Hi Everyone
I need help resolving a problem with
buffer busy waits in for a lob segment using securefiles for storage.
During the load the application inserts a record into a table with the lob segment and update the record after, populating lob data. The block size on the table space holding the lob is 8 kb and the chunk size on the lob segment is set to 8kb. The average size of the lob record is 6 kb and the minimum size is 4.03 KB. The problem occurs only when running a job with a big number of relatively small inserts (4.03 Kb) in to the lob column . The table definition allow in-row storage and the ptcfree set to 10%. The same jobs runs without problem when using basicfiles storage for the lob column.
According to [oracle white paper |http://www.oracle.com/technetwork/database/options/compression/overview/securefiles-131281.pdf] securefiles have a number of performance enhancements. I was particular interested to test Write Gather Cache as our application does a lot of relatively small inserts into a lob segment.
Below is a fragment from the AWR report. It looks like all buffer busy waits belong to a free list class. The lob segment is located in an ASSM tablespace and I cannot increase freelists.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production
With the Partitioning option
Host Name Platform CPUs Cores Sockets Memory(GB)
---------------- -------------------------------- ---- ----- ------- ----------
DB5 Microsoft Windows x86 64-bit 8 2 31.99
Snap Id Snap Time Sessions Curs/Sess
--------- ------------------- -------- ---------
Begin Snap: 1259 01-Apr-11 14:40:45 135 5.5
End Snap: 1260 01-Apr-11 15:08:59 155 12.0
Elapsed: 28.25 (mins)
DB Time: 281.55 (mins)
Cache Sizes Begin End
~~~~~~~~~~~ ---------- ----------
Buffer Cache: 2,496M 2,832M Std Block Size: 8K
Shared Pool Size: 1,488M 1,488M Log Buffer: 11,888K
Load Profile Per Second Per Transaction Per Exec Per Call
~~~~~~~~~~~~ --------------- --------------- ---------- ----------
DB Time(s): 10.0 0.1 0.01 0.00
DB CPU(s): 2.8 0.0 0.00 0.00
Redo size: 1,429,862.3 9,390.5
Logical reads: 472,459.0 3,102.8
Block changes: 9,849.7 64.7
Physical reads: 61.1 0.4
Physical writes: 98.6 0.7
User calls: 2,718.8 17.9
Parses: 669.8 4.4
Hard parses: 2.2 0.0
W/A MB processed: 1.1 0.0
Logons: 0.1 0.0
Executes: 1,461.0 9.6
Rollbacks: 0.0 0.0
Transactions: 152.3
Top 5 Timed Foreground Events
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Avg
wait % DB
Event Waits Time(s) (ms) time Wait Class
------------------------------ ------------ ----------- ------ ------ ----------
buffer busy waits 1,002,549 8,951 9 53.0 Concurrenc
DB CPU 4,724 28.0
latch: cache buffers chains 11,927,297 1,396 0 8.3 Concurrenc
direct path read 121,767 863 7 5.1 User I/O
enq: DW - contention 209,278 627 3 3.7 Other
?Host CPU (CPUs: 8 Cores: 2 Sockets: )
~~~~~~~~ Load Average
Begin End %User %System %WIO %Idle
--------- --------- --------- --------- --------- ---------
38.7 3.5 57.9
Instance CPU
~~~~~~~~~~~~
% of total CPU for Instance: 40.1
% of busy CPU for Instance: 95.2
%DB time waiting for CPU - Resource Mgr: 0.0
Memory Statistics
~~~~~~~~~~~~~~~~~ Begin End
Host Mem (MB): 32,762.6 32,762.6
SGA use (MB): 4,656.0 4,992.0
PGA use (MB): 318.4 413.5
% Host Mem used for SGA+PGA: 15.18 16.50
.....................
Avg
%Time Total Wait wait Waits % DB
Event Waits -outs Time (s) (ms) /txn time
-------------------------- ------------ ----- ---------- ------- -------- ------
buffer busy waits 1,002,549 0 8,951 9 3.9 53.0
latch: cache buffers chain 11,927,297 0 1,396 0 46.2 8.3
direct path read 121,767 0 863 7 0.5 5.1
enq: DW - contention 209,278 0 627 3 0.8 3.7
log file sync 288,785 0 118 0 1.1 .7
SQL*Net more data from cli 1,176,770 0 103 0 4.6 .6
Buffer Wait Statistics DB/Inst: ORA11G/ora11g Snaps: 1259-1260
-> ordered by wait time desc, waits desc
Class Waits Total Wait Time (s) Avg Time (ms)
------------------ ----------- ------------------- --------------
free list 818,606 8,780 11
undo header 512,358 141 0
2nd level bmb 105,816 29 0
.....
-> Total Logical Reads: 800,688,490
-> Captured Segments account for 19.8% of Total
Tablespace Subobject Obj. Logical
Owner Name Object Name Name Type Reads %Total
---------- ---------- -------------------- ---------- ----- ------------ -------
EAG50NSJ EAG50NSJ SYS_LOB0000082335C00 LOB 127,182,208 15.88
SYS SYSTEM TS$ TABLE 7,641,808 .95
..
-------------------------------------------------------------
Segments by Physical Reads DB/Inst: ORA11G/ora11g Snaps: 1259-1260
-> Total Physical Reads: 103,481
-> Captured Segments account for 224.4% of Total
Tablespace Subobject Obj. Physical
Owner Name Object Name Name Type Reads %Total
---------- ---------- -------------------- ---------- ----- ------------ -------
EAG50NSJ EAG50NSJ SYS_LOB0000082335C00 LOB 218,858 211.50
....
Best regards
Yuri Kogun