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Don Burleson Blog 







v$osstat tips 

Oracle Database Tips by Donald BurlesonJanuary 1, 2015

Question:  I use your STATSPACK extension table for vmstat (stats$vmstat) and I have been quite happy with my IS stats.  I now understand that Oracle offers a view with limited OS data, called v$osstat.  Is v$osstat better than a custom OS statistics collection?

Answer:  Traditionally, Oracle ran in a vacuum, and you had to go "outside" of Oracle to measure CPU, RAM, Network and disk spindle I/O bottlenecks.  However, Oracle has now advanced and an instance samples its external environment placing OS data into v$osstat, dba_hist_system_event

The v$osstat is created by querying the gv$osstat view, slicing-off data for each specific instance on the server:

   inst_id = userenv('instance')

Oracle has several views that collect OS information, namely v$osstat, stats$osstat, stats$osstatname and dba_hist_osstat.

Still, many DBAs will write custom scripts to gather OS statistics, collecting from OS tools such as vmstat and placing the data into STATSPACK extension tables for trend analysis.

Querying from v$osstat ensures that an Oracle performance problem is not constrained by an external OS bottleneck. 

select * from v$osstat;
select * from dba_hist_osstat;
select * from dba_hist_system_event;

-- If you don't want to pay the fee to purchase AWR, use my vmstat table

select * from stats$vmstat

The v$osstat view has the following important run-time statistics:

  • idle_time:  The number (in hundredths of a second) that a processor has been idle, totaled over all processors

  • busy_time: The number(in hundredths of a second) that a processor has been busy executing user or kernel code, totaled over all processors

  • user_time: The number (in hundredths of a second) that a processor has been busy executing user code, totaled over all processors

  • sys_time: The number (in hundredths of a second) that a processor has been busy executing kernel code, totaled over all processors

  • iowait_time: The number (in hundredths of a second) that a processor has been waiting for I/O to complete, totaled over all processors

  • os_cpu_wait_time: The total number (in hundredths of a second) that processes have been in a ready state, waiting to be selected by the operating system scheduler to run

  • vm_page_in_bytes: Total number of bytes of data that have been paged in due to virtual memory paging

  • physical_memory_bytes: Total number of bytes of physical memory

  • load Current number of processes that are either running or in the ready state, waiting to be selected by the operating-system scheduler to run. On many platforms, this statistic reflects the average load over the past minute.

As we see, these are the same metrics that we can get from OS tools such as vmstat, top and glance, but they are ready to inspect within this Oracle view.

In addition to using v$osstat if you buy are extra cost AWR you can query the dba_hist_system_event table.

If you don't want to write your own OS monitoring scripts you can download a full set of Oracle OS monitoring scripts.

Advanced DBAs can use the techniques from my book Oracle Tuning: The Definitive Reference to enhance the v$osstat data with easy OS statistics collection.
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