Re: Reduce ProcArrayLock contention

On Wed, Aug 5, 2015 at 8:30 AM, Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com> wrote:
> I actually even thought if we can define some macros or functions to work on
> atomic list of PGPROCs. What we need is:
>
> - Atomic operation to add a PGPROC to list list and return the head of the
> list at the time of addition
> - Atomic operation to delink a list from the head and return the head of the
> list at that time
> - Atomic operation to remove a PGPROC from the list and return next element
> in the list
> - An iterator to work on the list.

The third operation is unsafe because of the A-B-A problem. That's
why the patch clears the whole list instead of popping an individual
entry.

> This will avoid code duplication when this infrastructure is used at other
> places. Any mistake in the sequence of read/write/cas can lead to a hard to
> find bug.
>
> Having said that, it might be ok if we go with the current approach and then
> revisit this if and when other parts require similar logic.

Yeah, I don't think we should assume this will be a generic facility.
We can make it one later if needed.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company