Re: Final(?) proposal for wal_sync_method changes

On Tuesday 07 December 2010 17:24:14 Tom Lane wrote:
> After reviewing the two ongoing threads about fixing the wal_sync_method
> fiasco, I think there is general agreement on these two points:
> 
> 1. open_datasync shouldn't be the default choice
> 2. O_DIRECT shouldn't be forcibly bundled in with O_DSYNC/O_SYNC
> 
> What I suggest we do about the latter is to invent two new
> wal_sync_method values,
> 	open_datasync_direct
> 	open_sync_direct
> which are defined only on platforms that define O_DIRECT (and O_DSYNC
> or O_SYNC respectively).  That puts it in the hands of the DBA whether
> we try to use O_DIRECT or not.  We'll still keep the hard-wired
> optimization of disabling O_DIRECT when archiving or walreceiver are
> active.
> 
> Dropping open_datasync as the first-choice default is something we have
> to back-patch, but I'm less sure about it being a good idea to
> back-patch the rearrangement of O_DIRECT management.  Somebody who'd
> explicitly specified open_sync or open_datasync as wal_sync_method
> would find its behavior changing under him, which might be bad.
I vote for changing the order but not doing the O_DIRECT stuff on the 
backbranches.

As I am not seeing myself or clients of mine ever using any O_*SYNC variant I 
am not strongly opionated about what to do there. But I guess adding those two 
variants is not really much work.

Thanks,

Andres