Re: Defaulting wal_sync_method to fdatasync on Linux for 9.1?

Marti Raudsepp wrote:
> I will grant you that the details were wrong, but I stand by the conclusion.
> I can state for a fact that PostgreSQL's default wal_sync_method
> varies depending on the <fcntl.h> header.
>

Yes; it's supposed to, and that logic works fine on some other
platforms.  The question is exactly what the new Linux O_DSYNC behavior
is doing, in regards to whether it flushes drive caches out or not.
Until you've quantified which of the cases do that--which is required
for reliable operation of PostgreSQL--and which don't, you don't have
any data that can be used to draw a conclusion from.  If some setups are
faster because they write less reliably, that doesn't automatically make
them the better choice.

--
Greg Smith   2ndQuadrant US    greg@2ndQuadrant.com   Baltimore, MD
PostgreSQL Training, Services and Support        www.2ndQuadrant.us
"PostgreSQL 9.0 High Performance": http://www.2ndQuadrant.com/books