On 4/28/2014 1:04 PM, Heikki Linnakangas wrote:
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.)On 04/28/2014 06:47 PM, Karl Denninger wrote:What I am curious about, however, is the xlog -- that appears to suffer pretty badly from 128k record size, although it compresses even more-materially; 1.94x (!) The files in the xlog directory are large (16MB each) and thus "first blush" would be that having a larger record size for that storage area would help. It appears that instead it hurts.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.- Heikki
Isn't WAL essentially sequential writes during normal operation? -- -- Karl karl@xxxxxxxxxxxxx
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