Re: [PATCH] midx.c: clear auxiliary MIDX files first

[Taylor Blau <me@ttaylorr.com>]

On Wed, Oct 26, 2022 at 09:31:28AM -0400, Derrick Stolee wrote:
> On 10/26/22 1:41 AM, Jeff King wrote:
> > On Tue, Oct 25, 2022 at 02:25:20PM -0400, Taylor Blau wrote:
> >
> >> Since they were added in c528e17966 (pack-bitmap: write multi-pack
> >> bitmaps, 2021-08-31), the routine to remove MIDXs removed the
> >> multi-pack-index file itself before removing its associated .bitmap and
> >> .rev file(s), if any.
> >>
> >> This creates a window where a MIDX's .bitmap file exists without its
> >> corresponding MIDX. If a reader tries to load a MIDX bitmap during that
> >> time, they will get a warning, and the MIDX bitmap code will gracefully
> >> degrade.
> >>
> >> Remove this window entirely by removing the MIDX last, and removing its
> >> auxiliary files first.
> >
> > We remove that window, but don't we create a new one where a reader may
> > see the midx but not the bitmap? That won't generate a warning (it just
> > looks like a midx that never had a bitmap generated), but it will cause
> > the reader to follow the slow, non-bitmap path.
>
> Yes, this is the worrisome direction. The midx is read first, then that
> points to the .bitmap file (based on its trailing hash). If the midx isn't
> there, then the .bitmap will not be read.

Yes, thinking on it more I agree with this and (the elided) analysis
below.

Let's drop this one. Thanks, both!


Thanks,
Taylor