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.
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