The WAL (and walls in general) impose a performance overhead. If one were to just take a machine out of the cluster, permanently, when a machine crashes, you could quickly get all the shards back up to N replicas after a node crashes.
So realistically, running with a WAL is somewhat redundant. ESPECIALLY when you have 2 data centers at 3 replicas in each datacenter (for a total of 6 replicas). I think this would only be about a 15% performance overhead. Additionally, on flash, if you lay out the SSTables properly, you arguably don’t need a WAL because your SSTable itself can be a wall and you could run without memtables. This has been proposed in a number of situations. Especially on something like FusionIO … Thoughts? -- Founder/CEO Spinn3r.com Location: *San Francisco, CA* blog: http://burtonator.wordpress.com … or check out my Google+ profile <https://plus.google.com/102718274791889610666/posts> <http://spinn3r.com>
