Re: Potential Large Performance Gain in WAL synching

"Curtis Faith" <curtis@galtair.com> writes:
> The REAL issue and the one that will greatly affect total system
> throughput is that of contention on the file locks. Since fsynch needs to
> obtain a write lock on the file descriptor, as does the write calls which
> originate from XLogWrite as the writes are written to the disk, other
> back-ends will block while another transaction is committing if the
> log cache fills to the point where their XLogInsert results in a 
> XLogWrite call to flush the log cache.

But that's exactly *why* we have a log cache: to ensure we can buffer a
reasonable amount of log data between XLogFlush calls.  If the above
scenario is really causing a problem, doesn't that just mean you need
to increase wal_buffers?
        regards, tom lane