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From: Kent Overstreet <kent.overstreet@linux.dev>
To: Martin Steigerwald <martin@lichtvoll.de>
Cc: linux-bcachefs@vger.kernel.org
Subject: Re: Questions related to BCacheFS
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On Sun, Nov 19, 2023 at 12:15:19AM +0100, Martin Steigerwald wrote:
> Thanks again, Kent.
> 
> Kent Overstreet - 18.11.23, 22:07:27 CET:
> > > As far as I understand one specific performance related aspect of
> > > BCacheFS would be low latencies due to the frontend / backend
> > > architecture which in principle is based on what has been there in
> > > BCache already. I am intending to explore a bit into that concept in
> > > my article.
> > 
> > The low latency stuff actually wasn't in bcache - that work came later.
> 
> So the frontend / backend architecture is not that much of what makes 
> BCacheFS unique? Important to know as it seems I may have misunderstood 
> something here.

The "filesystem on top of a database" is the main thing that makes
bcachefs unique - you have that right.

bcache had much of the core btree design - log structured btree nodes
with eytzinger search trees; that's how we got a high enough performance
btree to make the "filesystem on top of a database" thing practical.

But the btree in bcache was, from a performance POV, prototype quality -
stable, but a lot of performance corner cases unfinished.

The latency work, real iterators, and the whole transaction layer came
later :)