Thursday, 20 October 2016

AWR Summary Data Extracts

A long time ago (in a galaxy far away) I wrote a series of blog posts about directly extracting useful sets of data from the AWR snapshots in the DBA_HIST tables for subsequent analysis and graphing using things like Excel. This post is to summarise where I got to on this, and provide links back to the main posts for future reference.

A guiding principle of my approach was that I wanted to avoid the "mother of all AWR queries" that would extract every possible data value from all DBA_HIST tables for all snapshots, as it would be a really big and complex query (meaning difficult to debug if a mistake was introduced anywhere) and it could use up a lot of system resources and take some time to finish each time it was executed. Instead I prefer the smaller, targeted type of query that extracts just what you need from the minimum number of AWR tables, because it is simpler to understand and will be quicker to execute. That said, you could extend my approach of one sub-query per DBA_HIST table and include all of the main AWR snapshot tables into one single query, and then create a view using it. This would allow you to write simpler analysis queries later on against the view, without needing to need to know the details of all the various sub-queries and DBA_HIST tables.

Along the way I covered the following main topics in the blog posts:-
Although I did not post a query that merged all the different component sub-queries together, I did post a minimal Summary AWR Query at the end to show how you could use the basic AWR data in practise to look at the overall performance and behaviour of a system. By extending the main SELECT of the final query itself, you can add extra columns of data you want into the output, without any changes to the various component sub-queries (the "with" or Common Table Expressions). To put it another way, if there is some extra AWR data you want extracted then you need to work out which of the main data sets it falls under, and then which columns or rows in that AWR data set the data you want is stored in.

