Re: [PATCH 4/4] pack-bitmap: pass object filter to fill-in traversal

[Jeff King <peff@peff.net>]

On Wed, Apr 22, 2020 at 05:13:35PM -0600, Taylor Blau wrote:

> From: Jeff King <peff@peff.net>
> 
> Sometimes a bitmap traversal still has to walk some commits manually,
> because those commits aren't included in the bitmap packfile (e.g., due
> to a push or commit since the last full repack). If we're given an
> object filter, we don't pass it down to this traversal. It's not
> necessary for correctness because the bitmap code has its own filters to
> post-process the bitmap result (which it must, to filter out the objects
> that _are_ mentioned in the bitmapped packfile).
> 
> And with blob filters, there was no performance reason to pass along
> those filters, either. The fill-in traversal could omit them from the
> result, but it wouldn't save us any time to do so, since we'd still have
> to walk each tree entry to see if it's a blob or not.
> 
> But now that we support tree filters, there's opportunity for savings. A
> tree:depth=0 filter means we can avoid accessing trees entirely, since
> we know we won't them (or any of the subtrees or blobs they point to).

s/won't them/won't include them/ perhaps

> diff --git a/t/perf/p5310-pack-bitmaps.sh b/t/perf/p5310-pack-bitmaps.sh
> index b629a211f9..95379b1d4e 100755
> --- a/t/perf/p5310-pack-bitmaps.sh
> +++ b/t/perf/p5310-pack-bitmaps.sh
> @@ -95,4 +95,9 @@ test_perf 'pack to file (partial bitmap)' '
>  	git pack-objects --use-bitmap-index --all pack2b </dev/null >/dev/null
>  '
>  
> +test_perf 'rev-list with tree filter (partial bitmap)' '
> +	git rev-list --use-bitmap-index --count --objects --all \
> +		--filter=tree:0 >/dev/null
> +'

This covers perf testing of this partial-bitmap state, but we shoudl
make sure that we are covering correctness, too. I think so, because
t6113 creates a similar state for all of its tests.

-Peff