tests/test-completion.t

changegroup: remove reordering control (BC)

This logic - including the experimental bundle.reorder option -
was originally added in a8e3931e3fb5 in 2011 and then later ported
to changegroup.py.

The intent of this option and associated logic is to control
the ordering of revisions in deltagroups in changegroups. At the
time it was implemented, only changegroup version 1 existed
and generaldelta revlogs were just coming into the world. Changegroup
version 1 requires that deltas be made against the last revision
sent over the wire. Used with generaldelta, this created an
impedance mismatch of sorts and resulted in changegroup producers
spending a lot of time recomputing deltas.

Revision reordering was introduced so outgoing revisions would be
sent in "generaldelta order" and producers would be able to
reuse internal deltas from storage.

Later on, we introduced changegroup version 2. It supported denoting
which revision a delta was against. So we no longer needed to
sort outgoing revisions to ensure optimal delta generation from the
producer. So, subsequent changegroup versions disabled reordering.

We also later made the changelog not store deltas by default. And
we also made the changelog send out deltas in storage order. Why we
do this for changelog, I'm not sure. Maybe we want to preserve revision
order across clones? It doesn't really matter for this commit.

Fast forward to 2018. We want to abstract storage backends. And having
changegroup code require knowledge about how deltas are stored
internally interferes with that goal.

This commit removes reordering control from changegroup generation.
After this commit, the reordering behavior is:

* The changelog is always sent out in storage order (no behavior
  change).
* Non-changelog generaldelta revlogs are reordered to always be in DAG
  topological order (previously, generaldelta revlogs would be emitted
  in storage order for version 2 and 3 changegroups).
* Non-changelog non-generaldelta revlogs are sent in storage order (no
  behavior change).
* There exists no config option to override behavior.

The big difference here is that generaldelta revlogs now *always* have
their revisions sorted in DAG order before going out over the wire. This
behavior was previously only done for changegroup version 1. Version 2
and version 3 changegroups disabled reordering because the interchange
format supported encoding arbitrary delta parents, so reordering wasn't
strictly necessary.

I can think of a few significant implications for this change.

Because changegroup receivers will now see non-changelog revisions
in DAG order instead of storage order, the internal storage order of
manifests and files may differ substantially between producer and
consumer. I don't think this matters that much, since the storage
order of manifests and files is largely hidden from users. Only
the storage order of changelog matters (because `hg log` shows the
changelog in storage order). I don't think there should be any
controversy here.

The reordering of revisions has implications for changegroup producers.
Previously, generaldelta revlogs would be emitted in storage order.
And in the common case, the internally-stored delta could effectively
be copied from disk into the deltagroup delta. This meant that emitting
delta groups for generaldelta revlogs would be mostly linear read I/O.
This is desirable for performance. With us now reordering generaldelta
revlog revisions in DAG order, the read operations may use more random
I/O instead of sequential I/O. This could result in performance
loss. But with the prevalence of SSDs and fast random I/O, I'm not
too worried. (Note: the optimal emission order for revlogs is actually
delta encoding order. But the changegroup code wasn't doing that before
or after this change. We could potentially implement that in a later
commit.)

Changegroups in DAG order will have implications for receivers.
Previously, receiving storage order might mean seeing a number of
interleaved branches. This would mean long delta chains, sparse
I/O, and possibly more fulltext revisions instead of deltas, blowing
up storage storage. (This is the same set of problems that sparse
revlogs aims to address.) With the producer now sending revisions in DAG
order, the receiver also stores revisions in DAG order. That means
revisions for the same DAG branch are all grouped together. And this
should yield better storage outcomes. In other words, sending the
reordered changegroup allows the receiver to have better storage
order and for the producer to not propagate its (possibly sub-optimal)
internal storage order.

On the mozilla-unified repository, this change influences bundle
generation:

$ hg bundle -t none-v2 -a
before: time: real 355.680 secs (user 256.790+0.000 sys 16.820+0.000)
after:  time: real 382.950 secs (user 281.700+0.000 sys 17.690+0.000)

before: 7,150,228,967 bytes (uncompressed)
after:  7,041,556,273 bytes (uncompressed)

before: 1,669,063,234 bytes (zstd l=3)
after:  1,628,598,830 bytes (zstd l=3)

$ hg unbundle
before: time: real 511.910 secs (user 466.750+0.000 sys 32.680+0.000)
after:  time: real 487.790 secs (user 443.940+0.000 sys 30.840+0.000)

00manifest.d size:
source: 274,924,292 bytes
before: 304,741,626 bytes
after:  245,252,087 bytes

.hg/store total file size:
source: 2,649,133,490
before: 2,680,888,130
after:  2,627,875,673

We see the bundle size drop. That's probably because if a revlog
internally isn't storing a delta, it will choose to delta against
the last emitted revision. And on repos with interleaved branches
(like mozilla-unified), the previous revision could be an unrelated
branch and therefore be a large delta. But with this patch, the
previous revision is likely p1 or p2 and a delta should be small.

