Thanks for the question, yulin.

Asked: June 30, 2021 - 1:07 pm UTC

Last updated: July 19, 2021 - 5:47 am UTC

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A reader, July banner">

g=the-abnormal-rman-backup-with-lots-of-regularly-periodically-zero-io-values" class="t-Button t-Button--noLabel t-Button--noUI t-Button--icon t-Button--small t-Button--pillStart" title="Bookmark" aria-label="Bookmark"> fa fa-bookmark" aria-hidden="true"> class="t-Button t-Button--noLabel t-Button--noUI t-Button--icon t-Button--small t-Button--pillEnd scroll-to-bottom" title="Bottom" aria-label="Bottom"> fa fa-long-arrow-down" aria-hidden="true"> of the event_name of "RMAN backup & recovery I/O", i.e. fetch the data from disk to PGA ？
2) How to explain the bulk of "RMAN backup & recovery I/O" and "TIME_WAITED" with intermittently zero I/O value ？
3) Why there would a non-zero value of "TIME_WAITED" whereas the other corresponding I/O values were all zero ？
4) Why the event of "MML write backup piece" would also have a non-zero "RD_IO_*" versus the zero values of "WR_IO_*" ？

SAMPLE_TIME                  EVENT                               RD_IO_REQ WR_IO_REQ   RD_IO_BYTES   WR_IO_BYTES TIME_WAITED ----------------------------------- --------- --------- ------------- ------------- ----------- RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0    28100012 Backup: MML write backup piece             32         0      16777216             0        2211 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0    28011851 RMAN backup & recovery I/O                 32         0      16777216             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0    27666316 Backup: MML write backup piece             16         0       8388608             0        8319 RMAN backup & recovery I/O                 16         0       8388608             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0    27968485 RMAN backup & recovery I/O                 32         0      16777216             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0    25492225 Backup: MML write backup piece             16         0       8388608             0        6384 RMAN backup & recovery I/O                 16         0       8388608             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0    27961726 RMAN backup & recovery I/O                 32         0      16777216             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 RMAN backup & recovery I/O                  0         0             0             0           0 thing, but an active session history thing.

Lets say I leave home to drive to the shop at 9am, and its going to take me (about) 13 mins.  If I do it like this:

9:01am, time taken = 1min
9:02am, time taken = 2min
9:03am, time taken = 3min
9:04am, time taken = 4min
....
9:13am, time taken = 13mins ARRIVAL 

then if I add up the times, it looks like the TOTAL time was 98mins...which it obviously wasn't.  So we record it like like this:

9:01am, time taken = 0min (in transit)
9:02am, time taken = 0min(in transit)
9:03am, time taken = 0min (in transit)
9:04am, time taken = 0min (in transit)
....
9:13am, time taken = 13mins ARRIVAL 

which is what you see in active session history. An event that is still in progress records 0.

"RMAN backup & recovery I/O" is anything that relates to RMAN doing I/O to disk (reading or writing).

In terms of RD vs WR, a backup could possibly involve writes *and* reads depending on the type of backup and/or the RMAN operations being performed.

Some of those waits look mighty long though... 
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name="9545214700346216788"> some RMAN I/O statistic in the ASH 07, 2021 - 12:46 pm UTC

So 。。。
a) What the differece about all the corresponding zero I/O values between the zero and non-zero values of "TIME_WAITED"
b) Still not understand why "MML write backup piece" would also have a non-zero "RD_IO" versus the zero values of "WR_IO"

July 08, 2021 - 3:49 am UTC

Time wait is in usecs, so 28100012 is 28 seconds. I suspect that is tape latency or a consequence of the tape driver, ie, "give me a whole lot of data and I'll get back you later"

