On Sun, Aug 14, 2022 at 10:32:12PM -0700, Junio C Hamano wrote: > > We're in the middle of walking through the entries of a tree object via > > process_tree_contents(). We see a blob (or it could even be another tree > > entry) that we don't have, so we call is_promisor_object() to check it. > > That function loops over all of the objects in the promisor packfile, > > including the tree we're currently walking. > > I forgot that the above "loops over" happens only once to populate > the oidset hashtable, and briefly wondered if we are being grossly > inefficient by scanning pack .idx file each time we encounter a > missing object. "Upon first call, that function loops over > ... walking, to prepare a hashtable to answer if any object id is > referred to by an object in promisor packs" would have helped ;-). Right. When you have worked in an area, sometimes it is easy to forget which things are common knowledge and which are not. :) I don't mind at all if you want to amend the commit message as you apply. > > It may also be a good direction for this function in general, as there > > are other possible optimizations that rely on doing some analysis before > > parsing: > > > > - we could detect blobs and avoid reading their contents; they can't > > link to other objects, but parse_object() doesn't know that we don't > > care about checking their hashes. > > > > - we could avoid allocating object structs entirely for most objects > > (since we really only need them in the oidset), which would save > > some memory. > > > > - promisor commits could use the commit-graph rather than loading the > > object from disk > > > > This commit doesn't do any of those optimizations, but I think it argues > > that this direction is reasonable, rather than relying on parse_object() > > and trying to teach it to give us more information about whether it > > parsed. > > Yeah, all of the future bits sound sensible. I very intentionally didn't work on those things yet, because I wanted to make sure we got a simple fix in as quickly as possible. That said, I don't have immediate plans for them. They are perhaps not quite small enough for #leftoverbits, but I think they might also be nice bite-sized chunks for somebody wanting to get their feet wet in that part of the code. -Peff
