Mercurial > hg
view mercurial/help/environment.txt @ 26379:39d643252b9f
revlog: use existing file handle when reading during _addrevision
_addrevision() may need to read from revlogs as part of computing
deltas. Previously, we would flush existing file handles and open
a new, short-lived file handle to perform the reading.
If we have an existing file handle, it seems logical to reuse it
for reading instead of opening a new file handle. This patch
makes that the new behavior.
After this patch, revlog files are only reopened when adding
revisions if the revlog is switched from inline to non-inline.
On Linux when unbundling a bundle of the mozilla-central repo, this
patch has the following impact on system call counts:
Call Before After Delta
write 827,639 673,390 -154,249
open 700,103 684,089 -16,014
read 74,489 74,489 0
fstat 493,924 461,896 -32,028
close 249,131 233,117 -16,014
stat 242,001 242,001 0
lstat 18,676 18,676 0
lseek 20,268 20,268 0
ioctl 14,652 13,173 -1,479
TOTAL 3,180,758 2,930,679 -250,079
It's worth noting that many of the open() calls fail due to missing
files. That's why there are many more open() calls than close().
Despite the significant system call reduction, this change does not
seem to have a significant performance impact on Linux.
On Windows 10 (not a VM, on a SSD), this patch appears to reduce
unbundle time for mozilla-central from ~960s to ~920s. This isn't
as significant as I was hoping. But a decrease it is nonetheless.
Still, Windows unbundle performance is still >2x slower than Linux.
Despite the lack of significant gains, fewer system calls is fewer
system calls. If nothing else, this will narrow the focus of potential
areas to optimize in the future.
author | Gregory Szorc <gregory.szorc@gmail.com> |
---|---|
date | Sun, 27 Sep 2015 16:08:18 -0700 |
parents | 9f97de157aad |
children | a9ed5a8fc5e0 |
line wrap: on
line source
HG Path to the 'hg' executable, automatically passed when running hooks, extensions or external tools. If unset or empty, this is the hg executable's name if it's frozen, or an executable named 'hg' (with %PATHEXT% [defaulting to COM/EXE/BAT/CMD] extensions on Windows) is searched. HGEDITOR This is the name of the editor to run when committing. See EDITOR. (deprecated, use configuration file) HGENCODING This overrides the default locale setting detected by Mercurial. This setting is used to convert data including usernames, changeset descriptions, tag names, and branches. This setting can be overridden with the --encoding command-line option. HGENCODINGMODE This sets Mercurial's behavior for handling unknown characters while transcoding user input. The default is "strict", which causes Mercurial to abort if it can't map a character. Other settings include "replace", which replaces unknown characters, and "ignore", which drops them. This setting can be overridden with the --encodingmode command-line option. HGENCODINGAMBIGUOUS This sets Mercurial's behavior for handling characters with "ambiguous" widths like accented Latin characters with East Asian fonts. By default, Mercurial assumes ambiguous characters are narrow, set this variable to "wide" if such characters cause formatting problems. HGMERGE An executable to use for resolving merge conflicts. The program will be executed with three arguments: local file, remote file, ancestor file. (deprecated, use configuration file) HGRCPATH A list of files or directories to search for configuration files. Item separator is ":" on Unix, ";" on Windows. If HGRCPATH is not set, platform default search path is used. If empty, only the .hg/hgrc from the current repository is read. For each element in HGRCPATH: - if it's a directory, all files ending with .rc are added - otherwise, the file itself will be added HGPLAIN When set, this disables any configuration settings that might change Mercurial's default output. This includes encoding, defaults, verbose mode, debug mode, quiet mode, tracebacks, and localization. This can be useful when scripting against Mercurial in the face of existing user configuration. Equivalent options set via command line flags or environment variables are not overridden. HGPLAINEXCEPT This is a comma-separated list of features to preserve when HGPLAIN is enabled. Currently the only value supported is "i18n", which preserves internationalization in plain mode. Setting HGPLAINEXCEPT to anything (even an empty string) will enable plain mode. HGUSER This is the string used as the author of a commit. If not set, available values will be considered in this order: - HGUSER (deprecated) - configuration files from the HGRCPATH - EMAIL - interactive prompt - LOGNAME (with ``@hostname`` appended) (deprecated, use configuration file) EMAIL May be used as the author of a commit; see HGUSER. LOGNAME May be used as the author of a commit; see HGUSER. VISUAL This is the name of the editor to use when committing. See EDITOR. EDITOR Sometimes Mercurial needs to open a text file in an editor for a user to modify, for example when writing commit messages. The editor it uses is determined by looking at the environment variables HGEDITOR, VISUAL and EDITOR, in that order. The first non-empty one is chosen. If all of them are empty, the editor defaults to 'vi'. PYTHONPATH This is used by Python to find imported modules and may need to be set appropriately if this Mercurial is not installed system-wide.