RE: RE: [COMMITTERS] pgsql/src/backend/access/transam ( xact.c xlog.c)

> > You are going to kernel call/yield anyway to fsync, so why
> > not try and if someone does the fsync, we don't need to do it.
> > I am suggesting re-checking the need for fsync after the return
> > from sleep(0).
>
> It might make more sense to keep a private copy of the last time
> the file was modified per-backend by that particular backend and
> a timestamp of the last fsync shared globally so one can forgo the
> fsync if "it hasn't been dirtied by me since the last fsync"
>
> This would provide a rendevous point for the fsync call although
> cost more as one would need to periodically call gettimeofday to
> set the modified by me timestamp as well as the post-fsync shared
> timestamp.

Already made, but without timestamps. WAL maintains last byte of log
written/fsynced in shmem, so XLogFlush(_last_byte_to_be_flushed_)
will do nothing if data are already on disk.

Vadim