Overall I/O Query

I hacked together a query today that shows the overall I/O performance that a database is experiencing.

The output looks like this:

End snapshot time   number of IOs ave IO time (ms) ave IO size (bytes)
------------------- ------------- ---------------- -------------------
2015-06-15 15:00:59        359254               20              711636
2015-06-15 16:00:59        805884               16              793033
2015-06-15 17:00:13        516576               13              472478
2015-06-15 18:00:27        471098                6              123565
2015-06-15 19:00:41        201820                9              294858
2015-06-15 20:00:55        117887                5              158778
2015-06-15 21:00:09         85629                1               79129
2015-06-15 22:00:23        226617                2               10744
2015-06-15 23:00:40        399745               10              185236
2015-06-16 00:00:54       1522650                0               43099
2015-06-16 01:00:08       2142484                0               19729
2015-06-16 02:00:21        931349                0                9270

I’ve combined reads and writes and focused on three metrics – number of IOs, average IO time in milliseconds, and average IO size in bytes.  I think it is a helpful way to compare the way two systems perform.  Here is another, better, system’s output:

End snapshot time   number of IOs ave IO time (ms) ave IO size (bytes)
------------------- ------------- ---------------- -------------------
2015-06-15 15:00:25        331931                1              223025
2015-06-15 16:00:40        657571                2               36152
2015-06-15 17:00:56       1066818                1               24599
2015-06-15 18:00:11        107364                1              125390
2015-06-15 19:00:26         38565                1               11023
2015-06-15 20:00:41         42204                2              100026
2015-06-15 21:00:56         42084                1               64439
2015-06-15 22:00:15       3247633                3              334956
2015-06-15 23:00:32       3267219                0               49896
2015-06-16 00:00:50       4723396                0               32004
2015-06-16 01:00:06       2367526                1               18472
2015-06-16 02:00:21       1988211                0                8818

Here is the query:

select 
to_char(sn.END_INTERVAL_TIME,'YYYY-MM-DD HH24:MI:SS') "End snapshot time",
sum(after.PHYRDS+after.PHYWRTS-before.PHYWRTS-before.PHYRDS) "number of IOs",
trunc(10*sum(after.READTIM+after.WRITETIM-before.WRITETIM-before.READTIM)/
sum(1+after.PHYRDS+after.PHYWRTS-before.PHYWRTS-before.PHYRDS)) "ave IO time (ms)",
trunc((select value from v$parameter where name='db_block_size')*
sum(after.PHYBLKRD+after.PHYBLKWRT-before.PHYBLKRD-before.PHYBLKWRT)/
sum(1+after.PHYRDS+after.PHYWRTS-before.PHYWRTS-before.PHYRDS)) "ave IO size (bytes)"
from DBA_HIST_FILESTATXS before, DBA_HIST_FILESTATXS after,DBA_HIST_SNAPSHOT sn
where 
after.file#=before.file# and
after.snap_id=before.snap_id+1 and
before.instance_number=after.instance_number and
after.snap_id=sn.snap_id and
after.instance_number=sn.instance_number
group by to_char(sn.END_INTERVAL_TIME,'YYYY-MM-DD HH24:MI:SS')
order by to_char(sn.END_INTERVAL_TIME,'YYYY-MM-DD HH24:MI:SS');

I hope this is helpful.

– Bobby

About Bobby

I live in Chandler, Arizona with my wife and three daughters. I work for US Foods, the second largest food distribution company in the United States. I've been working as an Oracle database administrator and PeopleSoft administrator since 1994. I'm very interested in Oracle performance tuning.
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2 Responses to Overall I/O Query

  1. Thank you Bobby, good scripts and your blog is also very useful for other DBAs like me..I am your frequent reader…waiting for new stuffs and experience notes

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