dirstate: Remove the flat Rust DirstateMap implementation
Before this changeset we had two Rust implementations of `DirstateMap`.
This removes the "flat" DirstateMap so that the "tree" DirstateMap is always
used when Rust enabled. This simplifies the code a lot, and will enable
(in the next changeset) further removal of a trait abstraction.
This is a performance regression when:
* Rust is enabled, and
* The repository uses the legacy dirstate-v1 file format, and
* For `hg status`, unknown files are not listed (such as with `-mard`)
The regression is about 100 milliseconds for `hg status -mard` on a
semi-large repository (mozilla-central), from ~320ms to ~420ms.
We deem this to be small enough to be worth it.
The new dirstate-v2 is still experimental at this point, but we aim to
stabilize it (though not yet enable it by default for new repositories)
in Mercurial 6.0. Eventually, upgrating repositories to dirsate-v2 will
eliminate this regression (and enable other performance improvements).
# Background
The flat DirstateMap was introduced with the first Rust implementation of the
status algorithm. It works similarly to the previous Python + C one, with a
single `HashMap` that associates file paths to a `DirstateEntry` (where Python
has a dict).
We later added the tree DirstateMap where the root of the tree contains nodes
for files and directories that are directly at the root of the repository,
and nodes for directories can contain child nodes representing the files and
directly that *they* contain directly. The shape of this tree mirrors that of
the working directory in the filesystem. This enables the status algorithm to
traverse this tree in tandem with traversing the filesystem tree, which in
turns enables a more efficient algorithm.
Furthermore, the new dirstate-v2 file format is also based on a tree of the
same shape. The tree DirstateMap can access a dirstate-v2 file without parsing
it: binary data in a single large (possibly memory-mapped) bytes buffer is
traversed on demand. This allows `DirstateMap` creation to take `O(1)` time.
(Mutation works by creating new in-memory nodes with copy-on-write semantics,
and serialization is append-mostly.)
The tradeoff is that for "legacy" repositories that use the dirstate-v1 file
format, parsing that file into a tree DirstateMap takes more time. Profiling
shows that this time is dominated by `HashMap`. For a dirstate containing `F`
files with an average `D` directory depth, the flat DirstateMap does parsing
in `O(F)` number of HashMap operations but the tree DirstateMap in `O(F × D)`
operations, since each node has its own HashMap containing its child nodes.
This slower costs ~140ms on an old snapshot of mozilla-central, and ~80ms
on an old snapshot of the Netbeans repository.
The status algorithm is faster, but with `-mard` (when not listing unknown
files) it is typically not faster *enough* to compensate the slower parsing.
Both Rust implementations are always faster than the Python + C implementation
# Benchmark results
All benchmarks are run on changeset 98c0408324e6, with repositories that use
the dirstate-v1 file format, on a server with 4 CPU cores and 4 CPU threads
(no HyperThreading).
`hg status` benchmarks show wall clock times of the entire command as the
average and standard deviation of serveral runs, collected by
https://github.com/sharkdp/hyperfine and reformated.
