What's the maximum key size or index size?
Since keys use indexes, the size of key is limited to maximum size of the index. For Firebird 1.x the maximum index key size is 252 bytes. For Firebird 2.x it's the quarter of the page size (1024 bytes for 4k page).
The computation is not too simple, but you can use this on-line calculator by Ivan Prenosil:
In case Ivan's site is down, there's a copy here at Firebird FAQ:
Do you find this FAQ incorrect or incomplete? Please e-mail
needs to be changed. To ensure quality, each change is checked by our editors (and often tested on live Firebird
databases), before it enters the main FAQ database. If you desire so, the
changes will be credited to your name. To learn more, visit our add content
If you are a commercial tool maker and your tool features a great way to handle
the issue written about in this FAQ, please check out our advertisement
All contents are copyright © 2007-2018 FirebirdFAQ.org unless otherwise stated in the text.