Sorry, this is second try to solve my problem.
I have problem in bad calculations inside trigger.
We use:
Server : Linux RedHat 7.2, IB 6.0.1, on 1.2GHz PIII, 512MB RAM, 2xHDD SCSI,
GDB size about 600MB, 15 connected users, many transactions every hour,

trigger after insert have to update cost of item table m9003 with data from
same table and table to which insert is pending,
so if it can't calculate properly all is wrong, tragedy etc.

trigger body (partial):

CREATE TRIGGER NG90035 FOR G90035
AFTER INSERT
POSITION 0
AS
DECLARE VARIABLE STANW DECIMAL(18,3);
DECLARE VARIABLE STANI DECIMAL(18,3);
DECLARE VARIABLE CENANOWA DECIMAL(18,3);
DECLARE VARIABLE CENASTARA DECIMAL(18,3);
BEGIN
IF (NEW.STRONA=1) THEN
BEGIN
SELECT SP_WI+ON_WI-ON_MI,(SP_WI+ON_WI-ON_MI)*CENA,CENA FROM M9003
WHERE
M9003.INDEKS=NEW.INDEKS INTO :STANI,:STANW,:CENASTARA;
IF (STANI+NEW.ILOSC>0.0) THEN

CENANOWA=(STANW+NEW.ILOSC*NEW.CENA)/(STANI+NEW.ILOSC); /*
here!!!*/
ELSE
CENANOWA=NEW.CENA;
UPDATE M9003 SET ON_WI=ON_WI+NEW.ILOSC,CENA=:CENANOWA WHERE
M9003.INDEKS=NEW.INDEKS;
END
..............
rest is not interesting

So:
in line /* here!!!*/
calculation of variable CENANOWA failed - after calculation
NEW.ILOSC*NEW.CENA is equal to 0, really it isn't true becouse if I post
this values into control table - everytime are not 0 both (they can't be 0).
Values are Null protected.
Trigger works good few days. In one day it fails (calculation new.ilosc *
new.cena ) and from this time fails often. Backup od GDB, computer restart
(server) helps, so it works good next few days (or few hours).

I do everything what I can imagine, change trigger text on many ways and
nothing can solve problem.

Any suggestions very welcome, here, or private szef@...

Wojtek