Parsing benchmarks are wall clock time of the Rust function that converts a
bytes buffer of the dirstate file into the `DirstateMap` data structure as
used by the status algorithm. A single run each, collected by running
`hg status` this environment variable:
RUST_LOG=hg::dirstate::dirstate_map=trace,hg::dirstate_tree::dirstate_map=trace
Benchmark 1: Rust flat DirstateMap → Rust tree DirstateMap
hg status
mozilla-clean 562.3 ms ± 2.0 ms → 462.5 ms ± 0.6 ms 1.22 ± 0.00 times faster
mozilla-dirty 859.6 ms ± 2.2 ms → 719.5 ms ± 3.2 ms 1.19 ± 0.01 times faster
mozilla-ignored 558.2 ms ± 3.0 ms → 457.9 ms ± 2.9 ms 1.22 ± 0.01 times faster
mozilla-unknowns 859.4 ms ± 5.7 ms → 716.0 ms ± 4.7 ms 1.20 ± 0.01 times faster
netbeans-clean 336.5 ms ± 0.9 ms → 339.5 ms ± 0.4 ms 0.99 ± 0.00 times faster
netbeans-dirty 491.4 ms ± 1.6 ms → 475.1 ms ± 1.2 ms 1.03 ± 0.00 times faster
netbeans-ignored 343.7 ms ± 1.0 ms → 347.8 ms ± 0.4 ms 0.99 ± 0.00 times faster
netbeans-unknowns 484.3 ms ± 1.0 ms → 466.0 ms ± 1.2 ms 1.04 ± 0.00 times faster
hg status -mard
mozilla-clean 317.3 ms ± 0.6 ms → 422.5 ms ± 1.2 ms 0.75 ± 0.00 times faster
mozilla-dirty 315.4 ms ± 0.6 ms → 417.7 ms ± 1.1 ms 0.76 ± 0.00 times faster
mozilla-ignored 314.6 ms ± 0.6 ms → 417.4 ms ± 1.0 ms 0.75 ± 0.00 times faster
mozilla-unknowns 312.9 ms ± 0.9 ms → 417.3 ms ± 1.6 ms 0.75 ± 0.00 times faster
netbeans-clean 212.0 ms ± 0.6 ms → 283.6 ms ± 0.8 ms 0.75 ± 0.00 times faster
netbeans-dirty 211.4 ms ± 1.0 ms → 283.4 ms ± 1.6 ms 0.75 ± 0.01 times faster
netbeans-ignored 211.4 ms ± 0.9 ms → 283.9 ms ± 0.8 ms 0.74 ± 0.01 times faster
netbeans-unknowns 211.1 ms ± 0.6 ms → 283.4 ms ± 1.0 ms 0.74 ± 0.00 times faster
Parsing
mozilla-clean 38.4ms → 177.6ms
mozilla-dirty 38.8ms → 177.0ms
mozilla-ignored 38.8ms → 178.0ms
mozilla-unknowns 38.7ms → 176.9ms
netbeans-clean 16.5ms → 97.3ms
netbeans-dirty 16.5ms → 98.4ms
netbeans-ignored 16.9ms → 97.4ms
netbeans-unknowns 16.9ms → 96.3ms
Benchmark 2: Python + C dirstatemap → Rust tree DirstateMap
hg status
mozilla-clean 1261.0 ms ± 3.6 ms → 461.1 ms ± 0.5 ms 2.73 ± 0.00 times faster
mozilla-dirty 2293.4 ms ± 9.1 ms → 719.6 ms ± 3.6 ms 3.19 ± 0.01 times faster
mozilla-ignored 1240.4 ms ± 2.3 ms → 457.7 ms ± 1.9 ms 2.71 ± 0.00 times faster
mozilla-unknowns 2283.3 ms ± 9.0 ms → 719.7 ms ± 3.8 ms 3.17 ± 0.01 times faster
netbeans-clean 879.7 ms ± 3.5 ms → 339.9 ms ± 0.5 ms 2.59 ± 0.00 times faster
netbeans-dirty 1257.3 ms ± 4.7 ms → 474.6 ms ± 1.6 ms 2.65 ± 0.01 times faster
netbeans-ignored 943.9 ms ± 1.9 ms → 347.3 ms ± 1.1 ms 2.72 ± 0.00 times faster
netbeans-unknowns 1188.1 ms ± 5.0 ms → 465.2 ms ± 2.3 ms 2.55 ± 0.01 times faster
hg status -mard
mozilla-clean 903.2 ms ± 3.6 ms → 423.4 ms ± 2.2 ms 2.13 ± 0.01 times faster
mozilla-dirty 884.6 ms ± 4.5 ms → 417.3 ms ± 1.4 ms 2.12 ± 0.01 times faster
mozilla-ignored 881.9 ms ± 1.3 ms → 417.3 ms ± 0.8 ms 2.11 ± 0.00 times faster
