wal: disable fsync() for avoiding write performance penalty
wal: disable fsync() for avoiding write performance penalty

It will keep application crash safe but it doesn't OS crash safe...

komainu8/groonga,groonga/groonga,komainu8/groonga,kenhys/groonga,komainu8/groonga,kenhys/groonga,kenhys/groonga,groonga/groonga,komainu8/groonga,komainu8/groonga,groonga/groonga,komainu8/groonga,kenhys/groonga,groonga/groonga,komainu8/groonga,komainu8/groonga,kenhys/groonga,groonga/groonga,kenhys/groonga,kenhys/groonga,groonga/groonga,groonga/groonga,kenhys/groonga,groonga/groonga