When searching over multiple databases, how do I convert an MSet entry to the sub-database and docid in it?


Document ids in the combined database are interleaved, so if docid_combined is the docid from the MSet, then the following C code implements this:

subdatabase_number = (docid_combined - 1) % number_of_databases; // First sub-database is 0.
docid_sub = (docid_combined - 1) / number_of_databases + 1;

Other languages

If you want to implement this in another language you should be able to adapt the C/C++ code above. Note that % means modulus in the above and / an integer division (truncating any fractional part towards zero).

Omega 1.4.7 and later

If you need to do this in an Omega template then 1.4.7 added $subdb{DOCID} and $subid{DOCID} to give you the name of the sub-database containing DOCID and the corresponding docid in that sub-database. You can use $subdb and $subid if you just want to use the current document in the hitlist.

Omega 1.4.6 and older

If you need to support older versions of Omega, this is equivalent to $subdb without an argument list:


And this to $subid without an argument list:


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