Re: Speed up Clog Access by increasing CLOG buffers

On Thu, Nov 26, 2015 at 11:32 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> On Tue, Nov 17, 2015 at 6:30 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>>
>> On 17 November 2015 at 11:48, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>>>
>>>
>>> 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
>>
>
> Okay, as discussed I have handled the case of sub-transactions without
> additional shmem in the attached patch. Apart from that, I have tried
> to apply this optimization for Prepared transactions as well, but as
> the dummy proc used for such transactions doesn't have semaphore like
> backend proc's, so it is not possible to use such a proc in group status
> updation as each group member needs to wait on semaphore. It is not tad
> difficult to add the support for that case if we are okay with creating
> additional
> semaphore for each such dummy proc which I was not sure, so I have left
> it for now.

Is this proposal instead of, or in addition to, the original thread
topic of increasing clog buffers to 64?

Thanks,

Jeff