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Oracle Table I/O and buffer efficiency monitoring

Oracle Database Tips by Donald Burleson

In  Oracle 10g we have the dba_hist_seg_stat table with a wealth of information about all active segments within the database.  It also contains details about the logical I/O (buffer gets) and physical reads (disk reads) for all of your important tables and indexes.

The dba_hist_seg_stat table has information of table usage, especially the buffer gets (logical reads), disk reads (physical reads) and the number of full-scans experienced by any database segment:

 LOGICAL_READS_TOTAL                                   
 LOGICAL_READS_DELTA                                   
 BUFFER_BUSY_WAITS_TOTAL                         
 BUFFER_BUSY_WAITS_DELTA                         
 DB_BLOCK_CHANGES_TOTAL                          
 DB_BLOCK_CHANGES_DELTA                          
 PHYSICAL_READS_TOTAL                                 
 PHYSICAL_READS_DELTA                                 
 PHYSICAL_WRITES_TOTAL                               
 PHYSICAL_WRITES_DELTA                               
 PHYSICAL_READS_DIRECT_TOTAL                 
 PHYSICAL_READS_DIRECT_DELTA                 
 PHYSICAL_WRITES_DIRECT_TOTAL               
 PHYSICAL_WRITES_DIRECT_DELTA               

 TABLE_SCANS_TOTAL                                        

 TABLE_SCANS_DELTA

As I note in my book Oracle Tuning: The Definitive Reference, we can quickly plot this information for trending and predictions:

select
   to_char(begin_interval_time,'yy/mm/dd/hh24') c1,
   logical_reads_total c2,
   physical_reads_total c3
from
   dba_hist_seg_stat     s,
   dba_hist_seg_stat_obj o,
   dba_hist_snapshot     sn
where
   o.owner = 'SCHEMA_07'
and
   s.obj# = o.obj#
and
   sn.snap_id = s.snap_id
and
   object_name = 'GEN_PERSON'
order by
   begin_interval_time;

Now, a quick paste into the MS Excel spreadsheet and the chart wizard gives us a great trend line for physical reads versus buffer gets for the specific Oracle table:

As we can see, the dba_hist_seg_stat view is a wonderful way to capture object-level space and usage information for predictive modeling purposes.

This is part of my latest book "Oracle Tuning: The Definitive Reference". 

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts:


 

 

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Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

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