Oracle Session Snapper v3.10

Tanel Poder


Hi all, long time no see!  =8-)

Now as I’m done with the awesome Hotsos Symposium (and the training day which I delivered) and have got some rest, I’ll start publishing some of the cool things I’ve been working on over the past half a year or so.

The first is Oracle Session Snapper version 3!

There are some major improvements in Snapper 3, like ASH style session activity sampling!

When you troubleshoot a session’s performance (or instance performance) then the main things you want to know first are very very simple:

  1. Which SQL statements are being executed
  2. What are they doing, are they working on CPU or waiting.
  3. If waiting, then for what

Often this is enough for troubleshooting what’s wrong. For example, if a session is waiting for a lock, then wait interface will show you that. If a single SQL statement is taking 99% of total response time, the V$SESSION (ASH style) samples will point out the problem SQL and so on. Simple stuff.

However there are cases where you need to go beyond wait interface and use V$SESSTAT (and other) counters and even take a “screwdriver” and open Oracle up from outside by stack tracing :-)

When I wrote the first version of Snapper for my own use some 4-5 years ago I wrote it mainly having the “beyond wait interface” part in mind. So I focused on V$SESSTAT and various other counters and left the basic troubleshooting to other tools. I used to manually sample V$SESSION/V$SESSION_WAIT a few times in a row to get a rough overview of what a session was doing or some other special-purpose scripts.

However after Snapper got more popular and I started getting some feedback about it I saw the need for covering more with Snapper, not just the “beyond wait interface” part, but also the “wait interface” and “which SQL” part too.

So, now I’m presenting Snapper v3 which does all the 3 points above using ASH style V$SESSION sampling and it still has the first step to “beyond wait interface” part in it, which is very useful for advanced performance troubleshooting and diagnosis – I’m talking about the V$SESSTAT counters above.

I’ve made some syntax changes in Snapper too and right now the v3 doesn’t work on Oracle 9.2 (it will work some day :)

To give you an idea of the new ASH style sampling capabilities, heres some example output:

SQL> @snapper ash=sid+event+wait_class,ash1=plsql_object_id+plsql_subprogram_id+sql_id,ash2=program+module+action 5 1 all

-- Session Snapper v3.10 by Tanel Poder @ E2SN ( ) --------------------------------------------------------------
Active% |    SID | EVENT                     | WAIT_CLASS
-------------------------------------------------------------- 100% |    133 | db file scattered read    | User I/O 5% |    165 | control file parallel wri | System I/O 2% |    162 | ON CPU                    | ON CPU 2% |    167 | db file parallel write    | System I/O 2% |    166 | log file parallel write   | System I/O
--------------------------------------------------- Active% | PLSQL_OBJE | PLSQL_SUBP | SQL_ID --------------------------------------------------- 77% |            |            | a5xyjp9gt796s 23% |            |            | 4g4u44bk830ms 12% |            |            |
------------------------------------------------------------------------------------------- Active% | PROGRAM                   | MODULE                    | ACTION ------------------------------------------------------------------------------------------- 100% | sqlplus@mac01 (TNS V1-V3) | sqlplus@mac01 (TNS V1-V3) | 5% | oracle@solaris02 (CKPT)   |                           | 2% | oracle@solaris02 (DBW0)   |                           | 2% | oracle@solaris02 (CJQ0)   |                           | 2% | oracle@solaris02 (LGWR)   |                           | --  End of ASH snap 1, end=2010-03-22 17:35:06, seconds=5, samples_taken=43

You can read some usage examples and download it here:

P.S. People who attended Hotsos Symposium Training Day where I demoed the initial version of Snapper v3 – download the new version from above link (v3.10), it’s much more flexible than the one I demoed couple of weeks ago!

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