On 3/12/19 8:40 AM, vitalif@xxxxxxxxxx wrote:
One way or another we can only have a single thread sending writes to
rocksdb. A lot of the prior optimization work on the write side was
to get as much processing out of the kv_sync_thread as possible.
That's still a worthwhile goal as it's typically what bottlenecks with
high amounts of concurrency. What I think would be very interesting
though is if we moved more toward a model where we had lots shards
(OSDs or shards of an OSD) with independent rocksdb instances and less
threading overhead per shard. That's the way the seastar work is
going, and also sort of the model I've been thinking about for a very
simple single-threaded OSD.
Doesn't rocksdb have pipelined writes? Isn't it better to just use
that builtin concurrency instead of factoring in your own?
Pipelined writes were added in rocksdb 5.5.1 back in the summer of
2017. That wasn't available when bluestore was being written. We may be
able to make use of it now but I don't think anyone has taken the time
to figure out how much work it would take or what kind of benefit we
would get.
Mark
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