On 4/28/2014 1:22 PM, Heikki Linnakangas wrote:
On 04/28/2014 09:07 PM, Karl Denninger wrote:The WAL is fsync'd frequently. My guess is that that causes a lot of extra work to repeatedly recompress the same data, or something like that.It shouldn't as ZFS re-writes on change, and what's showing up is not high I/O*count* but rather percentage-busy, which implies lots of head movement (that is, lots of sub-allocation unit writes.)That sounds consistent frequent fsyncs.Isn't WAL essentially sequential writes during normal operation?Yes, it's totally sequential. But it's fsync'd at every commit, which means a lot of small writes.- Heikki
Makes sense; I'll muse on whether there's a way to optimize this further... I'm not running into performance problems at present but I'd rather be ahead of it....
-- -- Karl karl@xxxxxxxxxxxxx
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