mozilla-unknowns 878.5 ms ± 1.9 ms → 416.4 ms ± 0.9 ms 2.11 ± 0.00 times faster
netbeans-clean 434.9 ms ± 1.8 ms → 284.0 ms ± 0.8 ms 1.53 ± 0.01 times faster
netbeans-dirty 434.1 ms ± 0.8 ms → 283.1 ms ± 0.8 ms 1.53 ± 0.00 times faster
netbeans-ignored 431.7 ms ± 1.1 ms → 283.6 ms ± 1.8 ms 1.52 ± 0.01 times faster
netbeans-unknowns 433.0 ms ± 1.3 ms → 283.5 ms ± 0.7 ms 1.53 ± 0.00 times faster
Differential Revision: https://phab.mercurial-scm.org/D11516
#testcases dirstate-v1 dirstate-v2
#if dirstate-v2
#require rust
$ echo '[format]' >> $HGRCPATH
$ echo 'exp-dirstate-v2=1' >> $HGRCPATH
#endif
init
$ hg init t
$ cd t
setup
$ echo r1 > r1
$ hg ci -qAmr1 -d'0 0'
$ mkdir directory
$ echo r2 > directory/r2
$ hg ci -qAmr2 -d'1 0'
$ echo 'ignored' > .hgignore
$ hg ci -qAmr3 -d'2 0'
purge without the extension
$ hg st
$ touch foo
$ hg purge
permanently delete 1 unkown files? (yN) n
abort: removal cancelled
[250]
$ hg st
? foo
$ hg purge --no-confirm
$ hg st
now enabling the extension
$ cat <<EOF >> $HGRCPATH
> [extensions]
> purge =
> EOF
delete an empty directory
$ mkdir empty_dir
$ hg purge -p -v
empty_dir
$ hg purge --confirm
permanently delete at least 1 empty directories? (yN) n
abort: removal cancelled
[250]
$ hg purge -v
removing directory empty_dir
$ ls -A
.hg
.hgignore
directory
r1
delete an untracked directory
$ mkdir untracked_dir
$ touch untracked_dir/untracked_file1
$ touch untracked_dir/untracked_file2
$ hg purge -p
untracked_dir/untracked_file1
untracked_dir/untracked_file2
$ hg purge -v
removing file untracked_dir/untracked_file1
removing file untracked_dir/untracked_file2
removing directory untracked_dir
$ ls -A
.hg
.hgignore
directory
r1
delete an untracked file
$ touch untracked_file
$ touch untracked_file_readonly
$ "$PYTHON" <<EOF
> import os
> import stat
> f = 'untracked_file_readonly'
> os.chmod(f, stat.S_IMODE(os.stat(f).st_mode) & ~stat.S_IWRITE)
> EOF
$ hg purge -p
untracked_file
untracked_file_readonly
$ hg purge --confirm
permanently delete 2 unkown files? (yN) n
abort: removal cancelled
[250]
$ hg purge -v
removing file untracked_file
removing file untracked_file_readonly
$ ls -A
.hg
.hgignore
directory
r1
delete an untracked file in a tracked directory
$ touch directory/untracked_file
$ hg purge -p
directory/untracked_file
$ hg purge -v
removing file directory/untracked_file
$ ls -A
.hg
.hgignore
directory
r1
delete nested directories
$ mkdir -p untracked_directory/nested_directory
$ hg purge -p
untracked_directory/nested_directory
$ hg purge -v
removing directory untracked_directory/nested_directory
removing directory untracked_directory
$ ls -A
.hg
.hgignore
directory
r1
delete nested directories from a subdir
$ mkdir -p untracked_directory/nested_directory
$ cd directory
$ hg purge -p
untracked_directory/nested_directory
$ hg purge -v
removing directory untracked_directory/nested_directory
removing directory untracked_directory
$ cd ..
