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Tanel Poder

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Updated: 13 hours 25 min ago

Advanced Oracle Troubleshooting Guide – Part 12: control file reads causing enq: SQ – contention waits?

Fri, 2015-04-24 17:23

Vishal Desai systematically troubleshooted an interesting case where the initial symptoms of the problem showed a spike of enq: SQ – contention waits, but he dug deeper – and found the root cause to be quite different. He followed the blockers of waiting sessions manually to reach the root cause – and also used my @ash/ash_wait_chains.sql and @ash/event_hist.sql scripts to extract the same information more conveniently (note that he had modified the scripts to take AWR snap_ids as time range parameters instead of the usual date/timestamp):

Definitely worth a read if you’re into troubleshooting non-trivial performance problems :)

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Sqlplus is my second home, part 8: Embedding multiple sqlplus arguments into one variable

Sun, 2015-03-29 15:23

I’ve updated some of my ASH scripts to use these 4 arguments in a standard way:

  1. What ASH columns to display (and aggregate by)
  2. Which ASH rows to use for the report (filter)
  3. Time range start
  4. Time range end

So this means whenever I run ashtop (or dashtop) for example, I need to type in all 4 parameters. The example below would show top SQL_IDs only for user SOE sessions from last hour of ASH samples:

SQL> @ashtop sql_id username='SOE' sysdate-1/24 sysdate

    Total
  Seconds     AAS %This   SQL_ID        FIRST_SEEN          LAST_SEEN           DIST_SQLEXEC_SEEN
--------- ------- ------- ------------- ------------------- ------------------- -----------------
     2271      .6   21% | 56pwkjspvmg3h 2015-03-29 13:13:16 2015-03-29 13:43:34               145
     2045      .6   19% | gkxxkghxubh1a 2015-03-29 13:13:16 2015-03-29 13:43:14               149
     1224      .3   11% | 29qp10usqkqh0 2015-03-29 13:13:25 2015-03-29 13:43:32               132
      959      .3    9% | c13sma6rkr27c 2015-03-29 13:13:19 2015-03-29 13:43:34               958
      758      .2    7% |               2015-03-29 13:13:16 2015-03-29 13:43:31                 1

When I want more control and specify a fixed time range, I can just use the ANSI TIMESTAMP (or TO_DATE) syntax:

SQL> @ashtop sql_id username='SOE' "TIMESTAMP'2015-03-29 13:00:00'" "TIMESTAMP'2015-03-29 13:15:00'"

    Total
  Seconds     AAS %This   SQL_ID        FIRST_SEEN          LAST_SEEN           DIST_SQLEXEC_SEEN
--------- ------- ------- ------------- ------------------- ------------------- -----------------
      153      .2   22% | 56pwkjspvmg3h 2015-03-29 13:13:29 2015-03-29 13:14:59                 9
      132      .1   19% | gkxxkghxubh1a 2015-03-29 13:13:29 2015-03-29 13:14:59                 8
       95      .1   14% | 29qp10usqkqh0 2015-03-29 13:13:29 2015-03-29 13:14:52                 7
       69      .1   10% | c13sma6rkr27c 2015-03-29 13:13:31 2015-03-29 13:14:58                69
       41      .0    6% |               2015-03-29 13:13:34 2015-03-29 13:14:59                 1

Note that the arguments 3 & 4 above are in double quotes as there’s a space within the timestamp value. Without the double-quotes, sqlplus would think the script has total 6 arguments due to the spaces.

I don’t like to type too much though (every character counts!) so I was happy to see that the following sqlplus hack works. I just defined pairs of arguments as sqlplus DEFINE variables as seen below (also in init.sql now):

  -- geeky shorcuts for producing date ranges for various ASH scripts
  define     min="sysdate-1/24/60 sysdate"
  define  minute="sysdate-1/24/60 sysdate"
  define    5min="sysdate-1/24/12 sysdate"
  define    hour="sysdate-1/24 sysdate"
  define   2hours="sysdate-1/12 sysdate"
  define  24hours="sysdate-1 sysdate"
  define      day="sysdate-1 sysdate"
  define    today="TRUNC(sysdate) sysdate"

And now I can type just 3 arguments instead of 4 when I run some of my scripts and want some predefined behavior like seeing last 5 minutes’ activity:

SQL> @ashtop sql_id username='SOE' &5min

    Total
  Seconds     AAS %This   SQL_ID        FIRST_SEEN          LAST_SEEN           DIST_SQLEXEC_SEEN
--------- ------- ------- ------------- ------------------- ------------------- -----------------
      368     1.2   23% | gkxxkghxubh1a 2015-03-29 13:39:34 2015-03-29 13:44:33                37
      241      .8   15% | 56pwkjspvmg3h 2015-03-29 13:40:05 2015-03-29 13:44:33                25
      185      .6   12% | 29qp10usqkqh0 2015-03-29 13:39:40 2015-03-29 13:44:33                24
      129      .4    8% | c13sma6rkr27c 2015-03-29 13:39:35 2015-03-29 13:44:32               129
      107      .4    7% |               2015-03-29 13:39:34 2015-03-29 13:44:33                 1

That’s it, I hope this hack helps :-)

By the way – if you’re a command line & sqlplus fan, check out the SQLCL command line “new sqlplus” tool from the SQL Developer team! (you can download it from the SQL Dev early adopter page for now).

 

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Oracle Exadata Performance: Latest Improvements and Less Known Features

Tue, 2015-03-24 08:57

Here are the slides of a presentation I did at the IOUG Virtual Exadata conference in February. I’m explaining the basics of some new Oracle 12c things related to Exadata, plus current latest cellsrv improvements like Columnar Flash Cache and IO skipping for Min/Max retrieval using Storage Indexes:

Note that Christian Antognini and Roger MacNicol have written separate articles about some new features:

Enjoy!

 

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Public Appearances 2015

Tue, 2015-02-10 16:14

Here’s where I’ll hang out in the following months:

11-12 Feb 2015: IOUG Exadata SIG Virtual Conference (free online event)

  • Presentation: Exadata Performance: Latest Improvements and Less Known Features
  • It’s a free online event, so sign up here

18-19 Feb 2015: RMOUG Training Days (in Denver)

  • I won’t speak there this year, but plan to hang out on Wednesday evening and drink beer
  • More info here

1-5 March 2015: Hotsos Symposium 2015

31 May – 2 June 2015: Enkitec E4

  • Even more awesome Exadata (and now also Hadoop) content there!
  • I plan to speak there again, about Exadata performance and/or integrating Oracle databases with Hadoop
  • More info here

Advanced Oracle Troubleshooting v3.0 training

  • One of the reasons why I’ve been so quiet in recent months is that I’ve been rebuilding my entire Advanced Oracle Troubleshooting training material from ground up.
  • This new seminar focuses on systematic Oracle troubleshooting and internals of database versions all the way to Oracle 12c.
  • I will launch the AOT seminar v3.0 in early March – you can already register your interest here!

 

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