view tests/test-pathconflicts-basic.t @ 34824:e2ad93bcc084

revlog: introduce an experimental flag to slice chunks reads when too sparse

Delta chains can become quite sparse if there is a lot of unrelated data between
relevant pieces. Right now, revlog always reads all the necessary data for the
delta chain in one single read. This can lead to a lot of unrelated data to be
read (see issue5482 for more details).
One can use the `experimental.maxdeltachainspan` option with a large value
(or -1) to easily produce a very sparse delta chain.

This change introduces the ability to slice the chunks retrieval into  multiple
reads, skipping large sections of unrelated data. Preliminary testing shows
interesting results. For example the peak memory consumption to read a manifest
on a large repository is reduced from 600MB to 250MB (200MB without
maxdeltachainspan). However, the slicing itself and the multiple reads can have
an negative impact on performance. This is why the new feature is hidden behind
an experimental flag.

Future changesets will add various parameters to control the slicing heuristics.
We hope to experiment a wide variety of repositories during 4.4 and hopefully
turn the feature on by default in 4.5.
As a first try, the algorithm itself is prone to deep changes. However, we wish
to define APIs and have a baseline to work on.

  $ hg init repo
  $ cd repo
  $ echo base > base
  $ hg add base
  $ hg commit -m "base"
  $ hg bookmark -i base
  $ echo 1 > a
  $ hg add a
  $ hg commit -m "file"
  $ hg bookmark -i file
  $ echo 2 > a
  $ hg commit -m "file2"
  $ hg bookmark -i file2
  $ hg up -q 0
  $ mkdir a
  $ echo 2 > a/b
  $ hg add a/b
  $ hg commit -m "dir"
  created new head
  $ hg bookmark -i dir

Basic merge - local file conflicts with remote directory

  $ hg up -q file
  $ hg bookmark -i
  $ hg merge --verbose dir
  resolving manifests
  a: path conflict - a file or link has the same name as a directory
  the local file has been renamed to a~853701544ac3
  resolve manually then use 'hg resolve --mark a'
  moving a to a~853701544ac3
  getting a/b
  1 files updated, 0 files merged, 0 files removed, 1 files unresolved
  use 'hg resolve' to retry unresolved file merges or 'hg update -C .' to abandon
  [1]
  $ hg update --clean .
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ rm a~853701544ac3

Basic update - local directory conflicts with remote file

  $ hg up -q 0
  $ mkdir a
  $ echo 3 > a/b
  $ hg up file
  a: untracked directory conflicts with file
  abort: untracked files in working directory differ from files in requested revision
  [255]
  $ hg up --clean file
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (activating bookmark file)

Repo state is ok

  $ hg sum
  parent: 1:853701544ac3 
   file
  branch: default
  bookmarks: *file
  commit: (clean)
  update: 2 new changesets (update)
  phases: 4 draft

Basic update - untracked file conflicts with remote directory

  $ hg up -q 0
  $ echo untracked > a
  $ hg up --config merge.checkunknown=warn dir
  a: replacing untracked file
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (activating bookmark dir)
  $ cat a.orig
  untracked
  $ rm -f a.orig

Basic clean update - local directory conflicts with changed remote file

  $ hg up -q file
  $ rm a
  $ mkdir a
  $ echo 4 > a/b
  $ hg up file2
  abort: *: '$TESTTMP/repo/a' (glob)
  [255]
  $ hg up --clean file2
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (activating bookmark file2)

Repo state is ok

  $ hg sum
  parent: 2:f64e09fac717 
   file2
  branch: default
  bookmarks: *file2
  commit: (clean)
  update: 1 new changesets, 2 branch heads (merge)
  phases: 4 draft