$ ls -A
.hg
.hgignore
directory
r1
delete only part of the tree
$ mkdir -p untracked_directory/nested_directory
$ touch directory/untracked_file
$ cd directory
$ hg purge -p ../untracked_directory
untracked_directory/nested_directory
$ hg purge --confirm
permanently delete 1 unkown files? (yN) n
abort: removal cancelled
[250]
$ hg purge -v ../untracked_directory
removing directory untracked_directory/nested_directory
removing directory untracked_directory
$ cd ..
$ ls -A
.hg
.hgignore
directory
r1
$ ls directory/untracked_file
directory/untracked_file
$ rm directory/untracked_file
skip ignored files if -i or --all not specified
$ touch ignored
$ hg purge -p
$ hg purge --confirm
$ hg purge -v
$ touch untracked_file
$ ls
directory
ignored
r1
untracked_file
$ hg purge -p -i
ignored
$ hg purge --confirm -i
permanently delete 1 ignored files? (yN) n
abort: removal cancelled
[250]
$ hg purge -v -i
removing file ignored
$ ls -A
.hg
.hgignore
directory
r1
untracked_file
$ touch ignored
$ hg purge -p --all
ignored
untracked_file
$ hg purge --confirm --all
permanently delete 1 unkown and 1 ignored files? (yN) n
abort: removal cancelled
[250]
$ hg purge -v --all
removing file ignored
removing file untracked_file
$ ls
directory
r1
abort with missing files until we support name mangling filesystems
$ touch untracked_file
$ rm r1
hide error messages to avoid changing the output when the text changes
$ hg purge -p 2> /dev/null
untracked_file
$ hg st
! r1
? untracked_file
$ hg purge -p
untracked_file
$ hg purge -v 2> /dev/null
removing file untracked_file
$ hg st
! r1
$ hg purge -v
$ hg revert --all --quiet
$ hg st -a
tracked file in ignored directory (issue621)
$ echo directory >> .hgignore
$ hg ci -m 'ignore directory'
$ touch untracked_file
$ hg purge -p
untracked_file
$ hg purge -v
removing file untracked_file
skip excluded files
$ touch excluded_file
$ hg purge -p -X excluded_file
$ hg purge -v -X excluded_file
$ ls -A
.hg
.hgignore
directory
excluded_file
r1
$ rm excluded_file
skip files in excluded dirs
$ mkdir excluded_dir
$ touch excluded_dir/file
$ hg purge -p -X excluded_dir
$ hg purge -v -X excluded_dir
$ ls -A
.hg
.hgignore
directory
excluded_dir
r1
$ ls excluded_dir
file
$ rm -R excluded_dir
skip excluded empty dirs
$ mkdir excluded_dir
$ hg purge -p -X excluded_dir
$ hg purge -v -X excluded_dir
$ ls -A
.hg
.hgignore
directory
excluded_dir
r1
$ rmdir excluded_dir
skip patterns
$ mkdir .svn
$ touch .svn/foo
$ mkdir directory/.svn
$ touch directory/.svn/foo
$ hg purge -p -X .svn -X '*/.svn'
$ hg purge -p -X re:.*.svn
$ rm -R .svn directory r1
only remove files
$ mkdir -p empty_dir dir
$ touch untracked_file dir/untracked_file
$ hg purge -p --files
dir/untracked_file
untracked_file
$ hg purge -v --files
removing file dir/untracked_file
removing file untracked_file
$ ls -A
.hg
.hgignore
dir
empty_dir
$ ls dir
only remove dirs
$ mkdir -p empty_dir dir
$ touch untracked_file dir/untracked_file
$ hg purge -p --dirs
empty_dir
$ hg purge -v --dirs
removing directory empty_dir
$ ls -A
.hg
.hgignore
dir
untracked_file
$ ls dir
untracked_file
remove both files and dirs
$ mkdir -p empty_dir dir
$ touch untracked_file dir/untracked_file
$ hg purge -p --files --dirs
dir/untracked_file
untracked_file
empty_dir
$ hg purge -v --files --dirs
removing file dir/untracked_file
removing file untracked_file
removing directory empty_dir
removing directory dir
$ ls -A
.hg
.hgignore
$ cd ..