Re: Scaling XLog insertion (was Re: Moving more work outside WALInsertLock)

On 06.03.2012 17:12, Tom Lane wrote:
> Heikki Linnakangas<heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
>> On 06.03.2012 14:52, Fujii Masao wrote:
>>> This also strikes me that the usage of the spinlock insertpos_lck might
>>> not be OK in ReserveXLogInsertLocation() because a few dozen instructions
>>> can be performed while holding the spinlock....
>
>> I admit that block is longer than any of our existing spinlock blocks.
>> However, it's important for performance. I tried using a lwlock earlier,
>> and that negated the gains. So if that's a serious objection, then let's
>> resolve that now before I spend any more time on other aspects of the
>> patch. Any ideas how to make that block shorter?
>
> How long is the current locked code exactly --- does it contain a loop?

Perhaps best if you take a look for yourself, the function is called
ReserveXLogInsertLocation() in patch. It calls a helper function called
AdvanceXLogRecPtrToNextPage(ptr), which is small and could be inlined.
It does contain one loop, which iterates once for every WAL page the
record crosses.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com