fdatasync() flushes all data buffers of a file to disk (before the system
call returns). It resembles
fsync() but is not required to update the metadata such as 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() immediately in order to ensure that the written data is physically
stored on the harddisk. Unfortunately,
fsync() 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.
