High wio on New Hitachi SAN Storage of DB Server

From: VIVEK_SHARMA <VIVEK_SHARMA_at_infosys.com>
Date: Sat, 12 Nov 2005 00:26:29 +0530
Message-ID: <BBD944BCAC3AB4499DFBAFB1D8AF3020290C7E@BLRKECMSG11.ad.infosys.com>

Folks,

While doing Application Testing of Hybrid Trans (OLTP mostly though) by 200 users (approx) on a NEWLY configured HITACHI SAN Storage, on DB Server (of AIX) High wait for IO i.e. wio = 70 % till 1400 Hours is observed.

NOTE - wio reduced to about 10 % gradually from 1400 Hours to 2000 Hours.

Average sar Output from morning to 1400 Hours:-

13:38:00    %usr    %sys    %wio   %idle
13:43:00       6       5      67      22
13:48:00      10       6      74      10
13:53:00      10       5      66      19
13:58:00       7       5      61      27
14:03:00       5       5      67      22
14:08:00       7       5      74      15
14:13:00       9       6      69      15

CONFIG

DB Server = 7 CPUs
OS AIX 5.2
Oracle 8.1.7
Hitachi Storage for DB Server = 40 underlying Disks Hardware Raid
Init.ora disk_asynch_io = FALSE (When disk_asynch_io is set TRUE there is extreme performance degradation with AIX 5.2 [seems a bug])

Comments by IBM

The average number of process waiting for IO to complete is 12. This indicates that these processes are waiting for the IO to complete. This is the reason why we are seeing an average iowait of 70%.

The seek rate is 95.72% on the hdsdb9960lv LV's indicates a high degree of random IO, usually caused by the application or a high degree of disk fragmentation.

STATSPACK report (will provide any other sections as needed)

DB Name DB Id Instance Inst Num Release OPS Host ------------ ----------- ------------ -------- ----------- ---

ABNPROD 34298189 abnprod 1 8.1.7.4.0 NO findb

                Snap Id     Snap Time      Sessions
                ------- ------------------ --------
 Begin Snap:          5 15-Oct-05 13:00:55      352
   End Snap:          6 15-Oct-05 14:00:37      352
    Elapsed:                  59.70 (mins)

Cache Sizes

           db_block_buffers:     215000          log_buffer:   18874368
              db_block_size:       8192    shared_pool_size:  754288000

Load Profile
~~~~~~~~~~~~                            Per Second       Per Transaction
                                   ---------------       ---------------
                  Redo size:            298,013.21                837.31
              Logical reads:             55,540.47                156.05
              Block changes:              2,296.74                  6.45
             Physical reads:              3,109.99                  8.74
            Physical writes:                399.33                  1.12
                 User calls:              2,657.16                  7.47
                     Parses:                 64.98                  0.18
                Hard parses:                  5.44                  0.02
                      Sorts:                 75.56                  0.21
                     Logons:                  0.75                  0.00
                   Executes:              1,783.45                  5.01
               Transactions:                355.92

  % Blocks changed per Read:    4.14    Recursive Call %:   15.67
 Rollback per transaction %:   94.71       Rows per Sort:   10.87


Top 5 Wait Events
~~~~~~~~~~~~~~~~~                                             Wait     %
Total
Event                                               Waits  Time (cs)

Wt Time

-------------------------------------------- ------------ ------------
-------
db file sequential read                         6,230,712    1,640,351
43.84
log file sync                                   1,087,475    1,286,467
34.38
db file scattered read                            351,411      416,508
11.13
log file parallel write                           706,201      288,168
7.70
buffer busy waits                                 334,943       69,830
1.87
          -------------------------------------------------------------

Qs How might this issue be approached?
Qs Are there any special O.S. parameters that might be set?

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Received on Fri Nov 11 2005 - 13:01:00 CST