Re: BlueStore bitmap allocator under Luminous and Mimic

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Hi Wido,

the main driver for this backport were multiple complains on write ops latency increasing over time.

E.g. see thread named:  "ceph osd commit latency increase over time, until restart" here.

Or http://tracker.ceph.com/issues/38738

Most symptoms showed Stupid Allocator as a root cause for that.

Hence we've got a decision to backport bitmap allocator which should work a fix/workaround.


Thanks,

Igor


On 4/15/2019 3:39 PM, Wido den Hollander wrote:
Hi,

With the release of 12.2.12 the bitmap allocator for BlueStore is now
available under Mimic and Luminous.

[osd]
bluestore_allocator = bitmap
bluefs_allocator = bitmap

Before setting this in production: What might the implications be and
what should be thought of?

 From what I've read the bitmap allocator seems to be better in read
performance and uses less memory.

In Nautilus bitmap is the default, but L and M still default to stupid.

Since the bitmap allocator was backported there must be a use-case to
use the bitmap allocator instead of stupid.

Thanks!

Wido
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