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Question and Answer

Connor McDonald

Thanks for the question, A Reader.

Asked: August 24, 2016 - 9:25 am UTC

Last updated: August 29, 2016 - 12:18 pm UTC

Version: 10.2.0.5

Viewed 1000+ times

You Asked

Hi team

We have database showing "Av Rd(ms)" in File IO Stats section of the AWR as high as 500 msec.

asvc_t ( SERVICE time) value of iostats data for the mount point is well within the acceptable 20 msec.

1) could you please share the sql ( I tried little hunting but could not get it) to fetch the "File IO Stats " data from AWR hist tables ?
2) what could be potential issue here - we use NFS mount. I think asvc_t cannot be directly compared with "Av Rd(ms)"

thanks

and Connor said...

V$FILESTAT has some averages since the instance started..


SQL> desc v$filestat
 Name                                                  Null?    Type
 ----------------------------------------------------- -------- -----------
 FILE#                                                          NUMBER
 PHYRDS                                                         NUMBER
 PHYWRTS                                                        NUMBER
 PHYBLKRD                                                       NUMBER
 OPTIMIZED_PHYBLKRD                                             NUMBER
 PHYBLKWRT                                                      NUMBER
 SINGLEBLKRDS                                                   NUMBER
 READTIM                                                        NUMBER
 WRITETIM                                                       NUMBER
 SINGLEBLKRDTIM                                                 NUMBER
 AVGIOTIM                                                       NUMBER
 LSTIOTIM                                                       NUMBER
 MINIOTIM                                                       NUMBER
 MAXIORTM                                                       NUMBER
 MAXIOWTM                                                       NUMBER
 CON_ID                                                         NUMBER


But if you are licensed for ASH, I would sample V$ACTIVE_SESSION_HISTORY for the TIME_WAITED column for the I/O related events. That way you can get some sampled data.

Also, check out V$EVENT_HISTOGRAM for a distribution of the wait times

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Comments

A reader, August 29, 2016 - 8:56 am UTC

But I could't get data from "V$ACTIVE_SESSION_HISTORY" .
so what's another way to seeing performance related database statistics.
Connor McDonald
August 29, 2016 - 12:18 pm UTC

"couldnt" ? Due to licensing ? or something else ?

Check out V$EVENT_HISTOGRAM, deltas in DBA_HIST_FILESTATXS, and consider doing some session tracing.
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