This commit introduces the infrastructure for the core.fsync
configuration knob. The repository components we want to sync
are identified by flags so that we can turn on or off syncing
for specific components.
If core.fsyncObjectFiles is set and the core.fsync configuration
also includes FSYNC_COMPONENT_LOOSE_OBJECT, we will fsync any
loose objects. This picks the strictest data integrity behavior
if core.fsync and core.fsyncObjectFiles are set to conflicting values.
This change introduces the currently unused fsync_component
helper, which will be used by a later patch that adds fsyncing to
the refs backend.
Actual configuration and documentation of the fsync components
list are in other patches in the series to separate review of
the underlying mechanism from the policy of how it's configured.
Helped-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Neeraj Singh <neerajsi@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit introduces the `core.fsyncMethod` configuration
knob, which can currently be set to `fsync` or `writeout-only`.
The new writeout-only mode attempts to tell the operating system to
flush its in-memory page cache to the storage hardware without issuing a
CACHE_FLUSH command to the storage controller.
Writeout-only fsync is significantly faster than a vanilla fsync on
common hardware, since data is written to a disk-side cache rather than
all the way to a durable medium. Later changes in this patch series will
take advantage of this primitive to implement batching of hardware
flushes.
When git_fsync is called with FSYNC_WRITEOUT_ONLY, it may fail and the
caller is expected to do an ordinary fsync as needed.
On Apple platforms, the fsync system call does not issue a CACHE_FLUSH
directive to the storage controller. This change updates fsync to do
fcntl(F_FULLFSYNC) to make fsync actually durable. We maintain parity
with existing behavior on Apple platforms by setting the default value
of the new core.fsyncMethod option.
Signed-off-by: Neeraj Singh <neerajsi@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The "GIT_TEST_FSYNC" environment variable now exists for
disabling fsync() even on packfiles and other "critical" data.
Running "make test -j8 NO_SVN_TESTS=1" on a noisy 8-core system
on an HDD, test runtime drops from ~4 minutes down to ~3 minutes.
Using "GIT_TEST_FSYNC=1" re-enables fsync() for comparison
purposes.
SVN interopability tests are minimally affected since SVN will
still use fsync in various places.
This will also be useful for 3rd-party tools which create
throwaway git repositories of temporary data, but remains
undocumented for end users.
Signed-off-by: Eric Wong <e@80x24.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This adds three new functions to pkt-line.c: packet_fwrite,
packet_fwrite_fmt and packet_fflush. Besides writing a pktline flush
packet, packet_fflush also flushes the stdio buffer of the stream.
Helped-by: Patrick Steinhardt <ps@pks.im>
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Jacob Vosmaer <jacob@gitlab.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Some platforms, like NonStop do not automatically restart fsync()
when interrupted by a signal, even when that signal is setup with
SA_RESTART.
This can lead to test breakage, e.g., where "--progress" is used,
thus SIGALRM is sent often, and can interrupt an fsync() syscall.
Make sure we deal with such a case by retrying the syscall
ourselves. Luckily, we call fsync() fron a single wrapper,
fsync_or_die(), so the fix is fairly isolated.
Reported-by: Randall S. Becker <randall.becker@nexbridge.ca>
Helped-by: Jeff King <peff@peff.net>
Helped-by: Taylor Blau <me@ttaylorr.com>
[jc: the above two did most of the work---I just tied the loose end]
Helped-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This is more consistent with the project style. The majority of Git's
source files use dashes in preference to underscores in their file names.
Signed-off-by: Stefan Beller <sbeller@google.com>
