Comments on: Diagnostics For Database Hang

By: Amit

Amit — Thu, 07 Aug 2008 03:53:25 +0000

You need to first check database alert log for any errors/issues. Sometimes errors like ORA-600 and ORA-7445 are reported which could be causing the hang. Also when hangs are caused by latching or enqueue issues such as “PMON failed to acquire latch”, then you will see that systemstate will be dumped automatically. This can be uploaded to metalink.

Also use OS utilities like top,vmstat if there is CPU contention and OS logs (/var/log/messages on linux).
In case your Database is hung in such a way that you cannot run queries, then you need to take Systemstate dump. You can use below note for same in 8i/9i

Note 121779.1-Taking a SYSTEMSTATE dump when you cannot CONNECT to Oracle.

In case of 10g, you can use prelim to connect to database.
e.g
sqlplus -prelim “/ as sysdba” and then take systemstate and hanganalyze

-Amit

By: siva

siva — Thu, 07 Aug 2008 03:07:17 +0000

Very good information on database hang.
But i have few questions on this:

If database hung,we will not generate any reports,not running queries also.In this situation,what is the first step we ill take?

By: Amit

Amit — Sat, 05 Apr 2008 01:28:00 +0000

Aarya,You can use P1,P2,P3 values to diagnose the parameters for wait event. e.g You see event ‘latch free’ as considerable wait event, then
P1 = Latch address
P2 = Latch number

Now you can identify the latch name from V$LATCHNAME
SELECT * FROM v$latchname WHERE latch# =P2;
Moreover there can be situation where many sessions are waiting on same latch anf their P1 and P2 values are same say it points to Shared Pool Latch. From this we can be sure that some latching issue is causing the Database Hang.I will try to take up a case study sometime so that it can be more clear.And for your second question, you can refer to
Note 121779.1-Taking a SYSTEMSTATE dump when you cannot CONNECT to Oracle.

It is already mentioned in the post.In case of 10g, you can use prelim to connect to database.
e.g
sqlplus -prelim “/ as sysdba”

Cheers
Amit

By: Aaryadba

Aaryadba — Fri, 21 Mar 2008 14:36:00 +0000

Hi Piyush,

Very good information on database hang.
But i have few questions on this:

-What does p1,p2,p3 represents in v$session_wait and what are their significanse here.
- I have faced this situation many a times but i was not able to login to database when the hang occured, so what to do in that case, i.e how to generate dumps.