For instance here is another variation of the AWR Summary Query that also extracts the number of SQL statements executed, the separate wait times for User I/O and Cluster waits (normalised to a percentage of the total wait time in the snapshot), physical reads (normalised to a per second value), average disk read and redo write times.
 * Name      : awr_sum_lite
 * Purpose   : Minimal one line summary of each AWR snapshot from a day
 * Descrip'n : Based on awr_sum_range with unneeded stuff deleted
 *             Only key essential stuff is output:
 *                 SQL executions / sec, #User calls / sec
 *                 Average Active Sessions, Wait % of Busy time
 *                 Cluster Wait % of wait time, User I/O % of wait time
 *                 Avg disk read time, Avg redo write time, #Disk reads / sec
 *             Values directly calculated, rather than raw underlying values
 * Usage     : @awr_sum_lite
 * Assumption: Want the last 4 whole days
 *               Which is from midnight 4 days ago to last midnight
 * To Do     : 
set feedback off
set heading off
set newpage none
set verify off
set linesize 1000
set pages 28
set trimout on
set trimspool on
select ' ' from dual ;
select '                 AWR Lite Summary Report' from dual ;
select '                 =======================' from dual ;
-- select ' ' from dual ;
-- select ''
--    || '<= Database Time =>'
--    || '<= System Statistics ==>'
--    || '<== Waits ================>'
--  from dual ;
set newpage 1
set heading on
col snap_time           format a15      heading 'SNAP TIME'
col aas                 format 90.0     heading 'AAS'
col wait_pct            format 990.0    heading 'WAIT%'
col cluster_pct         format 90.0     heading 'CLUS%'
col user_io_pct         format 90.0     heading 'UIO%'
col executions_sec      format 9,990    heading 'EXEC/S'
col user_calls_sec      format 9,990    heading 'UCALL/S'
col physical_reads_sec  format 9,990    heading 'READS/S'
col avg_disk_read       format 990.0    heading '(MS)|AV RD'
col avg_redo_write      format 990.0    heading '(MS)|REDO W'
snaps as 
(select snap_id
      , dbid
      , end_snap_time
      , snap_interval
      , extract (second from snap_interval) 
       + (extract (minute from snap_interval) 
          + (extract (hour from snap_interval)
             + (extract (day from snap_interval) * 24)
             ) * 60
          ) * 60 snap_duration
  from (select csnaps.snap_id
             , csnaps.dbid
             , min (csnaps.end_interval_time) end_snap_time
             , min (csnaps.end_interval_time) - min (csnaps.begin_interval_time) snap_interval
          from dba_hist_snapshot csnaps
         group by csnaps.snap_id, csnaps.dbid
) -- snaps
, systimes as 
-- One row per Database Time Model with change in value between snapshots
(select systime.snap_id
      , systime.dbid
      , systime.stat_name
      , sum (systime.value - psystime.value) value
         from dba_hist_sys_time_model systime, dba_hist_sys_time_model psystime
        where systime.snap_id = psystime.snap_id + 1
          and systime.dbid = psystime.dbid
          and systime.instance_number = psystime.instance_number
          and systime.stat_id = psystime.stat_id
-- Assume if stat_id the same so is the stat_name
        group by systime.snap_id, systime.dbid, systime.stat_name
) -- systimes
, sysstats as 
-- One row per System Statistic with change in value between snapshots
(select sysstat.snap_id
      , sysstat.dbid
      , sysstat.stat_name
      , sum (sysstat.value - psysstat.value) value
         from dba_hist_sysstat sysstat, dba_hist_sysstat psysstat
        where sysstat.snap_id = psysstat.snap_id + 1
          and sysstat.dbid = psysstat.dbid
          and sysstat.instance_number = psysstat.instance_number
          and sysstat.stat_id = psysstat.stat_id
-- Assume if stat_id the same so is the stat_name
        group by sysstat.snap_id, sysstat.dbid, sysstat.stat_name
) -- sysstats
, syswaits as 
-- One row for total wait time, plus break down into major wait classes, and events
(select syswaitevents.snap_id
      , syswaitevents.dbid
      , sum (syswaitevents.time_waited_micro) all_wait_time
      , sum (decode (syswaitevents.wait_class, 'Commit',      syswaitevents.time_waited_micro, 0)) commit_time
      , sum (decode (syswaitevents.wait_class, 'Cluster',     syswaitevents.time_waited_micro, 0)) cluster_time
      , sum (decode (syswaitevents.wait_class, 'Concurrency', syswaitevents.time_waited_micro, 0)) concurrency_time
      , sum (decode (syswaitevents.wait_class, 'Network',     syswaitevents.time_waited_micro, 0)) network_time
      , sum (decode (syswaitevents.wait_class, 'System I/O',  syswaitevents.time_waited_micro, 0)) system_io_time
      , sum (decode (syswaitevents.wait_class, 'User I/O',    syswaitevents.time_waited_micro, 0)) user_io_time
        (select sysevent.snap_id
              , sysevent.dbid
              , sysevent.wait_class
              , sysevent.event_name
              , sum (sysevent.time_waited_micro - psysevent.time_waited_micro) time_waited_micro
              , sum (sysevent.total_waits - psysevent.total_waits) wait_count
           from dba_hist_system_event sysevent, dba_hist_system_event psysevent
          where sysevent.snap_id = psysevent.snap_id + 1
            and sysevent.dbid = psysevent.dbid
            and sysevent.instance_number = psysevent.instance_number
            and sysevent.event_id = psysevent.event_id
            and sysevent.wait_class != 'Idle'  -- Ignore Idle wait events
          group by sysevent.snap_id
                 , sysevent.dbid
                 , sysevent.wait_class
                 , sysevent.event_name
        ) syswaitevents
  group by syswaitevents.snap_id
         , syswaitevents.dbid
) -- syswaits
-- Average Active Sessions, Wait % of Busy time
-- Cluster Wait % of wait time, User I/O % of wait time
-- SQL executions / sec, #User calls / sec
-- Avg disk read time, Avg redo write time, #Disk reads / sec
select to_char (snaps.end_snap_time, 'DD/MM/YY HH24:MI') snap_time
     , (user_calls_st.value / snaps.snap_duration)              user_calls_sec
     , (execs.value / snaps.snap_duration)                      executions_sec
     , (dbtime.value / 1000000)       / snaps.snap_duration     aas
-- If database active time is 1% of duration time or less ignore wait (0)
     , case when (dbtime.value / (1000 * snaps.snap_duration) ) > 1
            then (100 * syswaits.all_wait_time  / dbtime.value)
            else 0.0
       end wait_pct
     , (100 * syswaits.cluster_time   / syswaits.all_wait_time) cluster_pct
     , (100 * syswaits.user_io_time   / syswaits.all_wait_time) user_io_pct
     , (phys_reads.value / snaps.snap_duration)                 physical_reads_sec
     , (syswaits.user_io_time / phys_reads.value) / 1000        avg_disk_read
     , (redo_time_st.value * 10 / redo_write_st.value)          avg_redo_write
  from snaps
     join (select * from systimes where stat_name = 'DB time') dbtime
       on snaps.snap_id = dbtime.snap_id and snaps.dbid = dbtime.dbid
     join syswaits
       on snaps.snap_id = syswaits.snap_id and snaps.dbid = syswaits.dbid
     join (select * from sysstats where stat_name = 'execute count') execs
       on snaps.snap_id = execs.snap_id and snaps.dbid    = execs.dbid
     join (select * from sysstats where stat_name = 'user calls') user_calls_st
       on snaps.snap_id = user_calls_st.snap_id and snaps.dbid = user_calls_st.dbid
     join (select * from sysstats where stat_name = 'redo writes') redo_write_st
       on snaps.snap_id = redo_write_st.snap_id and snaps.dbid  = redo_write_st.dbid
     join (select * from sysstats where stat_name = 'redo write time') redo_time_st
       on snaps.snap_id = redo_time_st.snap_id and snaps.dbid  = redo_time_st.dbid
     join (select * from sysstats where stat_name = 'physical reads') phys_reads
       on snaps.snap_id = phys_reads.snap_id and snaps.dbid    = phys_reads.dbid
 where snaps.end_snap_time between 
       (trunc (sysdate) - 4) and (trunc (sysdate))
 order by snaps.end_snap_time
set feedback on
set lines 80
This query provides what I believe are a good, minimal set of useful measurements of activity and relative performance of an Oracle database. It allows easy viewing of relative activity (Average Active Sessions, User Calls / sec), waiting time as a percentage of database time, the main types of wait occurring (User I/O and Cluster), and some key disk I/O measurements (physical reads / sec, average disk read time, average redo write time). From these you can see how active the system is, whether any significant waits are occurring, and if they are I/O related, and see how these change over time between AWR snapshots.

Of course everyone has a different opinion of what the most important measurements are on an Oracle database. My key message here is that the approach I have followed lets you customise these queries to report out the performance and activity measurements you want from the data captured in the AWR snapshots. So if you want a different set of data values reported out, then it should be relatively easy to modify these queries to get what you want.

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