Can we see your full RMAN script

The doubt about some RMAN I/O statistic in the ASH

A reader, July 08, 2021 - 12:51 pm UTC

I don't think that it might have sth to do with the RMAN script
itself 。。。！

RUN {
# Backup Database
ALLOCATE CHANNEL ch00 TYPE 'SBT_TAPE' ;
ALLOCATE CHANNEL ch01 TYPE 'SBT_TAPE' ;
ALLOCATE CHANNEL ch02 TYPE 'SBT_TAPE' ;
BACKUP
    $BACKUP_TYPE
    FILESPERSET 10
    FORMAT 'bk_%s_%p_%t'
    DATABASE;
    sql 'alter system archive log current';
RELEASE CHANNEL ch00;
RELEASE CHANNEL ch01;
RELEASE CHANNEL ch02;
# backup all archive logs
ALLOCATE CHANNEL ch00 TYPE 'SBT_TAPE' ;
ALLOCATE CHANNEL ch01 TYPE 'SBT_TAPE' ;
BACKUP
   filesperset 40
   FORMAT 'al_%s_%p_%t'
   ARCHIVELOG ALL;
#   DELETE NOPROMPT ARCHIVELOG ALL BACKED UP 1 TIMES TO DEVICE TYPE SBT COMPLETED BEFORE 'SYSDATE-7';
RELEASE CHANNEL ch00;
RELEASE CHANNEL ch01;
}

July 09, 2021 - 4:08 am UTC

Try a "fake tape" backup and see what is observed, eg

RMAN> run {
 allocate channel t1 type 'SBT' PARMS 'SBT_LIBRARY=oracle.disksbt,ENV=(BACKUP_DIR=/tmp)';
 backup tablespace sysaux;
}

If you don't see any waits, then it is going to be an issue with RMAN's interaction with the tape library software.

It should not be the tape issue

A reader, July 12, 2021 - 10:05 am UTC

SAMPLE_TIME                 EVENT                               RD_IO_REQ WR_IO_REQ   RD_IO_BYTES   WR_IO_BYTES TIME_WAITED
--------------------------- ----------------------------------- --------- --------- ------------- ------------- -----------
11-JUL-21 05.56.21.370 AM   RMAN backup & recovery I/O                 70         0      36700160             0      306670
11-JUL-21 05.56.22.371 AM   RMAN backup & recovery I/O                 67         0      35127296             0      328290
11-JUL-21 05.56.23.371 AM   RMAN backup & recovery I/O                 75         0      39321600             0      348116
11-JUL-21 05.56.24.372 AM   Backup: MML write backup piece             76         0      39845888             0        4081
11-JUL-21 05.56.25.372 AM   Backup: MML write backup piece             86         0      45088768             0        1947
11-JUL-21 05.56.26.373 AM   RMAN backup & recovery I/O                 73         0      38273024             0      302455
11-JUL-21 05.56.27.373 AM   RMAN backup & recovery I/O                 71         0      37224448             0      285033
11-JUL-21 05.56.28.374 AM   Backup: MML write backup piece             64         0      33554432             0        2041
11-JUL-21 05.56.29.375 AM   RMAN backup & recovery I/O                 82         0      42991616             0      348326
11-JUL-21 05.56.30.375 AM   RMAN backup & recovery I/O                 68         0      35651584             0      329618
11-JUL-21 05.56.31.386 AM   Backup: MML write backup piece             74         0      38797312             0        2964
11-JUL-21 05.56.32.387 AM   Backup: MML write backup piece             72         0      37748736             0       14208
11-JUL-21 05.56.33.387 AM   RMAN backup & recovery I/O                 63         0      33030144             0      378813
11-JUL-21 05.56.34.388 AM   Backup: MML write backup piece             88         0      46137344             0        2366
11-JUL-21 05.56.35.389 AM   Backup: MML write backup piece             72         0      37748736             0        1788
11-JUL-21 05.56.36.389 AM   RMAN backup & recovery I/O                 69         0      36175872             0      300416
11-JUL-21 05.56.37.390 AM   RMAN backup & recovery I/O                 69         0      36175872             0      273193
11-JUL-21 05.56.38.390 AM   RMAN backup & recovery I/O                 75         0      39321600             0      266829
11-JUL-21 05.56.39.391 AM   RMAN backup & recovery I/O                 62         0      32505856             0      332185
11-JUL-21 05.56.40.392 AM   Backup: MML write backup piece             82         0      42991616             0        1936
11-JUL-21 05.56.41.392 AM   Backup: MML write backup piece             85         0      44564480             0       14587
11-JUL-21 05.56.42.393 AM   Backup: MML write backup piece             77         0      40370176             0        2753
11-JUL-21 05.56.43.393 AM   Backup: MML write backup piece             84         0      44040192             0        4466
11-JUL-21 05.56.44.394 AM   Backup: MML write backup piece             72         0      37748736             0        4441
11-JUL-21 05.56.45.395 AM   Backup: MML write backup piece             88         0      46137344             0        4569
11-JUL-21 05.56.46.396 AM   RMAN backup & recovery I/O                 74         0      38797312             0      270967
11-JUL-21 05.56.47.396 AM   RMAN backup & recovery I/O                 70         0      36700160             0      277731
11-JUL-21 05.56.48.397 AM   Backup: MML write backup piece             98         0      51380224             0       12554
11-JUL-21 05.56.49.398 AM   RMAN backup & recovery I/O                 69         0      36175872             0      308259
11-JUL-21 05.56.50.398 AM   Backup: MML write backup piece             79         0      41418752             0        1688
11-JUL-21 05.56.51.399 AM   Backup: MML write backup piece             94         0      49283072             0        2185
11-JUL-21 05.56.52.399 AM   Backup: MML write backup piece             82         0      42991616             0        1911
11-JUL-21 05.56.53.400 AM   RMAN backup & recovery I/O                 82         0      42991616             0      316635
11-JUL-21 05.56.54.400 AM   Backup: MML write backup piece             68         0      35651584             0        3080
11-JUL-21 05.56.55.401 AM   RMAN backup & recovery I/O                 86         0      45088768             0      262187
11-JUL-21 05.56.56.402 AM   Backup: MML write backup piece             78         0      40894464             0        4327
11-JUL-21 05.56.57.402 AM   Backup: MML write backup piece             80         0      41943040             0        2135
11-JUL-21 05.56.58.403 AM   RMAN backup & recovery I/O                 92         0      48234496             0      282213
11-JUL-21 05.56.59.403 AM   RMAN backup & recovery I/O                 69         0      36175872             0      290679
11-JUL-21 05.57.00.404 AM   RMAN backup & recovery I/O                 71         0      37224448             0      273410
11-JUL-21 05.57.01.405 AM   RMAN backup & recovery I/O                 84         0      44040192             0      307111
11-JUL-21 05.57.02.406 AM   Backup: MML write backup piece             98         0      51380224             0        2153
11-JUL-21 05.57.03.406 AM   RMAN backup & recovery I/O                 74         0      38797312             0      333547
11-JUL-21 05.57.04.407 AM   RMAN backup & recovery I/O                 72         0      37748736             0      275967
11-JUL-21 05.57.05.407 AM   Backup: MML write backup piece             96         0      50331648             0        2167
11-JUL-21 05.57.06.408 AM   RMAN backup & recovery I/O                 77         0      40370176             0      290807
11-JUL-21 05.57.07.409 AM   RMAN backup & recovery I/O                 73         0      38273024             0      284899
11-JUL-21 05.57.08.409 AM   Backup: MML write backup piece             96         0      50331648             0        1985
11-JUL-21 05.57.09.410 AM   RMAN backup & recovery I/O                 60         0      31457280             0      343500
11-JUL-21 05.57.10.410 AM   Backup: MML write backup piece             80         0      41943040             0        1775
11-JUL-21 05.57.11.411 AM   Backup: MML write backup piece             94         0      49283072             0        1948

