Re: Bluestore caching oddities, again

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On Sun, Aug 4, 2019 at 3:47 AM Christian Balzer <chibi@xxxxxxx> wrote:

> 2. Bluestore caching still broken
> When writing data with the fios below, it isn't cached on the OSDs.
> Worse, existing cached data that gets overwritten is removed from the
> cache, which while of course correct can't be free in terms of allocation
> overhead.
> Why not doing what any sensible person would expect from experience with
> any other cache there is, cache writes in case the data gets read again
> soon and in case of overwrites use existing allocations.

This is by design.
The BlueStore only populates its cache on reads, not on writes. The idea is
that a reasonable application does not read data it just wrote (and if it does
it's already cached at a higher layer like the page cache or a cache on the
hypervisor).



Paul
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