Comment 1 for bug 406686

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Robert Collins wrote:
> Public bug reported:
>
> StreamSource.get_stream_for_missing_keys does not include inventory CHK
> pages. It needs to otherwise when a stacked repo asks for adjacent
> inventories to permit deltas, the inventories won't be complete enough
> to permit deltas. Currently we speculatively include this data from the
> client in get_stream.
>
> ** Affects: bzr
> Importance: Undecided
> Status: New
>

So I'll mention that at least in original testing this wasn't needed.

We send:
 1) The minimal chk pages based on a delta comparison
 2) When we need fallback inventories we send *all possible referenced*
pages from the parent inventories.

As an example, say you have a CHK layout of

root1 => [leaf1, leaf2] # rev1
root2 => [leaf1, leaf3] # rev2

Then for the "get_stream()" we would send

root2, leaf3

and then get_stream_for_missing_keys, we would request #rev1-complete
and send

root1 => [leaf1, leaf2]

I wasn't able to find a way that those two combined wouldn't send
everything referenced from root2 (either it changed and we sent it, or
it didn't change and it is contained in the parent's full reference.)

If you can find a way that this isn't true, we can absolutely
re-evaluate it.

And I agree that the generic StreamSource should always be correct.
(Perhaps this is where the issue is?)

Andrew removed the code path to do CHK => CHK fetching because it had a
trivial bug in it, which made it clear it wasn't being called *by the
test suite*.

My current understanding is we want to get inventory delta streaming
working, and then we don't send CHK pages anyway in the generic code
path. So spending too much time here may not be worthwhile.

John
=:->
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