We also see the manifest size drop by ~50 MB. It's worth noting that
the manifest actually *increased* in size by ~25 MB in the old
strategy and decreased ~25 MB from its source in the new strategy.
Again, my explanation for this is that the DAG ordering in the
changegroup is resulting in better grouping of revisions in the
receiver, which results in more compact delta chains and higher
storage efficiency.

Unbundle time also dropped. I suspect this is due to the revlog having
to work less to compute deltas since the incoming deltas are more
optimal. i.e. the receiver spends less time resolving fulltext
revisions as incoming deltas bounce around between DAG branches and
delta chains.

We also see bundle generation time increase. This is not desirable.
However, the regression is only significant on the original repository:
if we generate a bundle from the repository created from the new,
always reordered bundles, we're close to baseline (if not at it with
expected noise):

$ hg bundle -t none-v2 -a
before (original): time: real 355.680 secs (user 256.790+0.000 sys 16.820+0.000)
after (original):  time: real 382.950 secs (user 281.700+0.000 sys 17.690+0.000)
after (new repo):  time: real 362.280 secs (user 260.300+0.000 sys 17.700+0.000)

This regression is a bit worrying because it will impact serving
canonical repositories (that don't have optimal internal storage
unless they are reordered - possibly as part of running
`hg debugupgraderepo`). However, this regression will only be
noticed by very large changegroups. And I'm guessing/hoping that
any repository that large is using clonebundles to mitigate server
load.

Again, sending DAG order isn't the optimal send order for servers:
sending in storage-delta order is. But in order to enable
storage-optimal send order, we'll need a storage API that handles
sorting. Future commits will introduce such an API.

Differential Revision: https://phab.mercurial-scm.org/D4721

Show all commands except debug commands
  $ hg debugcomplete
  add
  addremove
  annotate
  archive
  backout
  bisect
  bookmarks
  branch
  branches
  bundle
  cat
  clone
  commit
  config
  copy
  diff
  export
  files
  forget
  graft
  grep
  heads
  help
  identify
  import
  incoming
  init
  locate
  log
  manifest
  merge
  outgoing
  parents
  paths
  phase
  pull
  push
  recover
  remove
  rename
  resolve
  revert
  rollback
  root
  serve
  status
  summary
  tag
  tags
  tip
  unbundle
  update
  verify
  version

Show all commands that start with "a"
  $ hg debugcomplete a
  add
  addremove
  annotate
  archive

Do not show debug commands if there are other candidates
  $ hg debugcomplete d
  diff

Show debug commands if there are no other candidates
  $ hg debugcomplete debug
  debugancestor
  debugapplystreamclonebundle
  debugbuilddag
  debugbundle
  debugcapabilities
  debugcheckstate
  debugcolor
  debugcommands
  debugcomplete
  debugconfig
  debugcreatestreamclonebundle
  debugdag
  debugdata
  debugdate
  debugdeltachain
  debugdirstate
  debugdiscovery
  debugdownload
  debugextensions
  debugfileset
  debugformat
  debugfsinfo
  debuggetbundle
  debugignore
  debugindex
  debugindexdot
  debuginstall
  debugknown
  debuglabelcomplete
  debuglocks
  debugmanifestfulltextcache
  debugmergestate
  debugnamecomplete
  debugobsolete
  debugpathcomplete
  debugpeer
  debugpickmergetool
  debugpushkey
  debugpvec
  debugrebuilddirstate
  debugrebuildfncache
  debugrename
  debugrevlog
  debugrevlogindex
  debugrevspec
  debugserve
  debugsetparents
  debugssl
  debugsub
  debugsuccessorssets
  debugtemplate
  debuguigetpass
  debuguiprompt
  debugupdatecaches
  debugupgraderepo
  debugwalk
  debugwhyunstable
  debugwireargs
  debugwireproto

Do not show the alias of a debug command if there are other candidates
(this should hide rawcommit)
  $ hg debugcomplete r
  recover
  remove
  rename
  resolve
  revert
  rollback
  root
Show the alias of a debug command if there are no other candidates
  $ hg debugcomplete rawc
  

