division by zero

I think this caused by floating point signals being reported by the OS,
while integer operations don't have signals. I suppose we could catch
the divide by zero easily. Folks?

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

Eric B.Ridge wrote:

I admit, I suck at math, but I really thought postgres would ERROR on
this:

foo=# select 1/0;
?column?
----------
0
(1 row)

More surprising is that this does ERROR:
foo=# select 1/0.0;
ERROR: division by zero on numeric

Is this a bug, or do I need to go back to high school algebra? "Both"
is an acceptable answer. :)

eric

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  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

"Eric B.Ridge" <ebr@tcdi.com> writes:

I admit, I suck at math, but I really thought postgres would ERROR on
this:

foo=# select 1/0;

There's something wrong with your platform, I think. I get an error on
both HPUX and Red Hat Linux. What platform is this? and what PG
version?

z=# select 1/0;
ERROR: floating point exception! The last floating point operation either exceeded legal ranges or was a divide by zero
z=#

regards, tom lane

On Friday, March 7, 2003, at 02:50 PM, Tom Lane wrote:

"Eric B.Ridge" <ebr@tcdi.com> writes:

I admit, I suck at math, but I really thought postgres would ERROR on
this:

foo=# select 1/0;

There's something wrong with your platform, I think. I get an error on
both HPUX and Red Hat Linux. What platform is this? and what PG
version?

I'm sorry. I know better.

% uname -a
Darwin foo.local. 6.4 Darwin Kernel Version 6.4: Wed Jan 29 18:50:42
PST 2003; root:xnu/xnu-344.26.obj~1/RELEASE_PPC Power Macintosh powerpc
Which translates to Mac OS X 10.2.4 (6I32)

foo=# select version();
version
------------------------------------------------------------------------
--------------------------
PostgreSQL 7.3.2 on powerpc-apple-darwin6.4, compiled by GCC gcc (GCC)
3.1 20020420 (prerelease)

select 1/0; fails as expected on my x86 Linux box, so yer right, it's
just my little Mac. "I switched because Mac's can divide by zero."

eric

"Eric B. Ridge" <ebr@tcdi.com> writes:

select 1/0; fails as expected on my x86 Linux box, so yer right, it's
just my little Mac. "I switched because Mac's can divide by zero."

Mph. I have a Mac handy, will look into this.

Can anyone confirm whether the error shows up on other BSD-derived
platforms?

regards, tom lane

En un mensaje anterior, Tom Lane escribi�:

Can anyone confirm whether the error shows up on other BSD-derived
platforms?

FreeBSD 4.7-RELEASE-p7

db=# SELECT version();
version
---------------------------------------------------------------------
PostgreSQL 7.3.2 on i386-portbld-freebsd4.7, compiled by GCC 2.95.4
(1 row)

db=# SELECT 1/0;
ERROR: floating point exception! The last floating point operation either
exceeded legal ranges or was a divide by zero

Regards.

mcs=# select 1/0;
ERROR: floating point exception! The last floating point operation either
exceeded legal ranges or was a divide by zero
mcs=# select version();
version
---------------------------------------------------------------------
PostgreSQL 7.2.1 on i386-portbld-freebsd4.5, compiled by GCC 2.95.3
(1 row)

-----Original Message-----
From: Fernando Schapachnik [mailto:fernando@mecon.gov.ar]
Sent: Friday, March 07, 2003 3:09 PM
To: Tom Lane
Cc: Eric B. Ridge; pgsql-general@postgresql.org
Subject: Re: [GENERAL] division by zero

En un mensaje anterior, Tom Lane escribió:

Can anyone confirm whether the error shows up on other BSD-derived
platforms?

FreeBSD 4.7-RELEASE-p7

db=# SELECT version();
version
---------------------------------------------------------------------
PostgreSQL 7.3.2 on i386-portbld-freebsd4.7, compiled by GCC 2.95.4
(1 row)

db=# SELECT 1/0;
ERROR: floating point exception! The last floating point operation either
exceeded legal ranges or was a divide by zero

Regards.

---------------------------(end of broadcast)---------------------------
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Error on BSD/OS too. I should have checked that.

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

Pam Wampler wrote:

mcs=# select 1/0;
ERROR: floating point exception! The last floating point operation either
exceeded legal ranges or was a divide by zero
mcs=# select version();
version
---------------------------------------------------------------------
PostgreSQL 7.2.1 on i386-portbld-freebsd4.5, compiled by GCC 2.95.3
(1 row)

-----Original Message-----
From: Fernando Schapachnik [mailto:fernando@mecon.gov.ar]
Sent: Friday, March 07, 2003 3:09 PM
To: Tom Lane
Cc: Eric B. Ridge; pgsql-general@postgresql.org
Subject: Re: [GENERAL] division by zero

En un mensaje anterior, Tom Lane escribi?:

Can anyone confirm whether the error shows up on other BSD-derived
platforms?

