Re: Simplifying wal_sync_method

In summary, we added all those wal_sync_method values in hopes of
getting some data on which is best on which platform, but having gone
several years with few reports, I am thinking we should just choose the
best ones we can and move on, rather than expose a confusing API to the
users.

Does anyone show a platform where the *data* options are slower than the
non-*data* ones?

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pgman wrote:
> Tom Lane wrote:
> > Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> > > Currently, here are the options available for wal_sync_method:
> > > #wal_sync_method = fsync # the default varies across platforms:
> > > # fsync, fdatasync, fsync_writethrough,
> > > # open_sync, open_datasync
> >
> > > I don't understand why we support so many values.
> >
> > Because there are so many platforms with different subsets of these APIs
> > and different performance characteristics for the ones they do have.
>
> Right, and our current behavior makes it harder for people to even know
> the supported options.
>
> > > It seems 'fsync' should be fdatasync(), and if that is not available,
> > > fsync().
> >
> > I have yet to see anyone do any systematic testing of the different
> > options on different platforms. In the absence of hard data, proposing
> > that we don't need some of the options is highly premature.
>
> No one is every going to do it, so we might as well make the best guess
> we have. I think any platform where the *data* options are slower than
> the non-*data* options is broken, and if that logic holds, we might as
> well just use *data* by default if we can, which is my proposal.
>
> > > In fact, 8.1 uses O_DIRECT if available,
> >
> > That's a decision that hasn't got a shred of evidence to justify
> > imposing it on every platform.
>
> Right, and there is no evidence it hurts, so we do our best until
> someone comes up with data to suggest we are wrong. The same should be
> done with *data*.
>
> --
> Bruce Momjian | http://candle.pha.pa.us
> pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 359-1001
> + If your life is a hard drive, | 13 Roberts Road
> + Christ can be your backup. | Newtown Square, Pennsylvania 19073

--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073