Skip to Main Content

Breadcrumb

Question and Answer

Connor McDonald

Thanks for the question, Sudhakar.

Asked: October 24, 2017 - 2:33 am UTC

Last updated: October 24, 2017 - 3:29 am UTC

Version: 11.2.0.3

Viewed 10K+ times! This question is

You Asked

Dear Tom,

My team is trying to write a query for measuring Disk I/O latency in milli seconds.
my team is looking to query v$system_event, but this view has accumulated values of metrics from the startup time of the instance.
Please advise which tables would provide accurate metrics for disk I/O latency ?

Thanks
Sud

and Connor said...

v$event_histogram would be a good place to start. You get counts per "latency range"

SQL> select * from v$event_histogram
  2  where event like 'db file%'
  3  order by 2,3;

    EVENT# EVENT                                                            WAIT_TIME_MILLI WAIT_COUNT
---------- ---------------------------------------------------------------- --------------- ----------
       ...
       169 db file parallel read                                                          1        134
       169 db file parallel read                                                          2          4
       167 db file parallel write                                                         1      69623
       167 db file parallel write                                                         2        943
       167 db file parallel write                                                         4        143
       167 db file parallel write                                                         8         35
       167 db file parallel write                                                        16       2225
       167 db file parallel write                                                        32         26
       167 db file parallel write                                                        64         10
       167 db file parallel write                                                       128          9
       167 db file parallel write                                                       256          4
       165 db file scattered read                                                         1      10596
       165 db file scattered read                                                         2        406
       165 db file scattered read                                                         4         20
       165 db file scattered read                                                         8          1
       165 db file scattered read                                                        16         23
       164 db file sequential read                                                        1      50567
       164 db file sequential read                                                        2        275
       164 db file sequential read                                                        4         77
       164 db file sequential read                                                        8         28
       164 db file sequential read                                                       16         85
       164 db file sequential read                                                       32         13
       164 db file sequential read                                                       64          2
       164 db file sequential read                                                      128          3
       164 db file sequential read                                                      256          2
       ...




Is this answer out of date? If it is, please let us know via a Comment

More to Explore

Performance

Get all the information about database performance in the Database Performance guide.