> You can use something like this to create index:
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I'm sorry to disagree, but - no, you can't. Per the docs:

    enable_cache
            When set to a true value, caching is used but only if you 
+gave
            *cache_file_name*. There is no default value here!

    cache_file_name
            The file used for caching. This option is mandatory if
            *enable_cache* is true.
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Neither of these is set in your code - and setting them does not create the specified file.

I've tried explicitly using '$mb->make_index' in my code, by the way - in which both of the above are defined (please see the code I originally posted.) The cache file still does not get created (and, yes, I do have write permissions in that directory; an 'open' call in the script creates one without any problem.) At this point, it's beginning to look like a module bug.