Re: Allow a per-tablespace effective_io_concurrency setting

On Fri, Sep  4, 2015 at 05:21:38PM +0100, Greg Stark wrote:
> Wouldn't SSDs need much *less* aggressive prefetching? There's still
> latency and there are multiple I/O channels so they will still need
> some. But spinning media gives latencies measured in milliseconds. You
> can process a lot of tuples in milliseconds. If you have a hundred
> spindles you want them all busy doing seeks because in the 5ms it
> takes them to do that you can proess all the results on a single cpu
> and the rest of time is spend waiting.
> 
> When your media has latency on the order of microseconds then you only
> need to have a small handful of I/O requests in flight to keep your
> processor busy.

Well, there is still the processing time of getting that data ready. 
All I know is that people have reported that prefetching is even more
useful for SSDs.

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http://enterprisedb.com
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