dirstate-tree: Avoid BTreeMap double-lookup when inserting a dirstate entry
The child nodes of a given node in the tree-shaped dirstate are kept in a
`BTreeMap` where keys are file names as strings. Finding or inserting a value
in the map takes `O(log(n))` string comparisons, which adds up when constructing
the tree.
The `entry` API allows finding a "spot" in the map that may or may not be
occupied and then access that value or insert a new one without doing map
lookup again. However the current API is limited in that calling `entry`
requires an owned key (and so a memory allocation), even if it ends up not
being used in the case where the map already has a value with an equal key.
This is still a win, with 4% better end-to-end time for `hg status` measured
here with hyperfine:
```
Benchmark #1: ../hg2/hg status -R $REPO --config=experimental.dirstate-tree.in-memory=1
Time (mean ± σ): 1.337 s ± 0.018 s [User: 892.9 ms, System: 437.5 ms]
Range (min … max): 1.316 s … 1.373 s 10 runs
Benchmark #2: ./hg status -R $REPO --config=experimental.dirstate-tree.in-memory=1
Time (mean ± σ): 1.291 s ± 0.008 s [User: 853.4 ms, System: 431.1 ms]
Range (min … max): 1.283 s … 1.309 s 10 runs
Summary
'./hg status -R $REPO --config=experimental.dirstate-tree.in-memory=1' ran
1.04 ± 0.02 times faster than '../hg2/hg status -R $REPO --config=experimental.dirstate-tree.in-memory=1'
```
* ./hg is this revision
* ../hg2/hg is its parent
* $REPO is an old snapshot of mozilla-central
Differential Revision: https://phab.mercurial-scm.org/D10550
#require no-windows
$ . "$TESTDIR/remotefilelog-library.sh"
$ hg init master
$ cd master
$ cat >> .hg/hgrc <<EOF
> [remotefilelog]
> server=True
> EOF
$ echo x > x
$ hg commit -qAm x
$ mkdir dir
$ echo y > dir/y
$ hg commit -qAm y
$ cd ..
Shallow clone from full
$ hgcloneshallow ssh://user@dummy/master shallow --noupdate
streaming all changes
2 files to transfer, 473 bytes of data
transferred 473 bytes in * seconds (*/sec) (glob)
searching for changes
no changes found
$ cd shallow
$ cat .hg/requires
dotencode
exp-remotefilelog-repo-req-1
fncache
generaldelta
persistent-nodemap (rust !)
revlog-compression-zstd (zstd !)
revlogv1
sparserevlog
store
$ hg update
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
2 files fetched over 1 fetches - (2 misses, 0.00% hit ratio) over *s (glob)
Log on a file without -f
$ hg log dir/y
warning: file log can be slow on large repos - use -f to speed it up
changeset: 1:2e73264fab97
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: y
Log on a file with -f
$ hg log -f dir/y
changeset: 1:2e73264fab97
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: y
Log on a file with kind in path
$ hg log -r "filelog('path:dir/y')"
changeset: 1:2e73264fab97
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: y
Log on multiple files with -f
$ hg log -f dir/y x
changeset: 1:2e73264fab97
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: y
changeset: 0:b292c1e3311f
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: x
Log on a directory
$ hg log dir
changeset: 1:2e73264fab97
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: y
Log on a file from inside a directory
$ cd dir
$ hg log y
warning: file log can be slow on large repos - use -f to speed it up
changeset: 1:2e73264fab97
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: y
Log on a file via -fr
$ cd ..
$ hg log -fr tip dir/ --template '{rev}\n'
1
Trace renames
$ hg mv x z
$ hg commit -m move
$ hg log -f z -T '{desc} {file_copies}\n' -G
@ move z (x)
:
o x
Verify remotefilelog handles rename metadata stripping when comparing file sizes
$ hg debugrebuilddirstate
$ hg status