streamclone: use backgroundfilecloser (
issue4889)
Closing files that have been appended to is slow on Windows/NTFS.
CloseHandle() calls on this platform often take 1-10ms - and that's
on my i7-6700K Skylake processor with a modern and fast SSD. Contrast
with other I/O operations, such as writing data, which take <100us.
This means that creating/appending thousands of files can add
significant overhead. For example, cloning mozilla-central creates
~232,000 revlog files. Assuming 1ms per CloseHandle(), that yields
232s (3:52) of wall time waiting for file closes!
The impact of this overhead can be measured most directly when applying
stream clone bundles. Applying these files is effectively uncompressing
a tar archive (read: it's very fast).
Using a RAM disk (read: no I/O wait), the difference in wall time for a
`hg debugapplystreamclonebundle` for a ~1731 MB mozilla-central bundle
between Windows and Linux from the same machine is drastic:
Linux: ~12.8s (128MB/s)
Windows: ~352.0s (4.7MB/s)
Windows is ~27.5x slower. Yikes!
After this patch:
Linux: ~12.8s (128MB/s)
Windows: ~102.1s (16.1MB/s)
Windows is now ~3.4x faster. Unfortunately, it is still ~8x slower than
Linux. Profiling reveals a few hot code paths that could likely be
improved. But those are for other patches.
This patch introduces test-clone-uncompressed.t because existing tests
of `clone --uncompressed` are scattered about and adding a variation for
background thread closing to e.g. test-http.t doesn't feel correct.
Mercurial for Plan 9 from Bell Labs
===================================
This directory contains support for Mercurial on Plan 9 from Bell Labs
platforms. It is assumed that the version of Python running on these
systems supports the ANSI/POSIX Environment (APE). At the time of this
writing, the bichued/python port is the most commonly installed version
of Python on these platforms. If a native port of Python is ever made,
some minor modification will need to be made to support some of the more
esoteric requirements of the platform rather than those currently made
(cf. posix.py).
By default, installations will have the factotum extension enabled; this
extension permits factotum(4) to act as an authentication agent for
HTTP repositories. Additionally, an extdiff command named 9diff is
enabled which generates diff(1) compatible output suitable for use with
the plumber(4).
Commit messages are plumbed using E if no editor is defined; users must
update the plumbed file to continue, otherwise the hg process must be
interrupted.
Some work remains with regard to documentation. Section 5 manual page
references for hgignore and hgrc need to be re-numbered to section 6 (file
formats) and a new man page writer should be written to support the
Plan 9 man macro set. Until these issues can be resolved, manual pages
are elided from the installation.
Basic install:
% mk install # do a system-wide install
% hg debuginstall # sanity-check setup
% hg # see help
A proto(2) file is included in this directory as an example of how a
binary distribution could be packaged, ostensibly with contrib(1).
See https://mercurial-scm.org/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.