Comments on: Event snapshots

By: Slow Code « Oracle Scratchpad

Slow Code « Oracle Scratchpad — Wed, 30 Dec 2009 15:11:07 +0000

[...] (approximately) v$session_wait_history in older versions of Oracle. Rapid snapshots of the event histogram view. Comments [...]

By: Advanced Oracle Troubleshooting Guide, Part 7: Sampling latch holder statistics using LatchProf « Tanel Poder’s blog: Core IT for geeks and pros

Tue, 08 Jul 2008 11:56:25 +0000

[...] want to run this for too long at a time ( you could implement a short wait in there with a nice trick by Jonathan Lewis [...]

By: Jonathan Lewis

Jonathan Lewis — Tue, 17 Jun 2008 20:08:02 +0000

Jeroen,
Nice enhancement; it’s prompted me to write a version of the original code for 11g.

column event format a32 define m_event='db file%' define m_pause=20


with subq as (

        select

                event, wait_time_milli, sum(wait_count) wait_count

        from (

                select

                        event, wait_time_milli, -1 * wait_count  wait_count

                from    v$event_histogram

                where   event like '&m_event'

                union all

                select

                        null, jpl_numeric_wait( &m_pause ,-1), null

                from    dual

                union all

                select

                        event, wait_time_milli, wait_count

                from    v$event_histogram

                where   event like  '&m_event'

                )

        where

                wait_time_milli != -1

        group by

                event, wait_time_milli

        order by

                event, wait_time_milli

        )

select

        *

from

        subq

        pivot (

               max(wait_count)

               for wait_time_milli in (1,2,4,8,16,32)

        )

order by

        event

;
EVENT                        1      2      4      8     16     32

---------------------- ------- ------ ------ ------ ------ ------

db file parallel read        0      0      0      0      0      0

db file parallel write      18      0      0      0      0      0

db file scattered read       1      1      0      0      0      0

db file sequential read   1379      5      4     11     33     34

db file single write         0

I’ve just used the pivot() function here on my origrinal query, but changed the equality to a like. This has lined up a few similar events in a nice tabular form.

If you want to get clever, you could even change the like to some variant of a regexp() function and pick out (say) all file reads and writes.

Update: Note that the pivot() clause is limited to keep the output readable on WordPress.

By: Jeroen

Jeroen — Mon, 16 Jun 2008 10:56:09 +0000

I tried this out on 11g and used the new pivot clause to produce a cross-tab from multiple collection samples.

create table evh ( snap_time date, event varchar2(30), wait_time_milli number, wait_time_count number );


insert into evh

select sysdate snap_time, iv.event event, iv.wait_time_milli, iv.wait_time_count

  from (

select

     event, wait_time_milli, sum(wait_count) wait_time_count

  from (

     select

             event, wait_time_milli, -1 * wait_count  wait_count

     from    v$event_histogram

     where   event = '&m_event'

     union all

     select

             null, jpl_numeric_wait( &m_pause ,-1), null

     from    dual

     union all

     select

             event, wait_time_milli, wait_count

     from    v$event_histogram

     where   event = '&m_event'

     )

  where

     wait_time_milli != -1

  group by

     event, wait_time_milli

  order by

    event, wait_time_milli

) iv;

with data as ( select to_char(snap_time,'dd-mon-yy hh24:mi:ss'), event, wait_time_milli, wait_time_count from evh ) select * from data pivot ( max(wait_time_count) for wait_time_milli in (1,2,4,8,16,32,64,128,256,512,1024,2048 ) ) order by 2,1

By: Event Histograms - 2 « Oracle Scratchpad

Event Histograms - 2 « Oracle Scratchpad — Mon, 16 Jun 2008 09:11:22 +0000

[...] Event Histograms - 2 Filed under: Statspack, Troubleshooting — Jonathan Lewis @ 8:38 pm UTC Jan 31,2007 [Forward to part 3] [...]

By: lascoltodelvenerdi

lascoltodelvenerdi — Mon, 16 Jun 2008 08:43:04 +0000

Nice one.

Times ago, I was thinking about redefining some Oracle V$iews, or introduce some new ones, so I can have history in them.

They would be great for historic-events-analysis.