changegroup: introduce requests to define delta generation Currently, we iterate through each revision we will be producing a delta for then call into 1 of 2 functions for generating that delta. Deltas are emitted as we iterate. A problem with this model is that revision generation is tightly coupled to the changegroup code. And the storage layer needs to expose APIs like deltaparent() so changegroup delta generation can produce a delta with that knowledge. Another problem is that in this model, deltas can only be produced sequentially after the previous delta was produced and emitted. Some storage backends might be capable of producing deltas in parallel (e.g. if the changegroup deltas are cached somewhere). This commit aims to solve these problems by turning delta generation into a 2 phase implementation where the first phase determines info about all the deltas that need to be generated and the 2nd phase resolves those deltas. We introduce a "revisiondeltarequest" object that holds data about a to-be-generated delta. We perform a full pass over all revisions whose delta is to be generated and generate a "revisiondeltarequest" for each. Then we iterate over the "revisiondeltarequest" instances and derive a "revisiondelta" for each. This patch was quite large. In order to avoid even more churn, aspects of the implementation are less than ideal. e.g. we're recording revision numbers instead of nodes in a few places and we don't yet have a formal API for resolving an iterable of revisiondeltarequest instances. Things will be improved in subsequent commits. Unfortunately, this commit reduces performance substantially. For `hg perfchangegroupchangelog` on my hg repo: ! wall 1.512607 comb 1.510000 user 1.490000 sys 0.020000 (best of 7) ! wall 2.150863 comb 2.150000 user 2.150000 sys 0.000000 (best of 5) And for `hg bundle -t none-v2 -a` for the mozilla-unified repo: 178.32user 4.22system 3:02.59elapsed 190.97user 4.17system 3:15.19elapsed Some of this was attributed to changelog slowdown. `hg perfchangegroupchangelog` on mozilla-unified: ! wall 21.688715 comb 21.690000 user 21.570000 sys 0.120000 (best of 3) ! wall 25.683659 comb 25.680000 user 25.540000 sys 0.140000 (best of 3) Profiling seems to reveal that the changelog slowdown is due to reading changelog revisions multiple times. First in the linknode callback to resolve the set of files changed. Second in the delta generation. Before, we likely had hit the last revision cache in the revlog when doing delta generation since we performed that immediately after performing the linknode callback. I'm not exactly sure where the other ~8s are being spent. It might be from overhead of constructing a few million revisiondeltarequest objects. I'm OK with the regression for now because it is in service of a larger cause (storage abstraction). I'll try to profile later and claw back the performance. Differential Revision: https://phab.mercurial-scm.org/D4215

changegroup: refactor delta parent code We had recently abstracted the delta parent functions to facilitate extracting code from cgpacker. Now that we're in a better place, it is time to revisit the design. Changegroup version 1 requires that the previous node be used as the delta parent. Later versions allow any available node to be used as the base. In the case where an arbitrary parent can be used, the choice of a delta parent is best left in the hands of the storage backend. So it makes sense for the delta parent selection to be hidden away in the storage layer. This means deferring the choice of the delta parent selection function to as close to delta generation time as possible. This commit moves the delta selection logic to essentially just before delta generation. However, because changegroup version 1 limits what we can do, we have retained the ability to force a delta against the previous revision. As part of this, I realized that the ellipsis parent function was unused! That's because ellipsis mode always sends full revisions and not deltas. Differential Revision: https://phab.mercurial-scm.org/D4214

changegroup: differentiate between fulltext and diff based deltas Previously, revisiondelta encoded a delta and an optional prefix containing a delta header. The underlying code could populate the delta with either a real delta or a fulltext revision. Following the theme of wanting to defer serialization of revision data to the changegroup format as long as possible, it seems prudent for the revision delta instance to capture what type of data is being represented. This could possibly allow us to encode revision data differently in the future. But for the short term, it makes the behavior of a revisiondelta more explicit. Differential Revision: https://phab.mercurial-scm.org/D4213

changegroup: minor cleanups to deltagroup() Differential Revision: https://phab.mercurial-scm.org/D4212

changegroup: emit revisiondelta instances from deltagroup() By abstracting the concept of a delta group away from its serialization (the changegroup format), we make it easier to establish alternate serialization formats. We also make it possible to move aspects of delta group generation into the storage layer. This will allow storage to make decisions about e.g. delta parent choices without the changegroup code needing storage APIs to determine delta parents. We're still a bit of a way from there. Future commits will work towards that world. Differential Revision: https://phab.mercurial-scm.org/D4211

