_writes = nvl(:21, direct_writes),                        
                rows_processed = nvl(:22, rows_processed),                    
                  fetches = nvl(:23, fetches),                                
                    end_of_fetch_count = nvl(:24, end_of_fetch_count),        
                      task_id = nvl(:25, task_id),                            
                        task_exec_name = nvl(:26, task_exec_name),            
                          task_obj_id = nvl(:27, task_obj_id),                
                            task_fnd_id = nvl(:28, task_fnd_id),              
                              task_rec_id = nvl(:29, task_rec_id),            
                                flags = 0,                                    
                                  spare1 = null,                              
                                    spare2 = null                             
                           WHERE signature = :30                              
                                   AND category = :31                         
                                     AND obj_type = :32                       
                                       AND plan_id = :33                      
                                 WHEN NOT MATCHED THEN                        
                                     INSERT (signature, category, obj_type, 
  plan_id,                                       description, creator, origin,
   version,                                        created, last_modified, 
  last_verified, parse_cpu_time,                        optimizer_cost, 
  module, action, priority,                                     optimizer_env,
   bind_data, parsing_schema_name, executions,                    
  elapsed_time, cpu_time, buffer_gets, disk_reads,                            
    direct_writes, rows_processed, fetches,end_of_fetch_count,                
      task_id, task_exec_name, task_obj_id, task_fnd_id,                      
        task_rec_id, flags, spare1, spare2)                                   
  VALUES (:34, :35, :36, :37,                                                 
            :38, :39, :40, :41,                                               
              :42, :43, null, null,                                           
                :44, :45, :46, :47,                                           
                  :48, :49, :50, :51,                                         
                    :52, :53, :54, :55,                                       
                      :56, :57, :58, :59,                                     
                        :60, :61, :62, :63,                                   
                          :64, 0, null, null)


call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse     6504      0.47       0.49          0          0          0           0
Execute   6504     66.69      70.05        429    1631914      14302        6504
Fetch        0      0.00       0.00          0          0          0           0
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total    13008     67.16      70.55        429    1631914      14302        6504

Misses in library cache during parse: 1
Misses in library cache during execute: 2
Optimizer mode: CHOOSE
Parsing user id: SYS   (recursive depth: 2)

Rows     Row Source Operation
-------  ---------------------------------------------------
      0  MERGE  SQLOBJ$AUXDATA (cr=3 pr=0 pw=0 time=810 us)
      1   VIEW  (cr=2 pr=0 pw=0 time=134 us)
      1    MERGE JOIN OUTER (cr=2 pr=0 pw=0 time=122 us cost=18 size=784646 card=2138)
      1     TABLE ACCESS FULL DUAL (cr=2 pr=0 pw=0 time=91 us cost=2 size=2 card=1)
      0     VIEW  (cr=0 pr=0 pw=0 time=15 us cost=16 size=780370 card=2138)
      0      FILTER  (cr=0 pr=0 pw=0 time=2 us)
      0       TABLE ACCESS FULL SQLOBJ$AUXDATA (cr=0 pr=0 pw=0 time=0 us cost=20 size=780370 card=2138)


Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  Disk file operations I/O                        2        0.00          0.00
  db file sequential read                       429        0.29          2.56
  buffer busy waits                              58        0.00          0.00
  latch: cache buffers chains                    25        0.00          0.00
  log file switch completion                      1        0.05          0.05
  latch: object queue header operation            1        0.00          0.00
  library cache: mutex X                          2        0.00          0.00
********************************************************************************

