This variable allows you to flush the disk buffers after a certain number of
file updates has occurred. For example, if you set this variable to "10", then
the buffers are flushed after every ten updates to disk files. Only indexed
files are counted. When the buffers are flushed, the exact action depends on the
operating system:
MS-DOS (including the Windows environment) - MS-DOS's buffers are written to disk
and the file's directory information is updated. This is roughly equivalent to
the action that occurs when a file is closed.
OS/2 - This variable has no effect.
UNIX - The "sync" system routine is called. This causes all of UNIX's cache to be
written to disk. This operation is only scheduled - it occurs when the system
finds time to do it. Because the system does this every 30 seconds anyway,
probably the only reason to request a call to "sync" is if you have unreliable
power.
VMS - VMS does not have a system cache, so this variable has no effect.
Windows NT/Windows 2000 - Handled the same as under MS-DOS.