Re: Reducing walreceiver latency with a latch

On 13/09/10 14:47, Thom Brown wrote:
> On 13 September 2010 12:40, Heikki Linnakangas
> <heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
>> Now that we have the wonderful latch facility, let's use it to reduce the
>> delay between receiving a piece of WAL and applying in the standby.
>> Currently, the startup process polls every 100ms to see if new WAL has
>> arrived, which adds an average a 50 ms delay between a transaction commit in
>> the master and it appearing as committed in a hot standby server. The latch
>> patch eliminated a similar polling delay in walsender already, the attached
>> patch does the same for walreceiver.
>>
>> After this patch, there is no unnecessary delays in the streaming
>> replication code path. Note that this is all still asynchronous, just with
>> reduced latency.
>>
>> This is pretty straightforward, but any comments?
>
> Is that supposed to be waiting 5000ms?

Yes, it gets interrupted as soon as WAL arrives, that timeout is to poll
for the standby trigger file to appear or SIGTERM.

BTW, I noticed that I missed incrementing the latch count in
win32_latch.c, and the owning/disowning the latch was done correctly,
you get an error if you restart the master and reconnect. I'll post an
updated patch shortly.

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