Re: [POC] Faster processing at Gather node

On Fri, May 19, 2017 at 7:55 AM, Rafia Sabih
<rafia(dot)sabih(at)enterprisedb(dot)com> wrote:
> While analysing the performance of TPC-H queries for the newly developed
> parallel-operators, viz, parallel index, bitmap heap scan, etc. we noticed
> that the time taken by gather node is significant. On investigation, as per
> the current method it copies each tuple to the shared queue and notifies the
> receiver. Since, this copying is done in shared queue, a lot of locking and
> latching overhead is there.
>
> So, in this POC patch I tried to copy all the tuples in a local queue thus
> avoiding all the locks and latches. Once, the local queue is filled as per
> it's capacity, tuples are transferred to the shared queue. Once, all the
> tuples are transferred the receiver is sent the notification about the same.

What if, instead of doing this, we switched the shm_mq stuff to use atomics?

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