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| author |  Neeraj Singh <neerajsi@microsoft.com> | 2022-03-10 22:43:20 +0000 |
|---|---|---|
| committer |  Junio C Hamano <gitster@pobox.com> | 2022-03-10 15:10:22 -0800 |
| commit | abf38abec201cded6094801766d69e11a6c112b6 (patch) | |
| tree | f1258b40f52f600be015a365ae5e57ed3b977a33 /Documentation | |
| parent | wrapper: make inclusion of Windows csprng header tightly scoped (diff) | |
| download | tgif-abf38abec201cded6094801766d69e11a6c112b6.tar.xz | |
core.fsyncmethod: add writeout-only mode
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>
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/config/core.txt | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/Documentation/config/core.txt b/Documentation/config/core.txt index c04f62a54a..dbb134f713 100644 --- a/Documentation/config/core.txt +++ b/Documentation/config/core.txt @@ -547,6 +547,15 @@ core.whitespace:: is relevant for `indent-with-non-tab` and when Git fixes `tab-in-indent` errors. The default tab width is 8. Allowed values are 1 to 63. +core.fsyncMethod:: + A value indicating the strategy Git will use to harden repository data + using fsync and related primitives. ++ +* `fsync` uses the fsync() system call or platform equivalents. +* `writeout-only` issues pagecache writeback requests, but depending on the + filesystem and storage hardware, data added to the repository may not be + durable in the event of a system crash. This is the default mode on macOS. + core.fsyncObjectFiles:: This boolean will enable 'fsync()' when writing object files. + |