compression: introduce a `storage.revlog.zlib.level` configuration This option control the zlib compression level used when compression revlog chunk. This is also a good excuse to pave the way for a similar configuration option for the zstd compression engine. Having a dedicated option for each compression algorithm is useful because they don't support the same range of values. Using a higher zlib compression impact CPU consumption at compression time, but does not directly affected decompression time. However dealing with small compressed chunk can directly help decompression and indirectly help other revlog logic. I ran some basic test on repositories using different level. I am using the mercurial, pypy, netbeans and mozilla-central clone from our benchmark suite. All tested repository use sparse-revlog and got all their delta recomputed. The different compression level has a small effect on the repository size (about 10% variation in the total range). My quick analysis is that revlog mostly store small delta, that are not affected by the compression level much. So the variation probably mostly comes from better compression of the snapshots revisions, and snapshot revision only represent a small portion of the repository content. I also made some basic timings measurements. The "read" timings are gathered using simple run of `hg perfrevlogrevisions`, the "write" timings using `hg perfrevlogwrite` (restricted to the last 5000 revisions for netbeans and mozilla central). The timings are gathered on a generic machine, (not one of our performance locked machine), so small variation might not be meaningful. However large trend remains relevant. Keep in mind that these numbers are not pure compression/decompression time. They also involve the full revlog logic. In particular the difference in chunk size has an impact on the delta chain structure, affecting performance when writing or reading them. On read/write performance, the compression level has a bigger impact. Counter-intuitively, the higher compression levels improve "write" performance for the large repositories in our tested setting. Maybe because the last 5000 delta chain end up having a very different shape in this specific spot? Or maybe because of a more general trend of better delta chains thanks to the smaller chunk and snapshot. This series does not intend to change the default compression level. However, these result call for a deeper analysis of this performance difference in the future. Full data ========= repo level .hg/store size 00manifest.d read write ---------------------------------------------------------------- mercurial 1 49,402,813 5,963,475 0.170159 53.250304 mercurial 6 47,197,397 5,875,730 0.182820 56.264320 mercurial 9 47,121,596 5,849,781 0.189219 56.293612 pypy 1 370,830,572 28,462,425 2.679217 460.721984 pypy 6 340,112,317 27,648,747 2.768691 467.537158 pypy 9 338,360,736 27,639,003 2.763495 476.589918 netbeans 1 1,281,847,810 165,495,457 122.477027 520.560316 netbeans 6 1,205,284,353 159,161,207 139.876147 715.930400 netbeans 9 1,197,135,671 155,034,586 141.620281 678.297064 mozilla 1 2,775,497,186 298,527,987 147.867662 751.263721 mozilla 6 2,596,856,420 286,597,671 170.572118 987.056093 mozilla 9 2,587,542,494 287,018,264 163.622338 739.803002

compression: accept level management for zlib compression We update the zlib related class to be support setting the compression level. This changeset focus on updating the internal only. A way to configure this level will be introduced in the next changeset.

util: extract compression code in `mercurial.utils.compression` The code seems large enough to be worth extracting. This is similar to what was done for various module in `mercurial/utils/`. Since None of the compression logic takes a `ui` objet, issuing deprecation warning is tricky. Luckly the logic does not seems to have many external users.

merge: make "labels" argument to graft() optional, like it is for update() graft() just passes the argument on to update(), and update() doesn't require it, so graft() shouldn't either. Differential Revision: https://phab.mercurial-scm.org/D6175

revset: remove comment about linkrev workaround from user-facing docs I think the code is clear enough so we don't need to keep the comment at all (by now, most Mercurial developers are probably familiar with the linkrevs issues). Differential Revision: https://phab.mercurial-scm.org/D6176

shelve: let cmdutil.revert() take care of backing up untracked files cmdutil.revert() backs up untracked files, so I don't see a reason to do it shelve.mergefiles(). We have tests for this and they still pass. Differential Revision: https://phab.mercurial-scm.org/D6174

shelve: stop passing list of files to revert It seems to work just fine to not specify any files here. I suspect it looked the way it did for historical reasons. It apparently used to use merge instead of rebase until 1d7a36ff2615 (shelve: use rebase instead of merge (issue4068), 2013-10-23) and it makes sense to want to restrict the set of files then. I noticed this because of the files.extend(shelvectx.p1().files()). If the working copy was clean before, then shelvectx.p1() will be the working copy parent and that ended up adding all the files in that set. In our Google-internal Mercurial setup (including a FUSE) that was very noticeably slow when the working copy parent happened to have many files in large directories. This patch doesn't yet remove the call to shelvectx.p1().files(). We also use that set for deciding what to back up. I'm pretty sure it's safe to back up only the set of files we already back even if we no longer restrict the set of files to revert, so this patch should be safe on its own. Regardless, the next patch will delegate the backing-up to cmdutil.revert(). Incidentally, this also gets rid of a repo.pathto() that I had earlier wanted to get rid of. Differential Revision: https://phab.mercurial-scm.org/D6173

remotefilelog: prefetch files in deterministic order I have been troubleshooting some slowness in this area (it's unclear if it's the client or server that's to blame, but that's beside the point) and it's a lot easier to do troubleshoot if the files are prefetched in the same order each time. Differential Revision: https://phab.mercurial-scm.org/D6172

debugdiscovery: display time elapsed during the discovery step This is a useful information. Now that we perform more analysing after the discovery is done, it is worth have a more precise measurement. For serious timing analysis use `hg perfdiscovery`.

debugdiscovery: only list common heads on verbose The list of common heads is only part of the useful information. In addition on repository with many heads, the information is very not helpful (just fill a couple of screen with hash). As a result we hide it behind a --verbose flag.