set_compare#

Order the database’s keys by a sort sub of your own.

Synopsis#

$db->set_compare(sub { lc $a cmp lc $b });

Nothing. From then on every transaction uses the sub to place and find keys in this database.

The sub sees the two keys in $a and $b of its own package, as a sort block does, and returns less than, equal to or greater than zero.
The database does not remember the sub: set the same one every time the environment is opened, before the first read or write. Data stored under one order and read under another is not found.
A sub that dies makes the operation that called it croak with the sub’s error, after LMDB has finished it.
A plain value instead of a code reference croaks Peta::LMDB: set_compare needs a code reference.