fdatasync — synchronize a file's in-core data with that on disk
#include <unistd.h>
int
fdatasync( |
int | fd) ; |
fdatasync
() flushes all data
buffers of a file to disk (before the system call returns).
It resembles fsync(2) but is not
required to update metadata such as the file last access
time.
Applications that access databases or log files often
write a tiny data fragment (e.g., one line in a log file) and
then call fsync(2) immediately in
order to ensure that the written data is physically stored on
the harddisk. Unfortunately, fsync(2) will always
initiate two write operations: one for the newly written data
and another one in order to update the modification time
stored in the inode. If the modification time is not a part
of the transaction concept fdatasync
() can be used to avoid
unnecessary inode disk write operations.
On success, zero is returned. On error, −1 is
returned, and errno
is set
appropriately.
fd
is not a
valid file descriptor open for writing.
An error occurred during synchronization.
fd
is bound
to a special file which does not support
synchronization.
On POSIX systems on which fdatasync
() is available, _POSIX_SYNCHRONIZED_IO
is defined in
<unistd.h>
to
a value greater than 0. (See also sysconf(3).)
In Linux 2.2 and earlier, fdatasync
() is equivalent to fsync(2), and so has no
performance advantage.
B.O. Gallmeister, POSIX.4, O'Reilly, pp. 220-223 and 343.
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