I have Firebird database and I have created index on the varchar(30) field during active working name (I managed to complete and commit the create index statement, somtimes commit is not possible during working time, i.e., when there are other connections besides the active SYSDBA connection to the database) and after it I have started to receive error messages:
Implementation limit exceeded key size exceed implementation restriction for index INDEX_NAME
I can not reproduce such error message on my local databases for whom I have only one (SYSDBA) or only few non-SYSDBA connections. Is it possible that this limit exception is due to efforts to create index during active workload?
Of course, I am aware of http://edn.embarcadero.com/article/25723 and http://www.firebirdfaq.org/ip_ib_indexcalculator.htm but non-Unicode varchar(30) is definitely small enough to have its own index and table has only 3 other integer or date indices, so - the implementation limit could not have been reached.
Well, I am using Firebird 1.5 (it is deprecated already 10 years), but I guess that other versions can have such behavior as well.