July 13, 2021 - 3:31 am UTC

o....k....

The doubt about some RMAN I/O statistic in the ASH

A reader, July 16, 2021 - 2:36 am UTC

Thus, it seems that what you have answered recently do not have sth to do with my following questions。。。。
a) What the differece about all the corresponding zero I/O values between the zero and non-zero values of "TIME_WAITED"
b) Still not understand why "MML write backup piece" would also have a non-zero "RD_IO" versus the zero values of "WR_IO"

July 19, 2021 - 5:47 am UTC

You posted the results of a query with no context, no description, no ... anything.

So we really couldn't do a lot....

Item (a) we explained earlier
Item (b) we asked about using the psuedo-tape driver, and well...maybe you did, maybe you didn't...we can't tell from what you pasted.

The doubt about some RMAN I/O statistic in the ASH

A reader, July 20, 2021 - 2:46 am UTC

But I do want to firstly understand these I/O statistical indicators in practical significances 。。。

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A reader, July banner">

The doubt about some RMAN I/O statistic in the ASH

It should not be the tape issue

The doubt about some RMAN I/O statistic in the ASH

The doubt about some RMAN I/O statistic in the ASH

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The abnormal RMAN backup with lots of regularly & periodically zero I/O values

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The doubt about some RMAN I/O statistic in the ASH

It should not be the tape issue

The doubt about some RMAN I/O statistic in the ASH

The doubt about some RMAN I/O statistic in the ASH

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