dtSearch Text Retrieval Engine Programmer's Reference
dtsIndexCacheOptions::maxCount Data Member

Maximum number of indexes to keep in the cache

int maxCount;

The maximum number indexes to keep in the cache cannot be changed unless the cache does not contain any indexes that are in use (being used to for a search in progress). If any indexes are currently in use, an attempt to change maxCount will be ignored. 

The actual number of open indexes in a cache will depend on the level of activity. For example, if the cache has maxCount set to 10 but only one index is being searched on a single thread, the cache will never contain more than one index. On the other hand, if the a single index is being searched on three threads, the cache may have up to three instances of that index.