Re: NFS performance tuning

Bruce Momjian wrote:
> Joseph Shraibman wrote:
>
>>Is it considered safe to run postgres over nfs if the sync option is used?
>
>
> No, because NFS is not atomic in its operations. However, a number of
> people are running PostgreSQL over NFS to network attached storage
> devices, and it seems to run fine --- I just am not sure what will
> happen if the network attached storage devices goes down.
>

From the FAQ at http://nfs.sourceforge.net/ :

Clients ensure that data that was written using a safe asynchronous write has been written
onto permanent storage using a new operation available in Version 3 called a COMMIT.
Servers do not send a response to a COMMIT operation until all data specified in the
request has been written to permanent storage. NFS Version 3 clients must protect buffered
data that has been written using a safe asynchronous write but not yet committed. If a
server reboots before a client has sent an appropriate COMMIT, the server can reply to the
eventual COMMIT request in a way that forces the client to resend the original write
operation. Version 3 clients use COMMIT operations when flushing safe asynchronous writes
to the server during a close(2) or fsync(2) system call, or when encountering memory pressure.