Re: 9.1 got really fast ;)

On Mon, Oct 17, 2011 at 9:44 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Alban Hertroys <haramrae@gmail.com> writes:
>> On 17 October 2011 17:25, Steve Crawford <scrawford@pinpointresearch.com> wrote:
>>> Even stand-alone statements take place within a transaction - just not an
>>> explicit one.
>
>> I doubt that more than 2.368 ms passed between the start of a
>> transaction and the stand-alone statement it's wrapping though. Not
>> impossible, but clock skew seems more likely to me.
>
> We take some pains to ensure that the same gettimeofday reading is used
> for both a transaction's start timestamp and the statement timestamp of
> its first statement.  So I'm not sure what's up with Scott's report.
> But in the OP's EXPLAIN case, that's the difference between successive
> readings taken within the EXPLAIN code, so it's hard to see how to
> explain it in any other way than "your system clock went backwards".
> Possibly the underlying cause is clock skew between different processors
> on a multiprocessor machine?

Could be.  That machine has 48 AMD 61xx series cores in it.