On Friday 14 November 2003 03:05, Jan Wieck wrote:For sure the sync() needs to be replaced by the discussed fsync() of recently written files. And I think the algorithm how much and how often to flush can be significantly improved. But after all, this does not change the real checkpointing at all, and the general framework having a separate process is what we probably want.
Having fsync for regular data files and sync for WAL segment a comfortable compramise? Or this is going to use fsync for all of them.
IMO, with fsync, we tell kernel that you can write this buffer. It may or may not write it immediately, unless it is hard sync.
I think it's more the other way around. On some systems sync() might return before all buffers are flushed to disk, while fsync() does not.
Since postgresql can afford lazy writes for data files, I think this could work.
The whole point of a checkpoint is to know for certain that a specific change is in the datafile, so that it is safe to throw away older WAL segments.
Jan
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