Show the global options
  $ hg debugcomplete --options | sort
  --color
  --config
  --cwd
  --debug
  --debugger
  --encoding
  --encodingmode
  --help
  --hidden
  --noninteractive
  --pager
  --profile
  --quiet
  --repository
  --time
  --traceback
  --verbose
  --version
  -R
  -h
  -q
  -v
  -y

Show the options for the "serve" command
  $ hg debugcomplete --options serve | sort
  --accesslog
  --address
  --certificate
  --cmdserver
  --color
  --config
  --cwd
  --daemon
  --daemon-postexec
  --debug
  --debugger
  --encoding
  --encodingmode
  --errorlog
  --help
  --hidden
  --ipv6
  --name
  --noninteractive
  --pager
  --pid-file
  --port
  --prefix
  --print-url
  --profile
  --quiet
  --repository
  --stdio
  --style
  --subrepos
  --templates
  --time
  --traceback
  --verbose
  --version
  --web-conf
  -6
  -A
  -E
  -R
  -S
  -a
  -d
  -h
  -n
  -p
  -q
  -t
  -v
  -y

Show an error if we use --options with an ambiguous abbreviation
  $ hg debugcomplete --options s
  hg: command 's' is ambiguous:
      serve showconfig status summary
  [255]

Show all commands + options
  $ hg debugcommands
  add: include, exclude, subrepos, dry-run
  annotate: rev, follow, no-follow, text, user, file, date, number, changeset, line-number, skip, ignore-all-space, ignore-space-change, ignore-blank-lines, ignore-space-at-eol, include, exclude, template
  clone: noupdate, updaterev, rev, branch, pull, uncompressed, stream, ssh, remotecmd, insecure
  commit: addremove, close-branch, amend, secret, edit, interactive, include, exclude, message, logfile, date, user, subrepos
  diff: rev, change, text, git, binary, nodates, noprefix, show-function, reverse, ignore-all-space, ignore-space-change, ignore-blank-lines, ignore-space-at-eol, unified, stat, root, include, exclude, subrepos
  export: bookmark, output, switch-parent, rev, text, git, binary, nodates, template
  forget: interactive, include, exclude, dry-run
  init: ssh, remotecmd, insecure
  log: follow, follow-first, date, copies, keyword, rev, line-range, removed, only-merges, user, only-branch, branch, prune, patch, git, limit, no-merges, stat, graph, style, template, include, exclude
  merge: force, rev, preview, abort, tool
  pull: update, force, rev, bookmark, branch, ssh, remotecmd, insecure
  push: force, rev, bookmark, branch, new-branch, pushvars, ssh, remotecmd, insecure
  remove: after, force, subrepos, include, exclude, dry-run
  serve: accesslog, daemon, daemon-postexec, errorlog, port, address, prefix, name, web-conf, webdir-conf, pid-file, stdio, cmdserver, templates, style, ipv6, certificate, print-url, subrepos
  status: all, modified, added, removed, deleted, clean, unknown, ignored, no-status, terse, copies, print0, rev, change, include, exclude, subrepos, template
  summary: remote
  update: clean, check, merge, date, rev, tool
  addremove: similarity, subrepos, include, exclude, dry-run
  archive: no-decode, prefix, rev, type, subrepos, include, exclude
  backout: merge, commit, no-commit, parent, rev, edit, tool, include, exclude, message, logfile, date, user
  bisect: reset, good, bad, skip, extend, command, noupdate
  bookmarks: force, rev, delete, rename, inactive, list, template
  branch: force, clean, rev
  branches: active, closed, template
  bundle: force, rev, branch, base, all, type, ssh, remotecmd, insecure
  cat: output, rev, decode, include, exclude, template
  config: untrusted, edit, local, global, template
  copy: after, force, include, exclude, dry-run
  debugancestor: 
  debugapplystreamclonebundle: 
  debugbuilddag: mergeable-file, overwritten-file, new-file
  debugbundle: all, part-type, spec
  debugcapabilities: 
  debugcheckstate: 
  debugcolor: style
  debugcommands: 
  debugcomplete: options
  debugcreatestreamclonebundle: 
  debugdag: tags, branches, dots, spaces
  debugdata: changelog, manifest, dir
  debugdate: extended
  debugdeltachain: changelog, manifest, dir, template
  debugdirstate: nodates, dates, datesort
