This PR adds a configuration option that can be used to inform the
kernel that we intent to page in much of the TSM files.
This madvise value has been problematic in the past when its been set,
so this option defaults to off. It may be useful to some users with slow
disks.
Fsyncs to the WAL can cause higher IO with lots of small writes or
slower disks. This reworks the previous wal fsyncing to remove the
extra goroutine and remove the hard-coded 100ms delay. Writes to
the wal still maintain the invariant that they do not return to the
caller until the write is fsync'd.
This also adds a new config options wal-fsync-delay (default 0s)
which can be increased if a delay is desired. This is somewhat useful
for system with slower disks, but the current default works well as
is.
Stuart Carnie
Mark Rushakoff
Edd Robinson
Jonathan A. Sternberg
Jason Wilder
Cory LaNou
Ben Johnson