Robert Haas <robertmhaas@gmail.com> writes:
> On Fri, Mar 13, 2009 at 10:06 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> I assume you meant effective_io_concurrency. �We'd still need a special
>> case because the default is currently hard-wired at 1, not 0, if
>> configure thinks the function exists.
> I think 1 should mean no prefetching, rather than 0.
No, 1 means "prefetch a single block ahead". It doesn't involve I/O
concurrency in the sense of multiple I/O requests being processed at
once; what it does give you is CPU vs I/O concurrency. 0 shuts that
down and returns the system to pre-8.4 behavior.
regards, tom lane