changegroup: move file chunk emission to generate() Same deal as manifests. We want to get to a point where we can emit data structures from deltagroup() and derive the raw changegroup data as late as possible. Differential Revision: https://phab.mercurial-scm.org/D4210

changegroup: move manifest chunk emission to generate() We want to get to a point where we can emit data structures from deltagroup() and derive the raw changegroup data as late as possible. Differential Revision: https://phab.mercurial-scm.org/D4209

changegroup: move size tracking and end of manifests to generate() Preparing for all the generate* functions to emit data structures instead of raw chunks. Differential Revision: https://phab.mercurial-scm.org/D4208

changegroup: emit delta group close chunk outside of deltagroup() I want to make deltagroup() emit data structures rather than serialized deltas. Upcoming commits will demonstrate why. Differential Revision: https://phab.mercurial-scm.org/D4207

changegroup: extract cgpacker.group() to standalone function It doesn't need to be part of the packer class. Differential Revision: https://phab.mercurial-scm.org/D4206

changegroup: pass all state into group() This will allow us to split it into a standalone function. Differential Revision: https://phab.mercurial-scm.org/D4205

changegroup: inline _prune() into call sites The functionality is pretty simple. As a bonus, _prune() had special code for the manifest case. We can now exclude this check from the file call site. Differential Revision: https://phab.mercurial-scm.org/D4199

changegroup: inline _packmanifests() into generatemanifests() It is relatively small. Every other generate*() calls group() directly. So the new code is consistent. Differential Revision: https://phab.mercurial-scm.org/D4198

changegroup: invert conditional and dedent I don't like seeing code that visually resembles the pyramid of doom. Differential Revision: https://phab.mercurial-scm.org/D4197

changegroup: make _revisiondeltanarrow() a standalone function It doesn't require any state on the packer. Everything impacting behavior is passed in as a function. So split it out, just like what was done for _revisiondeltanormal(). Differential Revision: https://phab.mercurial-scm.org/D4196

changegroup: pass state into _revisiondeltanarrow After this, the method no longer accesses self and can be split into a standalone function. Differential Revision: https://phab.mercurial-scm.org/D4195

changegroup: inline _close() Now that it doesn't clear self._clrevtolocalrev on every invocation and is a simple one-liner that calls another function, we can do away with this method and inline its content into all call sites. Differential Revision: https://phab.mercurial-scm.org/D4194

changegroup: pass clrevtolocalrev to each group clrevtolocalrev is a per-changegroup group mapping revisions to aid with shallow clone. Back when this functionality was implemented in an extension, this dict was added to the packer instance so monkeypatched functions could reference it there. Now that this code is part of core, we can pass the dict to each consumer properly so it doesn't have to live on the cgpacker instance. This commit does that. Differential Revision: https://phab.mercurial-scm.org/D4193

changegroup: combine _generatefiles() into generatefiles() These were split out in a06aab274aef as part of moving the narrow code into core. They don't need to be separate functions. Differential Revision: https://phab.mercurial-scm.org/D4192

changegroup: define linknodes callbacks in generatefiles() This is how it is done everywhere else. But the logic here is a bit more complex because shallow clone needs to reference the original linknode implementation. But at least now all function implementations are defined in the same place. Differential Revision: https://phab.mercurial-scm.org/D4191

changegroup: track changelog to manifest revision map explicitly Previously, self._nextclrevtolocalrev was only populated as part of the changelog lookup callback. But cgpacker._close() was looking at self._nextclrevtolocalrev on every invocation. Since self._nextclrevtolocalrev is for communicating the mapping of changelog revisions to manifest revisions, this commit refactors the code to make that explicit. The changelog state now stores this mapping. And after the changelog group is emitted, we update self._clrevtolocalrev with that dict. self._nextclrevtolocalrev is unused and has been deleted. Differential Revision: https://phab.mercurial-scm.org/D4190

changegroup: remove _clnodetorev cgpacker._clnodetorev is a glorified cache/index of changelog nodes to revision numbers. I'm not sure why it exists. Maybe performance? But its presence is making refactoring of this code more complicated than it needs to be. This commit removes the cache and replaces it with direct lookups against the changelog. If this cache was for performance reasons, we should be able to restore it easily enough... after the changegroup refactor is complete. Differential Revision: https://phab.mercurial-scm.org/D4189

changegroup: rename _fullnodes to _fullclnodes So it is obvious which nodes we are talking about. And sneak in a docs change to reflect that this variable is a set. Differential Revision: https://phab.mercurial-scm.org/D4188

changegroup: move part of _revisiondeltanarrow into group() Now all the logic for determining which delta generation code is called lives in a single function. Differential Revision: https://phab.mercurial-scm.org/D4187