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Oracle 11.2 new v$ iostat views

Oracle Database Tips by Burleson Consulting

February 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_no

File identification number

filetype_id

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

filetype_name

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).

small_read_megabytes

Number of single block megabytes read

small_write_megabytes

Number of single block megabytes written

large_read_megabytes

Number of multiblock megabytes read

large_write_megabytes

Number of multiblock megabytes written

small_read_reqs

Number of single block read requests

small_write_reqs

Number of single block write requests

small_sync_read_reqs

Number of synchronous single block read requests

large_read_reqs

Number of multiblock read requests

large_write_reqs

Number of multiblock write requests

small_read_servicetime

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

small_write_servicetime

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

small_sync_read_latency

Latency for single block synchronous reads (in milliseconds)

large_read_servicetime

Total service time (in milliseconds) for multiblock read requests

large_write_servicetime

Total service time (in milliseconds) for multiblock write requests

asynch_io

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

retries_on_error

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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