SQL ID: 1vxm21mhmgy07
Plan Hash: 984916430
MERGE INTO sqlobj$data                                                        
  USING dual ON (:1 IS NULL)                                                  
    WHEN MATCHED THEN                                                         
        UPDATE SET comp_data = :2                                             
          WHERE signature = :3                                                
                  AND category = :4                                           
                    AND obj_type = :5                                         
                      AND plan_id = :6                                        
                WHEN NOT MATCHED THEN                                         
                    INSERT (signature, category, obj_type, plan_id, comp_data,
                              spare1, spare2)                                 
                        VALUES (:7, :8, :9, :10, :11, null, null)


call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse     6053      0.35       0.36          0          0          0           0
Execute   6053     38.42     192.12      14420     500403     235414        6053
Fetch        0      0.00       0.00          0          0          0           0
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total    12106     38.78     192.48      14420     500403     235414        6053

Misses in library cache during parse: 1
Misses in library cache during execute: 2
Optimizer mode: CHOOSE
Parsing user id: SYS   (recursive depth: 2)

Rows     Row Source Operation
-------  ---------------------------------------------------
      0  MERGE  SQLOBJ$DATA (cr=43 pr=2 pw=1 time=8478 us)
      1   VIEW  (cr=2 pr=0 pw=0 time=140 us)
      1    MERGE JOIN OUTER (cr=2 pr=0 pw=0 time=131 us cost=9 size=303596 card=2138)
      1     TABLE ACCESS FULL DUAL (cr=2 pr=0 pw=0 time=109 us cost=2 size=2 card=1)
      0     VIEW  (cr=0 pr=0 pw=0 time=5 us cost=7 size=299320 card=2138)
      0      FILTER  (cr=0 pr=0 pw=0 time=3 us)
      0       INDEX FAST FULL SCAN SQLOBJ$DATA_PKEY (cr=0 pr=0 pw=0 time=0 us cost=6 size=299320 card=2138)(object id 205)


Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  db file sequential read                      8367        1.04         43.76
  flashback log file sync                      7828        0.26         25.34
  direct path write                            6052        0.47         36.62
  direct path read                             6045        0.42         16.34
  enq: HW - contention                         1138        0.89         24.42
  Disk file operations I/O                       12        0.00          0.00
  latch: cache buffers chains                   860        0.00          0.03
  buffer busy waits                             764        1.00          6.00
  read by other session                          24        0.03          0.34
  latch: enqueue hash chains                      2        0.00          0.00
  enq: TX - index contention                     57        0.05          0.21
  buffer deadlock                                11        0.00          0.00
  latch free                                      2        0.00          0.00
  library cache: mutex X                          8        0.00          0.00
  latch: cache buffers lru chain                  4        0.00          0.00
  log file switch (checkpoint incomplete)         3        0.14          0.28
  enq: TX - allocate ITL entry                    1        0.00          0.00
  latch: undo global data                         1        0.00          0.00

.....


SQL ID: 1zatw56z32vcg
Plan Hash: 1469453527
SELECT obj_type, plan_id, description, creator, origin,                       
         created, last_modified                                               
    
FROM
 sqlobj$auxdata                                                           
  WHERE signature = :1                                                        
          AND category = :2


call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse     6505      0.10       0.12          0          0          0           0
Execute   6505      0.91       0.96          0          0          0           0
Fetch    13010      0.30       0.29          0      26020          0        6505
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total    26020      1.32       1.38          0      26020          0        6505

Misses in library cache during parse: 1
Misses in library cache during execute: 1
Optimizer mode: CHOOSE
Parsing user id: SYS   (recursive depth: 2)

Rows     Row Source Operation
-------  ---------------------------------------------------
      1  TABLE ACCESS BY INDEX ROWID SQLOBJ$AUXDATA (cr=4 pr=0 pw=0 time=87 us cost=2 size=315 card=1)
      1   INDEX RANGE SCAN I_SQLOBJ$AUXDATA_PKEY (cr=3 pr=0 pw=0 time=51 us cost=1 size=0 card=1)(object id 209)


Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  latch: cache buffers chains                     5        0.00          0.00
********************************************************************************

