Fast prefix search?

HI. I'm writing a script which extracts text which starts with some string. I tried to solve this by using Berkeley DB's B-tree and found that PHP provides Berkeley DB access through DBA[1] module. But , as the doc says collectly, "functionality is limited to a common subset of features" so I couldn't fully utilize BDB. (especially lack of key_range[2] is critical one) I know it could be done by using RDBMS like MySQL but using such is not so easy and fast compared to dbm solutions. Are there any recommendations to solve this kind of problem? Thank you in advance. [1] http://php.oregonstate.edu/manual/en/ref.dba.php [2] http://www.oracle.com/technology/documentation/berkeley-db/db/api_c/frame.html