FreeBSD 4.7-RELEASE-p7

db=# SELECT version();
version
---------------------------------------------------------------------
PostgreSQL 7.3.2 on i386-portbld-freebsd4.7, compiled by GCC 2.95.4
(1 row)

db=# SELECT 1/0;
ERROR: floating point exception! The last floating point operation either
exceeded legal ranges or was a divide by zero

Regards.

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  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

On Friday, March 7, 2003, at 03:05 PM, Tom Lane wrote:

"Eric B. Ridge" <ebr@tcdi.com> writes:

select 1/0; fails as expected on my x86 Linux box, so yer right, it's
just my little Mac. "I switched because Mac's can divide by zero."

Mph. I have a Mac handy, will look into this.

I doubt this helps, but I just tried on my Mac against 7.2.3 and it
still returns zero.

eric

fyi, my mac running mac os 10.2.4 and postgres 7.3.1 returns zero also.

On Friday, March 7, 2003, at 02:36 PM, Eric B.Ridge wrote:

"Eric B. Ridge" <ebr@tcdi.com> writes:

select 1/0; fails as expected on my x86 Linux box, so yer right, it's
just my little Mac. "I switched because Mac's can divide by zero."

I checked into this, and indeed OS X 10.2 is behaving funny: integer
divide by zero doesn't raise any signal, it just returns a bogus answer.
They're within their rights to do so according to the ANSI C spec
(wherein division by zero is stated to have undefined behavior).
But since other BSD-derived Unixen all seem to raise SIGFPE, I can't
help wondering if this shouldn't be considered a bug.

I think we have three possible responses:

1. Put explicit tests for zero into the integer division SQL function
routines.

2. Consider this Apple's problem and file a bug report.

3. Both.

I don't care for answer #1 alone, because it would only catch zero
divides in the specific places we put in tests; internal errors would
likely go uncaught. So I think a complaint to Apple is in order.
I'm not sure whether to also put in zero-divide guards. Comments?

regards, tom lane

Tom Lane wrote:

I checked into this, and indeed OS X 10.2 is behaving funny: integer
divide by zero doesn't raise any signal, it just returns a bogus

answer.

They're within their rights to do so according to the ANSI C spec
(wherein division by zero is stated to have undefined behavior).
But since other BSD-derived Unixen all seem to raise SIGFPE, I can't
help wondering if this shouldn't be considered a bug.

FWIW, this also is a problem with some of the windows ports. For
example, 'select 0/0' is unpredictable and can cause the server to gpf
and restart. This does not include the SRA port, because I don't have
it.

Merlin

On Sat, 8 Mar 2003, Tom Lane wrote:

"Eric B. Ridge" <ebr@tcdi.com> writes:

select 1/0; fails as expected on my x86 Linux box, so yer right, it's
just my little Mac. "I switched because Mac's can divide by zero."

I checked into this, and indeed OS X 10.2 is behaving funny: integer
divide by zero doesn't raise any signal, it just returns a bogus answer.
They're within their rights to do so according to the ANSI C spec
(wherein division by zero is stated to have undefined behavior).
But since other BSD-derived Unixen all seem to raise SIGFPE, I can't
help wondering if this shouldn't be considered a bug.

I think we have three possible responses:

1. Put explicit tests for zero into the integer division SQL function
routines.

2. Consider this Apple's problem and file a bug report.

3. Both.

I don't care for answer #1 alone, because it would only catch zero
divides in the specific places we put in tests; internal errors would
likely go uncaught. So I think a complaint to Apple is in order.
I'm not sure whether to also put in zero-divide guards. Comments?

We probably should put in guards since relying on sane behavior for
division by zero is probably unsafe from a portability standpoint. This
could hide some internal error on a system that has this problem (since we
could otherwise put it into a regression test) but those systems are
currently broken if the internal error occurs anyway.

Tom Lane wrote:
<snip>

2. Consider this Apple's problem and file a bug report.

Is there a good place to report errors to Apple for this kind of thing?

Was chatting to one of the guys in the MacOSX development team at Apple
a while ago and can pursue it through there if needed.

:-)

Regards and best wishes,

Justin Clift

3. Both.

I don't care for answer #1 alone, because it would only catch zero
divides in the specific places we put in tests; internal errors would
likely go uncaught. So I think a complaint to Apple is in order.
I'm not sure whether to also put in zero-divide guards. Comments?

regards, tom lane

--
"My grandfather once told me that there are two kinds of people: those
who work and those who take the credit. He told me to try to be in the
first group; there was less competition there."
- Indira Gandhi

On Saturday, March 8, 2003, at 11:54 PM, Justin Clift wrote:

Tom Lane wrote:
<snip>

2. Consider this Apple's problem and file a bug report.

Is there a good place to report errors to Apple for this kind of thing?