  debugdiscovery: old, nonheads, rev, ssh, remotecmd, insecure
  debugdownload: output
  debugextensions: template
  debugfileset: rev, all-files, show-matcher, show-stage
  debugformat: template
  debugfsinfo: 
  debuggetbundle: head, common, type
  debugignore: 
  debugindex: changelog, manifest, dir, template
  debugindexdot: changelog, manifest, dir
  debuginstall: template
  debugknown: 
  debuglabelcomplete: 
  debuglocks: force-lock, force-wlock, set-lock, set-wlock
  debugmanifestfulltextcache: clear, add
  debugmergestate: 
  debugnamecomplete: 
  debugobsolete: flags, record-parents, rev, exclusive, index, delete, date, user, template
  debugpathcomplete: full, normal, added, removed
  debugpeer: 
  debugpickmergetool: rev, changedelete, include, exclude, tool
  debugpushkey: 
  debugpvec: 
  debugrebuilddirstate: rev, minimal
  debugrebuildfncache: 
  debugrename: rev
  debugrevlog: changelog, manifest, dir, dump
  debugrevlogindex: changelog, manifest, dir, format
  debugrevspec: optimize, show-revs, show-set, show-stage, no-optimized, verify-optimized
  debugserve: sshstdio, logiofd, logiofile
  debugsetparents: 
  debugssl: 
  debugsub: rev
  debugsuccessorssets: closest
  debugtemplate: rev, define
  debuguigetpass: prompt
  debuguiprompt: prompt
  debugupdatecaches: 
  debugupgraderepo: optimize, run
  debugwalk: include, exclude
  debugwhyunstable: 
  debugwireargs: three, four, five, ssh, remotecmd, insecure
  debugwireproto: localssh, peer, noreadstderr, nologhandshake, ssh, remotecmd, insecure
  files: rev, print0, include, exclude, template, subrepos
  graft: rev, continue, stop, abort, edit, log, no-commit, force, currentdate, currentuser, date, user, tool, dry-run
  grep: print0, all, diff, text, follow, ignore-case, files-with-matches, line-number, rev, all-files, user, date, template, include, exclude
  heads: rev, topo, active, closed, style, template
  help: extension, command, keyword, system
  identify: rev, num, id, branch, tags, bookmarks, ssh, remotecmd, insecure, template
  import: strip, base, edit, force, no-commit, bypass, partial, exact, prefix, import-branch, message, logfile, date, user, similarity
  incoming: force, newest-first, bundle, rev, bookmarks, branch, patch, git, limit, no-merges, stat, graph, style, template, ssh, remotecmd, insecure, subrepos
  locate: rev, print0, fullpath, include, exclude
  manifest: rev, all, template
  outgoing: force, rev, newest-first, bookmarks, branch, patch, git, limit, no-merges, stat, graph, style, template, ssh, remotecmd, insecure, subrepos
  parents: rev, style, template
  paths: template
  phase: public, draft, secret, force, rev
  recover: 
  rename: after, force, include, exclude, dry-run
  resolve: all, list, mark, unmark, no-status, re-merge, tool, include, exclude, template
  revert: all, date, rev, no-backup, interactive, include, exclude, dry-run
  rollback: dry-run, force
  root: 
  tag: force, local, rev, remove, edit, message, date, user
  tags: template
  tip: patch, git, style, template
  unbundle: update
  verify: 
  version: template

  $ hg init a
  $ cd a
  $ echo fee > fee
  $ hg ci -q -Amfee
  $ hg tag fee
  $ mkdir fie
  $ echo dead > fie/dead
  $ echo live > fie/live
  $ hg bookmark fo
  $ hg branch -q fie
  $ hg ci -q -Amfie
  $ echo fo > fo
  $ hg branch -qf default
  $ hg ci -q -Amfo
  $ echo Fum > Fum
  $ hg ci -q -AmFum
  $ hg bookmark Fum

Test debugpathcomplete

  $ hg debugpathcomplete f
  fee
  fie
  fo
  $ hg debugpathcomplete -f f
  fee
  fie/dead
  fie/live
  fo

  $ hg rm Fum
  $ hg debugpathcomplete -r F
  Fum

Test debugnamecomplete

  $ hg debugnamecomplete
  Fum
  default
  fee
  fie
  fo
  tip
  $ hg debugnamecomplete f
  fee
  fie
  fo

Test debuglabelcomplete, a deprecated name for debugnamecomplete that is still
used for completions in some shells.

  $ hg debuglabelcomplete
  Fum
  default
  fee
  fie
  fo
  tip
  $ hg debuglabelcomplete f
  fee
  fie
  fo