Re: Background writer process

Shridhar Daithankar wrote:

> 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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