SQL ID: bt51szvfrcdpn
Plan Hash: 1876815449
SELECT obj_type, plan_id, comp_data                                           
FROM
 sqlobj$data                                                              
  WHERE signature = :1                                                        
          AND category = :2


call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse     6504      0.13       0.12          0          0          0           0
Execute   6504      0.82       0.82          0          0          0           0
Fetch    13008      0.28       0.32          0      19516          0        6504
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total    26016      1.24       1.27          0      19516          0        6504

Misses in library cache during parse: 1
Misses in library cache during execute: 1
Optimizer mode: CHOOSE
Parsing user id: SYS   (recursive depth: 2)

Rows     Row Source Operation
-------  ---------------------------------------------------
      1  INDEX RANGE SCAN SQLOBJ$DATA_PKEY (cr=3 pr=0 pw=0 time=89 us cost=1 size=140 card=1)(object id 205)


Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  latch: cache buffers chains                    17        0.00          0.00
********************************************************************************

SQL ID: 1vxm21mhmgy07
Plan Hash: 2462756431
MERGE INTO sqlobj$data                                                        
  USING dual ON (:1 IS NULL)                                                  
    WHEN MATCHED THEN                                                         
        UPDATE SET comp_data = :2                                             
          WHERE signature = :3                                                
                  AND category = :4                                           
                    AND obj_type = :5                                         
                      AND plan_id = :6                                        
                WHEN NOT MATCHED THEN                                         
                    INSERT (signature, category, obj_type, plan_id, comp_data,
                              spare1, spare2)                                 
                        VALUES (:7, :8, :9, :10, :11, null, null)


call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse     6523      0.18       0.19          0          0          0           0
Execute   6523      3.15       8.90       1059      34474      17486         452
Fetch     6071      0.22       0.20          0      12142          0        6071
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total    19117      3.55       9.30       1059      46616      17486        6523

Misses in library cache during parse: 0
Optimizer mode: CHOOSE
Parsing user id: SYS   (recursive depth: 2)

Rows     Row Source Operation
-------  ---------------------------------------------------
      0  MERGE  SQLOBJ$DATA (cr=79 pr=3 pw=1 time=16359 us)
   2440   VIEW  (cr=43 pr=0 pw=0 time=15141 us)
   2440    MERGE JOIN OUTER (cr=43 pr=0 pw=0 time=13065 us cost=9 size=303596 card=2138)
      1     TABLE ACCESS FULL DUAL (cr=2 pr=0 pw=0 time=59 us cost=2 size=2 card=1)
   2440     VIEW  (cr=41 pr=0 pw=0 time=7394 us cost=7 size=299320 card=2138)
   2440      FILTER  (cr=41 pr=0 pw=0 time=6050 us)
   2440       INDEX FAST FULL SCAN SQLOBJ$DATA_PKEY (cr=41 pr=0 pw=0 time=3971 us cost=6 size=299320 card=2138)(object id 205)


Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  db file sequential read                       607        0.09          1.96
  direct path read                              450        0.03          0.51
  flashback log file sync                       592        0.01          1.51
  direct path write                             452        0.02          1.02
  latch: cache buffers chains                    72        0.00          0.00
  buffer busy waits                              54        0.00          0.01
  enq: HW - contention                           70        0.04          0.61
  enq: TX - index contention                      8        0.00          0.00
  read by other session                           1        0.01          0.01
********************************************************************************

