By default, conditional look-ups in the Jet Data Manager will create table indexes to improve the performance of the look-up. On large data sets (eg., several million records), it is possible that the size, or the maintenance, of the index(es) being created outweigh the utility of having an index. In such a case, you can disable the automatic creation of indexes.
Locate the table that you wish to disable the creation of automatic indexes on.
In the Jet Data Manager, notice the fields being used on the join...
...Compare these to the index shown in SQL for the source table, and note how an index exists for the fields that comprise the join.
Edit the conditional look-up by right-clicking the field, and selecting Edit Conditional Lookup
Click the box to enable Manual index creation
Deploy and execute both the table containing the conditional look-up, and the source table that the conditional look-up was pulling the field from.
Notice that the index we saw in Step #1 is now gone