Re: Resource Owner reassign Locks

On Mon, Jun 11, 2012 at 9:30 PM, Amit Kapila <amit.kapila@huawei.com> wrote:
>> Yes, that means the list has over-flowed.  Once it is over-flowed, it
>> is now invalid for the reminder of the life of the resource owner.

> Don't we need any logic to clear the reference of locallock in owner->locks
> array.

I don't think so.  C doesn't ref count its pointers.

> MAX_RESOWNER_LOCKS - How did you arrive at number 10 for it. Is there any
> specific reason for 10.

I instrumented the code to record the maximum number of locks held by
a resource owner, and report the max when it was destroyed.  (That
code is not in this patch).  During a large pg_dump, the vast majority
of the resource  owners had maximum locks of 2, with some more at 4
and 6.    Then there was one resource owner, for the top-level
transaction, at tens or hundreds of thousands (basically one for every
lockable object).  There was little between 6 and this top-level
number, so I thought 10 was a good compromise, safely above 6 but not
so large that searching through the list itself was likely to bog
down.

Also, Tom independently suggested the same number.


>> Should it emit a FATAL rather than an ERROR?  I thought ERROR was
>> sufficient to make the backend quit, as it is not clear how it could
>> meaningfully recover.
>
> I am not able to visualize any valid scenario in which it can happen unless
> some corruption happens.
> If this happens, user can close all statements and abort its transactions.
> According to me ERROR is okay. However in the message "Can't find lock to
> remove",  it could be better,
> if there is information about resource owner and lock.

I think we might end up changing that entirely once someone more
familiar with the error handling mechanisms takes a look at it.  I
don't think that lock tags have good human readable formats, and just
a pointer dump probably wouldn't be much use when something that can
never happen has happened.  But I'll at least add a reference to the
resource owner if this stays in.

Thanks,

Jeff