Comments on: Oracle RAC, v$, and gv$

By: Jag

Jag — Sat, 02 Aug 2008 00:30:51 +0000

I too would like to know that query, if it is ok for you to send me on my email id.

Thanks in advace.

By: The_cat

The_cat — Fri, 16 May 2008 17:18:16 +0000

Hi dash.
I’m having lots of problems with locks en a rac enviroment.
You mencioned your internal script and i agree with you about posting it.
But can you please send it to me directly?

[Email address removed. -Ed.]
Thanks in advance.

By: dash

dash — Tue, 06 May 2008 16:02:54 +0000

Thanks for the feedback Patrick - you are correct with your suggestions. I was going with simplicity as much as possible to illustrate the difference between the types of views - I should have remembered that my target audience are sticklers for details (keeps me on my toes!). I’m very glad you made the comments to clarify.

I would have posted our internal script for reference as it is a fantastic one, but I didn’t write it and felt uncomfortable posting someone else’s intellectual property. The great thing about the gv$ views is that they can be your best friend and your worst enemy.

Glad that this has helped - that makes my day!

By: Patrick

Patrick — Tue, 06 May 2008 15:13:30 +0000

Hi David

Thanks for posting this, which I have already found useful. I did notice some issues with it and have posted a revised version below.

Firstly your SQL only joined the instance ids between the gv$lock and gv$session views for the blocking session (l1.inst_id = s1.inst_id). This is also needed for the blocked session (l2.inst_id = s2.inst_id), otherwise it may show too many sessions as blocked.

l2.id2 = l2.id2, will always evaluate to true and should be l1.id2 = l2.id2.

On my RAC database I found that the “block” column held a 2 for the blocking session, not a 0 or 1 as stated in the documentation. I therefore needed to replace l1.BLOCK1=1 with l1.BLOCK1 > 0.

select distinct s1.username || ‘@’ || s1.machine
|| ‘ ( INST=’ || s1.inst_id || ‘ SID=’ || s1.sid || ‘ ) is blocking ‘
|| s2.username || ‘@’ || s2.machine || ‘ ( INST=’ || s1.inst_id || ‘ SID=’ || s2.sid || ‘ ) ‘
AS blocking_status
from gv$lock l1, gv$session s1, gv$lock l2, gv$session s2
where s1.sid=l1.sid and s2.sid=l2.sid
and s1.inst_id=l1.inst_id and s2.inst_id=l2.inst_id
and l1.block > 0 and l2.request > 0
and l1.id1 = l2.id1 and l1.id2 = l2.id2;