The best place I can find is:
http://developer.apple.com/bugreporter/index.html

Unfortunately, there doesn't seem to be a way to query existing
reports... If there is, I can't find it.

Also, I can't help but wonder why Apple/DarwinTeam handle integer
division by zero this way. There must be a reason, which makes me
think that "[considering] this Apple's problem" might not work out for
postgres in the end.

eric

Hi guys,

Was just looking around Google for similar reports of errors and came
across this:

MacOS X Server Developer Release Notes: Core OS Runtime
http://www.geminisolutions.com/WebObjects_4.5/Documentation/Developer/YellowBox/ReleaseNotes/Runtime.html

Looks like this is a known problem (as of 1998) and may not have been fixed.

Further hits come up when searching on the Apple Developer Connection
site too:

http://developer.apple.com/cgi-bin/search.pl?&amp;q=divide+by+zero&amp;num=10&amp;lang=lang_en|lang_zh-CN|lang_fr|lang_de|lang_ja&amp;ie=utf8&amp;oe=utf8
(that should be all one line)

And this one looks potentially interesting:

http://developer.apple.com/technotes/tn2002/tn2053.html
(search in this page for "FE_ENABLE_DIVBYZERO")

Have asked the member of the Apple MacOS X Server team what he
recommends the best way to proceed is.

Regards and best wishes,

Justin Clift

Eric B.Ridge wrote:

On Saturday, March 8, 2003, at 11:54 PM, Justin Clift wrote:

Tom Lane wrote:
<snip>

2. Consider this Apple's problem and file a bug report.

Is there a good place to report errors to Apple for this kind of thing?

The best place I can find is:
http://developer.apple.com/bugreporter/index.html

Unfortunately, there doesn't seem to be a way to query existing
reports... If there is, I can't find it.

Also, I can't help but wonder why Apple/DarwinTeam handle integer
division by zero this way. There must be a reason, which makes me think
that "[considering] this Apple's problem" might not work out for
postgres in the end.

eric

--
"My grandfather once told me that there are two kinds of people: those
who work and those who take the credit. He told me to try to be in the
first group; there was less competition there."
- Indira Gandhi

Merlin Moncure wrote:

Tom Lane wrote:

I checked into this, and indeed OS X 10.2 is behaving funny: integer
divide by zero doesn't raise any signal, it just returns a bogus

answer.

They're within their rights to do so according to the ANSI C spec
(wherein division by zero is stated to have undefined behavior).
But since other BSD-derived Unixen all seem to raise SIGFPE, I can't
help wondering if this shouldn't be considered a bug.

FWIW, this also is a problem with some of the windows ports. For
example, 'select 0/0' is unpredictable and can cause the server to gpf
and restart. This does not include the SRA port, because I don't have
it.

I just tested the SRA Win32 threaded port and both SELECT 1/0 and SELECT
0/0 crash the process. I have reported this to Tatsuo.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

Bruce Momjian wrote:
<snip>

FWIW, this also is a problem with some of the windows ports. For
example, 'select 0/0' is unpredictable and can cause the server to gpf
and restart. This does not include the SRA port, because I don't have
it.

I just tested the SRA Win32 threaded port and both SELECT 1/0 and SELECT
0/0 crash the process. I have reported this to Tatsuo.

Reported the issue to the Apple guys earlier on today, but haven't heard
anything back from them yet.

Guess we'll have to wait a few days to find out where things are at in
regards to MacOS X.

Regards and best wishes,

Justin Clift

--
"My grandfather once told me that there are two kinds of people: those
who work and those who take the credit. He told me to try to be in the
first group; there was less competition there."
- Indira Gandhi

Bruce Momjian wrote:

I just tested the SRA Win32 threaded port and both SELECT 1/0 and

SELECT

0/0 crash the process. I have reported this to Tatsuo.

The PeerDirect version (beta4) does the same thing. This is the version
based on the 7.2.1 source that I have been testing for a while. If
there is a newer version than that I don't have it yet. The source is
not available so I can't verify the cause.

Merlin

The big question is how to fix this on Win32. Is a test in the integer
division routines enough? Is there a signal to catch on Win32?

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

Merlin Moncure wrote:

Bruce Momjian wrote:

I just tested the SRA Win32 threaded port and both SELECT 1/0 and

SELECT

0/0 crash the process. I have reported this to Tatsuo.

The PeerDirect version (beta4) does the same thing. This is the version
based on the 7.2.1 source that I have been testing for a while. If
there is a newer version than that I don't have it yet. The source is
not available so I can't verify the cause.

Merlin

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  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073