Re: turning fsync off for WAL

On Mon, 2 Jun 2008, Ram Ravichandran wrote:

> My current plan is to mount an Amazon S3 bucket as a drive using
> PersistentFS which is a POSIX-compliant file system.

Are you sure this will work correctly for database use at all? The known
issue listed at http://www.persistentfs.com/documentation/Release_Notes
sounded like a much bigger consistancy concern than the fsync trivia
you're bringing up:

"In the current Technology Preview release, any changes to an open file's
meta data are not saved to S3 until the file is closed. As a result, if
PersistentFS or the system crashes while writing a file, it is possible
for the file size in the file's directory entry to be greater than the
actual number of file blocks written to S3..."

This sounds like you'll face potential file corruption every time the
database goes down for some reason, on whatever database files happen to
be open at the time.

Given the current state of EC2, I don't know why you'd take this approach
instead of just creating an AMI to install the database into.

--
* Greg Smith gsmith(at)gregsmith(dot)com http://www.gregsmith.com Baltimore, MD