On 17 November 2015 at 11:48, Amit Kapila <amit.kapil...@gmail.com> wrote:
> On Tue, Nov 17, 2015 at 5:04 PM, Simon Riggs <si...@2ndquadrant.com> > wrote: > >> On 17 November 2015 at 11:27, Amit Kapila <amit.kapil...@gmail.com> >> wrote: >> >> We are trying to speed up real cases, not just benchmarks. >>>> >>>> So +1 for the concept, patch is going in right direction though lets do >>>> the full press-up. >>>> >>>> >>> I have mentioned above the reason for not doing it for sub transactions, >>> if >>> you think it is viable to reserve space in shared memory for this >>> purpose, then >>> I can include the optimization for subtransactions as well. >>> >> >> The number of subxids is unbounded, so as you say, reserving shmem isn't >> viable. >> >> I'm interested in real world cases, so allocating 65 xids per process >> isn't needed, but we can say is that the optimization shouldn't break down >> abruptly in the presence of a small/reasonable number of subtransactions. >> >> > I think in that case what we can do is if the total number of > sub transactions is lesser than equal to 64 (we can find that by > overflowed flag in PGXact) , then apply this optimisation, else use > the existing flow to update the transaction status. I think for that we > don't even need to reserve any additional memory. Does that sound > sensible to you? > I understand you to mean that the leader should look backwards through the queue collecting xids while !(PGXACT->overflowed) No additional shmem is required -- Simon Riggs http://www.2ndQuadrant.com/ <http://www.2ndquadrant.com/> PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
