> So 'idx' is usually used with data that don't change? How does
Not necessarily. It is just recommended that data are not inserted in
sequential order. This is usually not the case, otherwise you might find
a way to avoid it, or write a separate Lisp function (e.g. splay) that
> indexing in the database work for example?
This is a different mechanism. The database uses B-Trees, which will
always be balanced.
> > for example, convert a numeric key to a symbol with 'format', and
> Is this generally prefered to using lup?
I'm not sure what is more efficient. At least it takes less space, as it
uses the (otherwise unused) value cells of those transient symbols.
There is the conversion overhead, though.