Re: index key limitation

On Wed, 20 Dec 2000, Dusty Spellman wrote: >There is a 390 byte limitation on the size of an index key value. Does >anybody know where this limitation comes from? Is it like the 16 column >limitation which is a limitation of the columns that can be tracked by the >sysindexes table? Traditionally, the limit was 120 bytes in SE and 255 bytes in OnLine. I don't know whether any product has a 390 byte limit. The 16 column limit arises from the design of the sysindexes table in IDS 7.x (it's a view in 9.x); the SE version of sysindexes only allows for 8 parts. The limitation on key size is largely arbitrary -- there is no inherent reason why there has to be any particular limit. However, if you are building a B-Tree, you don't want to have the key so long that you need to read multiple data pages to find the key, let alone the data record. So, there are pragmatic limits to how big the key should be, partly dictated by the page size. -- Yours, Jonathan Leffler (Jonathan.Leffler@Informix.com) #include <disclaimer.h> Guardian of DBD::Informix v1.00.PC1 -- http://www.perl.com/CPAN "I don't suffer from insanity; I enjoy every minute of it!"