SQL ID: 44z7snw61qx9x
Plan Hash: 1133963577

*** 2011-03-01 11:38:27.933
MERGE INTO sqlobj$auxdata                        
                               USING dual ON (:1 IS NULL)                     
                                 WHEN MATCHED THEN                            
                                     UPDATE SET description = :2,             
                                                  creator = nvl(:3, creator), 
                                                    origin = :4,              
                                                      version = :5,           
                                                        created = :6,         
                                                          last_modified = :7, 
                                                            last_verified = 
  nvl(:8, last_verified),                                       
  parse_cpu_time = null,                                                      
    optimizer_cost = nvl(:9, optimizer_cost),                                 
      module = nvl(:10, module),                                              
        action = nvl(:11, action),                                            
          priority = nvl(:12, priority),                                      
            optimizer_env = nvl(:13, optimizer_env),                          
              bind_data = nvl(:14, bind_data),                                
                parsing_schema_name = nvl(:15, parsing_schema_name),          
                  executions = nvl(:16, executions),                          
                    elapsed_time = nvl(:17, elapsed_time),                    
                      cpu_time = nvl(:18, cpu_time),                          
                        buffer_gets = nvl(:19, buffer_gets),                  
                          disk_reads = nvl(:20, disk_reads),                  
                            direct_writes = nvl(:21, direct_writes),          
                              rows_processed = nvl(:22, rows_processed),      
                                fetches = nvl(:23, fetches),                  
                                  end_of_fetch_count = nvl(:24, 
  end_of_fetch_count),                            task_id = nvl(:25, task_id),
                                                    task_exec_name = nvl(:26, 
  task_exec_name),                                    task_obj_id = nvl(:27, 
  task_obj_id),                                          task_fnd_id = 
  nvl(:28, task_fnd_id),                                          task_rec_id 
  = nvl(:29, task_rec_id),                                          flags = 0,
                                                                      spare1 =
   null,                                                                
  spare2 = null                                                      WHERE 
  signature = :30                                                             
    AND category = :31                                                        
      AND obj_type = :32                                                      
        AND plan_id = :33                                                     
  WHEN NOT MATCHED THEN                                                       
      INSERT (signature, category, obj_type, plan_id,                         
                description, creator, origin, version,                        
                  created, last_modified, last_verified, parse_cpu_time,      
                    optimizer_cost, module, action, priority,                 
                      optimizer_env, bind_data, parsing_schema_name, 
  executions,                    elapsed_time, cpu_time, buffer_gets, 
  disk_reads,                              direct_writes, rows_processed, 
  fetches,end_of_fetch_count,                    task_id, task_exec_name, 
  task_obj_id, task_fnd_id,                            task_rec_id, flags, 
  spare1, spare2)                                   VALUES (:34, :35, :36, 
  :37,                                                           :38, :39, 
  :40, :41,                                                           :42, 
  :43, null, null,                                                         
  :44, :45, :46, :47,                                                         
    :48, :49, :50, :51,                                                       
      :52, :53, :54, :55,                                                     
        :56, :57, :58, :59,                                                   
          :60, :61, :62, :63,                                                 
            :64

call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.00       0.00          0          0          0           0
Execute      1      0.00       0.00          0        252          2           1
Fetch        0      0.00       0.00          0          0          0           0
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total        2      0.00       0.00          0        252          2           1

Misses in library cache during parse: 0
Optimizer mode: CHOOSE
Parsing user id: SYS   (recursive depth: 2)

Rows     Row Source Operation
-------  ---------------------------------------------------
      0  MERGE  SQLOBJ$AUXDATA (cr=252 pr=0 pw=0 time=4892 us)
   2440   VIEW  (cr=252 pr=0 pw=0 time=7181 us)
   2440    MERGE JOIN OUTER (cr=252 pr=0 pw=0 time=5835 us cost=18 size=784646 card=2138)
      1     TABLE ACCESS FULL DUAL (cr=2 pr=0 pw=0 time=71 us cost=2 size=2 card=1)
   2440     VIEW  (cr=250 pr=0 pw=0 time=4912 us cost=16 size=780370 card=2138)
   2440      FILTER  (cr=250 pr=0 pw=0 time=3808 us)
   2440       TABLE ACCESS FULL SQLOBJ$AUXDATA (cr=250 pr=0 pw=0 time=2953 us cost=20 size=780370 card=2138)

