Re: [v9.2] make_greater_string() does not return a string in some cases

Robert Haas <robertmhaas@gmail.com> writes:
> On Thu, Sep 22, 2011 at 8:59 AM, Greg Stark <stark@mit.edu> wrote:
>> But the whole problem is that not all the strings with the initial
>> substring are in a contiguous block.

> If that were true for the sorts of indexes we're using for LIKE
> queries, the existing approach wouldn't work either.

Right.  Since it's not a problem for the sorts of indexes with which we
can use LIKE, moving knowledge of LIKE into the btree machinery doesn't
buy us a darn thing, except more complexity in a place where we can ill
afford it.  The essential problem here is "when can you stop scanning,
given a pattern with this prefix?", and btree doesn't know any more
about that than make_greater_string does; it would in fact have to use
make_greater_string or something isomorphic to it.
        regards, tom lane