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Don Burleson Blog 







Oracle 11.2 new v$ iostat views

Oracle Database Tips by Donald BurlesonFebruary 11, 2015

Oracle release 11.2 has introduced new iostat views that show the resource usage against the physical disk spindles.

These are very important new AWR tables because it allows Oracle to look outside of the database and get statistics directly on disk service rimes.

v$iostat_consumer_group:  See v$iostat consumer group

v$iostat_file:  This has valuable file I/O statistics.  What is missing is the all-important disk enqueues which would indicate disk contention for a device.  However, this could be inferred from read service time, provided that the two AWR snapshots are less then 60 seconds apart and the file is not striped across multiple disks:



File identification number


Type of file (for example, log file, data file, and so on)


Name of the file, in the case of a data file or temp file. For all other files, a corresponding string to be displayed (for example, ARCHIVELOG).


Number of single block megabytes read


Number of single block megabytes written


Number of multiblock megabytes read


Number of multiblock megabytes written


Number of single block read requests


Number of single block write requests


Number of synchronous single block read requests


Number of multiblock read requests


Number of multiblock write requests


Total service time (in milliseconds) for single block read requests


Total service time (in milliseconds) for single block write requests


Latency for single block synchronous reads (in milliseconds)


Total service time (in milliseconds) for multiblock read requests


Total service time (in milliseconds) for multiblock write requests


Indicates whether asynchronous I/O is available for the file (ASYNC_ON) or not (ASYNC_OFF)


Number of read retries on error

v$iostat_function & v$iostat_function_detail:  This table marks what processes are writing to each disk spindle.  Interesting, but not too helpful in tuning: 

RMAN, DBWR, LGWR, ARCH, XDB, Streams, AQ, Data Pump, Recovery Buffer Cache Reads, Direct Reads, Direct Writes ,Smart Scan, Archive Manager

See v$iostat function

v$iofunctionmetrics:  This table contains avg wait_time, an indicator of a "busy" disk with read enqueues that may cause a database to become I/O-bound.

See v$iofunctionmetrics tips

v$iostat_function tips

v$iostat_network:  This view shows I/O wait times on network traffic, similar to SQL*Net roundtrip metrics.  See v$iostat_network

We also see corresponding DBA_HIST AWR tables for iostat information:

dba_hist_iostat_detail:  See dba_hist_iostat_detail tips

dba_hist_iostat_filetype:  See dba_hist_iostat_filetype tips

dba_hist_iostat_filetype_name:  See dba_hist_iostat_filetype_name tips

dba_hist_iostat_function:  See dba_hist_iostat_function tips

dba_hist_iostat_function_name:  See
dba_hist_iostat_function_name tips


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