Determining DB type prior to open for DB- set_bt_compare()

Question

Presently, I am building an application that opens a table (BDB database)
that might be DB_BTREE or DB_HASH (depending on how the original user created it).
The problem is that I do not know in advance of the DB->open() call which it will be. If I call DB->set_bt_compare() prior to opening the "BDB database" (which is the order it must be done), even when the open type is DB_UNKNOWN, it errors if it turns out to be a type DB_HASH due to the BTREE comparison routine.
Is there a less expensive way to determine DB_BTREE/DB_HASH without doing an open first and hoping for the normal case, and retrying if it errors?
Thanks, Warren.

Answer 1

No, that will not help.
The problem is that I have an UN-opened DB that I have to use for establishing
the set_bt_compare() routine on. Your documentation states that this must
be done prior to calling DB->open(). But I don't know how the user originally
created it, so I don't know in advance what its type is.
So the problem is that I don't know if the "database" is a BTREE type. If it is,
then DB->open() works marvelously. If it is of DB_HASH type, it fails on me,
because it doesn't like the bt compare routine I gave it.
It would appear that my only recourse would be to release that failed DB instance,
create another, and not set the compare routine on a subsequent DB->open()
attempt. But opens are rather expensive, and so I don't really want to do it that way.
If I could set the compare routine after the DB->open(), I could know what type
the database is first, and then only set the bt compare routine if it applies. The
documentation says that it will be ignored if you set that after the open.
In my opinion, it would be better if DB->open() ignored the established bt
compare routine, if it doesn't apply (especially when DB_UNKNOWN was
provided as the type).
Remember that a user is calling my routine to open a BDB "database" that was
created (in a file) in some prior session. So I am calling db_create(), then
setting the bt compare, and then calling DB-open(). But I supply a type of
DB_UNKNOWN in the open() call, cause I don't know yet what it is.
My only other recourse is to save the type in another table (I have some overhead
tables ("databases")), but I was hoping for a DB way to do this instead, as that
would complicate things further.
I hope that clarifies.
Thanks, Warren.