Global enqueue

[dba127]

Hi,

A data block's role is shifted from Local to Gloabl when it's transferred from one instance to another instance,but I didn't understand why an local enqueue become Global enqueue in RAC.Can anyone explain with an example,what role Global enqueue is playing in RAC & why it's termed as "Global"? I read Oracle documentation,but I couldn't understand?

Thanks..

[pando]

If you need to modify a row an TX enqueue is placed correct? And if you modify a row then it needs to be locked globally no? If one instance is locking the row then it must be done globally.

[dba127]

Hi Pando,

As per your saying "If one instance is locking the row then it must be done globally" which means TX enqueue information for that row will be updated globally in all RAC instances Library cache. Is my understanding right? Can you please explain this with a scenario?

Thanks a lot..

[pando]

If I run from instance 1

update x
set y = 1
where z = 1

Obviously when you run the same statement from instance 2 your session will be blocked.

So the enqueue is global no?