[patch 0/5] [PATCH CFT] more revlog experiments

[Eric Hopper]

On Mon, Mar 20, 2006 at 01:50:20PM -0600, Matt Mackall wrote:
> On Sat, Mar 18, 2006 at 07:05:31PM -0500, Chris Mason wrote:
> > Hello everyone,
> > 
> > Here's my latest set of revlog changes.  The index format has changed
> > slightly from the last time (sorry, repos from my last patch won't be
> > readable), and overall this one is faster.
> 
> This packing stuff is interesting, but I have some reservations.
> 
> Things that I've noticed:
> 
> a) breaks hg log foo.c (we no longer have file level indices)
> b) breaks hg debugindex .hg/data/foo.c.i (poking around at the
>    internals gets much harder)
> c) introduces an arbitrarily large multiplier (files per directory)
>    into all single file operations (like breaking a hardlink)
> d) adds a bunch of new complexity to be performant
> 
> Point (c) is the worst, and it means it's hard to consider this scheme
> as a default. And (d) means this will likely prove hard to maintain as
> an option.

I'm generally opposed to the packing changes since I think they add a
bunch of complexity to deal with issues that I consider to be things the
filesystem should be handling.

I think things like bdb, or this packing change add a lot of application
complexity, and reduce your ability to see your data in a satisfactory
way.  But they both exist largely to make up for filesystem deficiencies
like handling small files poorly, and not handling directories with a
lot of files in them very well either.

I would rather see these deficiencies exposed so that people working on
filesystems can fix them, because if they fix them, it makes it possible
for all applications to be a lot simpler and faster, and each individual
application does not have to invent its own solution

So, I think it might be useful to have as an option when performance is
very critical, I would rather it not be the default.  And if its deemed
so complex that it can't be supported as an option, I don't see why it
should be supported as a default.

Have fun if ata ll possible),
-- 
"It does me no injury for my neighbor to say there are twenty gods or no God.
It neither picks my pocket nor breaks my leg."  --- Thomas Jefferson
"Go to Heaven for the climate, Hell for the company."  -- Mark Twain
-- Eric Hopper (http://www.omnifarious.org/~hopper) --
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