Re: Reduced power consumption in WAL Writer process

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Jul 15, 2011, at 8:55 AM, Simon Riggs <simon(at)2ndQuadrant(dot)com> wrote:
>> The only difference is how bulk write operations are handled. As long
>> as we wake WALWriter before wal_buffers fills then we'll be good.
>> Wakeup once per wal buffer is too much. I agree we should measure this
>> to check how frequently wakeups are required for bulk ops.

> Yeah. The trick is to get the wake-ups to be frequent enough without adding too much latency to the backends that have to perform them. Off-hand, I don't have a good feeling for how hard that will be.

I'd say send the signal when wal buffers are more than X% full (maybe
half). The suggestion to send it when wrapping around at the end of the
array is not quite right, because that's an arbitrary condition that's
not related to how much work there is for the walwriter to do. It
should be cheap to check for this while advancing to a new wal buffer.

regards, tom lane