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2017-07-12gc: run pre-detach operations under lockLibravatar Jeff King1-0/+21
We normally try to avoid having two auto-gc operations run at the same time, because it wastes resources. This was done long ago in 64a99eb47 (gc: reject if another gc is running, unless --force is given, 2013-08-08). When we do a detached auto-gc, we run the ref-related commands _before_ detaching, to avoid confusing lock contention. This was done by 62aad1849 (gc --auto: do not lock refs in the background, 2014-05-25). These two features do not interact well. The pre-detach operations are run before we check the gc.pid lock, meaning that on a busy repository we may run many of them concurrently. Ideally we'd take the lock before spawning any operations, and hold it for the duration of the program. This is tricky, though, with the way the pid-file interacts with the daemonize() process. Other processes will check that the pid recorded in the pid-file still exists. But detaching causes us to fork and continue running under a new pid. So if we take the lock before detaching, the pid-file will have a bogus pid in it. We'd have to go back and update it with the new pid after detaching. We'd also have to play some tricks with the tempfile subsystem to tweak the "owner" field, so that the parent process does not clean it up on exit, but the child process does. Instead, we can do something a bit simpler: take the lock only for the duration of the pre-detach work, then detach, then take it again for the post-detach work. Technically, this means that the post-detach lock could lose to another process doing pre-detach work. But in the long run this works out. That second process would then follow-up by doing post-detach work. Unless it was in turn blocked by a third process doing pre-detach work, and so on. This could in theory go on indefinitely, as the pre-detach work does not repack, and so need_to_gc() will continue to trigger. But in each round we are racing between the pre- and post-detach locks. Eventually, one of the post-detach locks will win the race and complete the full gc. So in the worst case, we may racily repeat the pre-detach work, but we would never do so simultaneously (it would happen via a sequence of serialized race-wins). Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-04-16t6500: wait for detached auto gc at the end of the test scriptLibravatar SZEDER Gábor1-1/+17
The last test in 't6500-gc', 'background auto gc does not run if gc.log is present and recent but does if it is old', added in a831c06a2 (gc: ignore old gc.log files, 2017-02-10), may sporadically trigger an error message from the test harness: rm: cannot remove 'trash directory.t6500-gc/.git/objects': Directory not empty The test in question ends with executing an auto gc in the backround, which occasionally takes so long that it's still running when 'test_done' is about to remove the trash directory. This 'rm -rf $trash' in the foreground might race with the detached auto gc to create and delete files and directories, and gc might (re-)create a path that 'rm' already visited and removed, triggering the above error message when 'rm' attempts to remove its parent directory. Commit bb05510e5 (t5510: run auto-gc in the foreground, 2016-05-01) fixed the same problem in a different test script by simply disallowing background gc. Unfortunately, what worked there is not applicable here, because the purpose of this test is to check the behavior of a detached auto gc. Make sure that the test doesn't continue before the gc is finished in the background with a clever bit of shell trickery: - Open fd 9 in the shell, to be inherited by the background gc process, because our daemonize() only closes the standard fds 0, 1 and 2. - Duplicate this fd 9 to stdout. - Read 'git gc's stdout, and thus fd 9, through a command substitution. We don't actually care about gc's output, but this construct has two useful properties: - This read blocks until stdout or fd 9 are open. While stdout is closed after the main gc process creates the background process and exits, fd 9 remains open until the backround process exits. - The variable assignment from the command substitution gets its exit status from the command executed within the command substitution, i.e. a failing main gc process will cause the test to fail. Note, that this fd trickery doesn't work on Windows, because due to MSYS limitations the git process only inherits the standard fds 0, 1 and 2 from the shell. Luckily, it doesn't matter in this case, because on Windows daemonize() is basically a noop, thus 'git gc --auto' always runs in the foreground. And since we can now continue the test reliably after the detached gc finished, check that there is only a single packfile left at the end, i.e. that the detached gc actually did what it was supposed to do. Also add a comment at the end of the test script to warn developers of future tests about this issue of long running detached gc processes. Helped-by: Jeff King <peff@peff.net> Helped-by: Johannes Sixt <j6t@kdbg.org> Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-02-13gc: ignore old gc.log filesLibravatar David Turner1-0/+15
