view tests/test-completion.t @ 40326:fed697fa1734

sqlitestore: file storage backend using SQLite

This commit provides an extension which uses SQLite to store file
data (as opposed to revlogs).

As the inline documentation describes, there are still several
aspects to the extension that are incomplete. But it's a start.
The extension does support basic clone, checkout, and commit
workflows, which makes it suitable for simple use cases.

One notable missing feature is support for "bundlerepos." This is
probably responsible for the most test failures when the extension
is activated as part of the test suite.

All revision data is stored in SQLite. Data is stored as zstd
compressed chunks (default if zstd is available), zlib compressed
chunks (default if zstd is not available), or raw chunks (if
configured or if a compressed delta is not smaller than the raw
delta). This makes things very similar to revlogs.

Unlike revlogs, the extension doesn't yet enforce a limit on delta
chain length. This is an obvious limitation and should be addressed.
This is somewhat mitigated by the use of zstd, which is much faster
than zlib to decompress.

There is a dedicated table for storing deltas. Deltas are stored
by the SHA-1 hash of their uncompressed content. The "fileindex" table
has columns that reference the delta for each revision and the base
delta that delta should be applied against. A recursive SQL query
is used to resolve the delta chain along with the delta data.

By storing deltas by hash, we are able to de-duplicate delta storage!
With revlogs, the same deltas in different revlogs would result in
duplicate storage of that delta. In this scheme, inserting the
duplicate delta is a no-op and delta chains simply reference the
existing delta.

When initially implementing this extension, I did not have
content-indexed deltas and deltas could be duplicated across files
(just like revlogs). When I implemented content-indexed deltas, the
size of the SQLite database for a full clone of mozilla-unified
dropped:

before: 2,554,261,504 bytes
after:  2,488,754,176 bytes

Surprisingly, this is still larger than the bytes size of revlog
files:

revlog files: 2,104,861,230 bytes
du -b:        2,254,381,614

I would have expected storage to be smaller since we're not limiting
delta chain length and since we're using zstd instead of zlib. I
suspect the SQLite indexes and per-column overhead account for the
bulk of the differences. (Keep in mind that revlog uses a 64-byte
packed struct for revision index data and deltas are stored without
padding. Aside from the 12 unused bytes in the 32 byte node field,
revlogs are pretty efficient.) Another source of overhead is file
name storage. With revlogs, file names are stored in the filesystem.
But with SQLite, we need to store file names in the database. This is
roughly equivalent to the size of the fncache file, which for the
mozilla-unified repository is ~34MB.

Since the SQLite database isn't append-only and since delta chains
can reference any delta, this opens some interesting possibilities.
For example, we could store deltas in reverse, such that fulltexts
are stored for newer revisions and deltas are applied to reconstruct
older revisions. This is likely a more optimal storage strategy for
version control, as new data tends to be more frequently accessed
than old data. We would obviously need wire protocol support for
transferring revision data from newest to oldest. And we would
probably need some kind of mechanism for "re-encoding" stores. But
it should be doable.

This extension is very much experimental quality. There are a handful
of features that don't work. It probably isn't suitable for day-to-day
use. But it could be used in limited cases (e.g. read-only checkouts
like in CI). And it is also a good proving ground for alternate
storage backends. As we continue to define interfaces for all things
storage, it will be useful to have a viable alternate storage backend
to see how things shake out in practice.

test-storage.py passes on Python 2 and introduces no new test failures on
Python 3. Having the storage-level unit tests has proved to be insanely
useful when developing this extension. Those tests caught numerous bugs
during development and I'm convinced this style of testing is the way
forward for ensuring alternate storage backends work as intended. Of
course, test coverage isn't close to what it needs to be. But it is
a start. And what coverage we have gives me confidence that basic store
functionality is implemented properly.

Differential Revision: https://phab.mercurial-scm.org/D4928

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
  debugindexstats
  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
  addremove: similarity, subrepos, include, exclude, 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
  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
  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
  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
  debugindexstats: 
  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
  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
  files: rev, print0, include, exclude, template, subrepos
  forget: interactive, include, exclude, dry-run
  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
  init: ssh, remotecmd, insecure
  locate: rev, print0, fullpath, include, exclude
  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
  manifest: rev, all, template
  merge: force, rev, preview, abort, tool
  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
  pull: update, force, rev, bookmark, branch, ssh, remotecmd, insecure
  push: force, rev, bookmark, branch, new-branch, pushvars, ssh, remotecmd, insecure
  recover: 
  remove: after, force, subrepos, include, exclude, dry-run
  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: 
  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
  tag: force, local, rev, remove, edit, message, date, user
  tags: template
  tip: patch, git, style, template
  unbundle: update
  update: clean, check, merge, date, rev, tool
  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