OSX 10.2.2 and beta 5

"Random" randomly fails. It is OK.

---------------------------------------------------------------------------

Theodore Petrosky wrote:

I just downloaded beta 5 and ran through a stock
config and make. make check comes up with 1 failure
listed as ignored..

parallel group (16 tests): select_distinct_on
transactions random select_having subselect
select_into select_distinct portals arrays union case
select_implicit hash_index aggregates join btree_index
select_into ... ok
select_distinct ... ok
select_distinct_on ... ok
select_implicit ... ok
select_having ... ok
subselect ... ok
union ... ok
case ... ok
join ... ok
aggregates ... ok
transactions ... ok
random ... failed (ignored)
portals ... ok
arrays ... ok
btree_index ... ok
hash_index ... ok
test privileges ... ok
test misc ... ok

=================================================
88 of 89 tests passed, 1 failed test(s) ignored.
==================================================

The differences that caused some tests to fail can be
viewed in the
file `./regression.diffs'. A copy of the test summary
that you see
above is saved in the file `./regression.out'.

Anyone interested in the `./regression.out' file?
The binary was created with ./configure and make on a
single processor G4 OSX 10.2.2. No options.

Ted

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Bruce Momjian <pgman@candle.pha.pa.us> writes:

"Random" randomly fails. It is OK.

So why is it a regression test, then?

Cheers,

Neil

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Neil Conway <neilc@samurai.com> writes:

Bruce Momjian <pgman@candle.pha.pa.us> writes:

"Random" randomly fails. It is OK.

So why is it a regression test, then?

It's hard to see how you could test random() in a completely
deterministic fashion ...

regards, tom lane

On Sat, Nov 16, 2002 at 15:18:58 -0500,
Tom Lane <tgl@sss.pgh.pa.us> wrote:

Neil Conway <neilc@samurai.com> writes:

Bruce Momjian <pgman@candle.pha.pa.us> writes:

"Random" randomly fails. It is OK.

So why is it a regression test, then?

It's hard to see how you could test random() in a completely
deterministic fashion ...

You could use the floor function and check that function call works and
that returned values are in the range >= 0 and < 1 (the description just
says between but this is the normal range).
You could also do a couple of selects that compare random's output to
each other to see if it is generating a constant. The odds of this
happening by chance are very small. If you tie a couple of these
together you should be able to reduce the chances to whatever you
think is safe.
The odds of the following returning true should be less than the chances
of a hardware hiccup:
select random() = random() and random() = random();
The following should always return 0 (assuming I am right about random
being strictly less than 1):
select floor(random());

You can probably come up with other tricks. For example for a large sample
you should be able to put a bound on the average for which the probability
of the average being outside that bound is comparable to the test for
random returning constant values.
The variance is something else that could be tested this way.