A server can end up in a state where there are lots of unreferenced loose objects (say, because many users are doing a bunch of rebasing and pushing their rebased branches). Running "git gc --auto" in this state would cause a gc.log file to be created, preventing future auto gcs, causing pack files to pile up. Since many git operations are O(n) in the number of pack files, this would lead to poor performance. Git should never get itself into a state where it refuses to do any maintenance, just because at some point some piece of the maintenance didn't make progress. Teach Git to ignore gc.log files which are older than (by default) one day old, which can be tweaked via the gc.logExpiry configuration variable. That way, these pack files will get cleaned up, if necessary, at least once per day. And operators who find a need for more-frequent gcs can adjust gc.logExpiry to meet their needs. There is also some cleanup: a successful manual gc, or a warning-free auto gc with an old log file, will remove any old gc.log files. It might still happen that manual intervention is required (e.g. because the repo is corrupt), but at the very least it won't be because Git is too dumb to try again. Signed-off-by: David Turner <dturner@twosigma.com> Helped-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2016-12-29auto gc: don't write bitmaps for incremental repacksLibravatar David Turner1-0/+25
When git gc --auto does an incremental repack of loose objects, we do not expect to be able to write a bitmap; it is very likely that objects in the new pack will have references to objects outside of the pack. So we shouldn't try to write a bitmap, because doing so will likely issue a warning. This warning was making its way into gc.log. When the gc.log was present, future auto gc runs would refuse to run. Patch by Jeff King. Bug report, test, and commit message by David Turner. Signed-off-by: David Turner <dturner@twosigma.com> Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2015-10-08pack-objects: do not get distracted by broken symrefsLibravatar Johannes Schindelin1-1/+1
It is quite possible for, say, a remote HEAD to become broken, e.g. when the default branch was renamed. We should still be able to pack our objects when such a thing happens; simply ignore broken symrefs (because they cannot matter for the packing process anyway). This fixes https://github.com/git-for-windows/git/issues/423 Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2015-10-05gc: demonstrate failure with stale remote HEADLibravatar Johannes Schindelin1-0/+13
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2013-10-18gc: remove gc.pid file at end of executionLibravatar Jonathan Nieder1-0/+5
This file isn't really harmful, but isn't useful either, and can create minor annoyance for the user: * It's confusing, as the presence of a *.pid file often implies that a process is currently running. A user running "ls .git/" and finding this file may incorrectly guess that a "git gc" is currently running. * Leaving this file means that a "git gc" in an already gc-ed repo is no-longer a no-op. A user running "git gc" in a set of repositories, and then synchronizing this set (e.g. rsync -av, unison, ...) will see all the gc.pid files as changed, which creates useless noise. This patch unlinks the file after the garbage collection is done, so that gc.pid is actually present only during execution. Future versions of Git may want to use the information left in the gc.pid file (e.g. for policies like "don't attempt to run a gc if one has already been ran less than X hours ago"). If so, this patch can safely be reverted. For now, let's not bother the users. Explained-by: Matthieu Moy <Matthieu.Moy@imag.fr> Signed-off-by: Jonathan Nieder <jrnieder@gmail.com> Improved-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2012-08-27Fix tests under GETTEXT_POISON on parseoptLibravatar Jiang Xin1-2/+2
Use the i18n-specific test functions in test scripts for parseopt tests. This issue was was introduced in v1.7.10.1-488-g54e6d: 54e6d i18n: parseopt: lookup help and argument translations when showing usage and been broken under GETTEXT_POISON=YesPlease since. Signed-off-by: Jiang Xin <worldhello.net@gmail.com> Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2010-10-22gc -h: show usage even with broken configurationLibravatar Nguyễn Thái Ngọc Duy1-0/+28
Given a request for command-line usage information rather than some more substantial action, the only friendly thing to do is to report the usage information as soon as possible and exit. Without this change, as "git gc" glances over the repository, it can be distracted by the desire to report a malformed configuration file. Noticed while working through reports from Duy's repository access checker. [jn: with rewritten log message and tests] Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com> Signed-off-by: Jonathan Nieder <jrnieder@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>