> On 2 Jan 2024, at 19:23, Robert Haas <robertmh...@gmail.com> wrote:
>
>>
>> And it would be even better if page for transaction statuses would be
>> determined by backend id somehow. Or at least cache line. Can we allocate a
>> range (sizeof(cacheline)) of xids\subxids\multixacts\whatever for each
>> backend?
>
> I don't understand how this could work. We need to be able to look up
> transaction status by XID, not backend ID.
When GetNewTransactionId() is called we can reserve 256 xids in backend local
memory. This values will be reused by transactions or subtransactions of this
backend. Here 256 == sizeof(CacheLine).
This would ensure that different backends touch different cache lines.
But this approach would dramatically increase xid consumption speed on patterns
where client reconnects after several transactions. So we can keep unused xids
in procarray for future reuse.
I doubt we can find significant performance improvement here, because false
cache line sharing cannot be _that_ bad.
Best regards, Andrey Borodin.