********************************************************************************

SQL ID: bsa0wjtftg3uw
Plan Hash: 2020579421
select file# 
from
 file$ where ts#=:1


call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.00       0.00          0          0          0           0
Execute      1      0.00       0.00          0          0          0           0
Fetch       15      0.00       0.00          0         29          0          14
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total       17      0.00       0.00          0         29          0          14

Misses in library cache during parse: 1
Misses in library cache during execute: 1
Optimizer mode: CHOOSE
Parsing user id: SYS   (recursive depth: 3)

Rows     Row Source Operation
-------  ---------------------------------------------------
     14  TABLE ACCESS BY INDEX ROWID FILE$ (cr=29 pr=0 pw=0 time=88 us cost=1 size=35 card=5)
     14   INDEX RANGE SCAN I_FILE2 (cr=15 pr=0 pw=0 time=151 us cost=1 size=0 card=5)(object id 44)




********************************************************************************

OVERALL TOTALS FOR ALL NON-RECURSIVE STATEMENTS

call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        2      0.01       0.01          0          0          0           0
Execute      2      1.08       1.14          0          0          1           0
Fetch        0      0.00       0.00          0          0          0           0
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total        4      1.09       1.15          0          0          1           0

Misses in library cache during parse: 1

Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  log file sync                                   3        0.06          0.07
  SQL*Net message to client                       6        0.00          0.00
  SQL*Net message from client                     6       27.68         47.53
  reliable message                                1        0.00          0.00
  Disk file operations I/O                        3        0.00          0.00
  Parameter File I/O                              8        0.01          0.02
  SQL*Net break/reset to client                   2        0.00          0.00
  direct path read                             6503        0.75         18.96
  latch: cache buffers chains                    78        0.00          0.00
  buffer busy waits                             103        0.00          0.00
  library cache: mutex X                         17        0.00          0.00


OVERALL TOTALS FOR ALL RECURSIVE STATEMENTS

call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse    39047      1.64       1.70          0          0          1           0
Execute  45549    158.03     342.53      22465    2652285     286877       19521
Fetch    39115      1.12       1.16          1      84889          0       32634
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total   123711    160.80     345.40      22466    2737174     286878       52155

Misses in library cache during parse: 21
Misses in library cache during execute: 17

Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  Disk file operations I/O                       15        0.00          0.00
  db file sequential read                      9457        1.04         49.35
  flashback log file sync                      8420        0.26         26.86
  direct path write                            6504        0.47         37.64
  direct path read                             6495        0.42         16.86
  enq: HW - contention                         1208        0.89         25.03
  latch: cache buffers chains                  1024        0.00          0.04
  buffer busy waits                             941        1.00          6.02
  read by other session                          25        0.03          0.36
  latch: enqueue hash chains                      2        0.00          0.00
  library cache: mutex X                         16        0.00          0.00
  enq: TX - index contention                     65        0.05          0.21
  buffer deadlock                                11        0.00          0.00
  log file switch completion                      5        0.24          0.50
  latch free                                      2        0.00          0.00
  latch: shared pool                              8        0.00          0.00
  latch: object queue header operation            1        0.00          0.00
  latch: cache buffers lru chain                  4        0.00          0.00
  log file switch (checkpoint incomplete)         3        0.14          0.28
  enq: TX - allocate ITL entry                    1        0.00          0.00
  latch: undo global data                         1        0.00          0.00

    4  user  SQL statements in session.
19540  internal SQL statements in session.
19544  SQL statements in session.
********************************************************************************


....

       1  session in tracefile.
       4  user  SQL statements in trace file.
   19540  internal SQL statements in trace file.
   19544  SQL statements in trace file.
      20  unique SQL statements in trace file.
 3288358  lines in trace file.
     394  elapsed seconds in trace file.
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4 Responses to Buggy overhead of SQL Plan Baseline Capture

  1. alan Rosenthal says:

    Hi,

    Excellent analysis. We just discovered this bug after pulling our hair out for the last 6 months.

