Re: Reducing ClogControlLock contention

On Tue, Aug 11, 2015 at 7:27 PM, Simon Riggs <simon@2ndquadrant.com> wrote:
>
> On 11 August 2015 at 14:53, Amit Kapila <amit.kapila16@gmail.com> wrote:
>  
>>
>> One more point here why do we need CommitLock before calling
>> SimpleLruReadPage_ReadOnly() in the patch and if it is not required,
>> then can we use LWLockAcquire(shared->buffer_locks[slotno], LW_EXCLUSIVE);
>> instead of CommitLock?
>
>
> That prevents read only access, not just commits, so that isn't a better suggestion.

read only access of what (clog page?)?

Here we are mainly doing three operations read clog page, write transaction status

on clog page and update shared control state.  So basically two resources are

involved clog page and shared control state, so which one of those you are talking?

Apart from above, in below code, it is assumed that we have exclusive lock on

clog page which we don't in the proposed patch as some one can read the

same page while we are modifying it. In current code, this assumption is valid

because during Write we take CLogControlLock in Exclusive mode and while

Reading we take the same in Shared mode.