Re: gettimeofday is at the end of its usefulness?

On Tuesday, May 13, 2014, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> A recent question from Tim Kane prompted me to measure the overhead
> costs of EXPLAIN ANALYZE, which I'd not checked in awhile. Things
> are far worse than I thought. On my current server (by no means
> lavish hardware: Xeon E5-2609 @2.40GHz) a simple seqscan can run
> at something like 110 nsec per row:
>
> regression=# create table foo as select x as f1 from
> generate_series(1,1000000) x;
> SELECT 1000000
> regression=# vacuum foo;
> VACUUM
> regression=# explain analyze select * from foo;
> QUERY PLAN
>
> ---------------------------------------------------------------------------------------------------------------
> Seq Scan on foo (cost=0.00..14425.00 rows=1000000 width=4) (actual
> time=0.053..111.720 rows=1000000 loops=1)
> Planning time: 0.222 ms
> Execution time: 166.682 ms
> (3 rows)
>
> (and, btw, this is a debug build --- without assert and memory
> context checks it'd be faster.)
>
> The problem with this number is that a simple test program shows that
> gettimeofday() requires about 40 nsec on this hardware. That means
> that two-thirds of the above timing measurement is overhead.
>

I'm all for finding something better if we can, but in the mean time this
is certainly not unexpected, and isn't it exactly what "explain
(analyze,timing off)" was invented for?

Cheers,

Jeff