On 6/8/13 4:43 PM, Jeff Janes wrote:
> Also, in all the anecdotes I've been hearing about autovacuum causing
> problems from too much IO, in which people can identify the specific
> problem, it has always been the write pressure, not the read, that
> caused the problem. Should the default be to have the read limit be
> inactive and rely on the dirty-limit to do the throttling?
That would be bad, I have to carefully constrain both of them on systems
that are short on I/O throughput. There all sorts of cases where
cleanup of a large and badly cached relation will hit the read limit
right now.
I suspect the reason we don't see as many complaints is that a lot more
systems can handle 7.8MB/s of random reads then there are ones that can
do 3.9MB/s of random writes. If we removed that read limit, a lot more
complaints would start rolling in about the read side.
--
Greg Smith 2ndQuadrant US greg@2ndQuadrant.com Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support www.2ndQuadrant.com