    Question – is it enough to just turn of the optimizer_capture_sql_plan_baselines=false parameter to make this problem go away?

    There is an opatch (11719151) that seems to fix this. But it is too close to quarter end for us to apply patches to production. We could do it next month.

    Thanks,

    Alan

    • Dom Brooks says:

      Hi Alan,

      Until I patched this, I ran with both parameters set to FALSE and any pre-existing baselines deleted and performance was ok.

      Once the patch (11719151) was approved internally and applied, it fixed the problem

      Hope this helps.

      Cheers,
      Dominic

  2. alan Rosenthal says:

    Hi Dominic,

    Last November we upgraded our Oracle Apps 11.5.10.2 system from RDBMS 9.2.0.8 to 11.2.0.2. It has been something of a nightmare. Granted the fault was ours. We didn’t test the upgrade enough. Several other emergencies slammed us at the same time and database testing fell through the cracks. My bad. But here is a quick summary of what happened:

    In a nutshell – the peformance of the entire system was terrible. Everything was sluggish. It seemed to be systemic rather than isolated to any single process or set of processes.

    The first problem we noticed involved reading the data dictionary. When we started up development tools like Sql Navigator or Toad they tried to pre-load parts of the schema. This took minutes to open the tools. Also, searching for objects within the database seemed to take forever. We found a bug in the ALL_SYNONYMS view. We ran the fix in note: Selects Against ALL_SYNONYMS Very Slow in 11.2.0.1. and 11.2.0.2. [ID 1242844.1] and this seemed to help.

    But the system was still slow.

    Next, having nothing to do with overall performance, we found an optimizer bug that was causing certain where clauses with OR’s and repeating column names to return incorrect (generally nothing) results. This was breaking a couple forms that couldn’t query. We fixed this with bug 9776940 and a hidden parameter “_projection_pushdown” = FALSE.

    But the system was still slow.

    Next, we noticed that the server was doing an incredible amount of virtual memory page-in’s. At the rate of 4000 to 6000 pages per second. There was no apparent reason for this since the servers seemed to have plenty of free RAM and swap space. After much looking by several people we discovered that the ASO_ORDER_FEEDBACK_T queue had grown very large and the new 11g database was doing full table scans on it at an alarming pace – basically continues FTS again and again and again. Since they were full table scans it was causing the table to be read in from the database everytime and as it was read into the SGA it was also being read into the swap space. We cleaned up the table with How to Purge the ASO_ORDER_FEEDBACK_T Table In Minimum time Using Asoqueue Script ? (Doc ID 740305.1). and the page-in rate dropped to a very small number.

    This greatly improved the situation. But the system was still slow.

    Then we started investigating one process – Journal Import. On our old 9i database a particular test ran in about 2 minutes. On the new 11g database it took 50 minutes. Oracle support said that nothing was wrong. We disagreed. After lots of back and forth, I was looking at the trace file and noticed 3 different MERGE INTO SQLOBJ$DATA and SQLOBJ$AUXDATA. I didn’t know what these tables were. But a quick google search found that they were part of the SQL Plan Management Capture process. When I added up the times for these three MERGE INTO’s it came to 46 minutes. Adding that to the 2 minutes that the process should have taken gave me almost exactly the actual run time of 50 minutes. Once I found this it was trivial to find out that SQL Plan Capture has a bug in it – Bug 11719151: MERGE STATEMENT USED WHEN SPM CAPTURE CAUSING PERFORMANCE ISSUE . We turned off capture by setting optimizer_capture_sql_plan_baselines=FALSE and performance dramatically improved. We are working on the opatch to repair this problem but it will have to wait until after quarter end processing.

    The moral of the story – there is a good reason why they say to test your upgrades before going into production :)

    Cheers,
    Alan

  3. Pingback: Outline, SQL profile and SQL Plan Management(SPM) « Oracle Explorer: Standing on the shoulders of giants

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