There's a time window after we call RotateFile() where autofile#index+1
does not exist. It will be created during the next call to Write(). BUT
if somebody calls NewReader() before Write(), it will fail with "open
/tmp/wal#index+1/wal: no such file or directory"
We must create file (either by calling gr.Head.openFile() or directly)
during NewReader() to ensure read calls succeed.
Closes#2538
* fix Group.RotateFile need call Flush() before rename. #2428
* fix some review issue. #2428
refactor Group's config: replace setting member with initial option
* fix a handwriting mistake
* fix a time window error between rename and write.
* fix a syntax mistake.
* change option name Get_ to With_
* fix review issue
* fix review issue
1) no need to stop the ticker in createTestGroup() method
2) now there is a symmetry - we start the ticker in OnStart(), we stop it
in OnStop()
Refs #2072
short: flushing the bufio buffer is not enough to ensure data
consistency.
long:
Saving an entry to the WAL calls writeLine to append data to the
autofile group backing the WAL, then calls group.Flush() to flush that
data to persistent storage. group.Flush() in turn proxies to
headBuf.flush(), flushing the active bufio.BufferedWriter. However,
BufferedWriter wraps a Writer, not another BufferedWriter, and the way
it flushes is by calling io.Writer.Write() to clear the BufferedWriter's
buffer. The io.Writer we're wrapping here is AutoFile, whose Write
method calls os.File.Write(), performing an unbuffered write to the
operating system, where, I assume, it sits in the OS buffers awaiting
sync. This means that Wal.Save does not, in fact, ensure the saved
operation is synced to disk before returning.