Re: Cost limited statements RFC

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
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