The internal Database structure contains a map with the typedef CCByLoc and the name ccByLoc. This map is used to track client cursors that are using indexes, so that when an index is changed by deleting a btree bucket, all possible users of that bucket may be notified.

The ClientCursor::informAboutToDeleteBucket() routine will log a message saying "perf warning: byLoc.size=<size> in aboutToDeleteBucket" under some conditions. The "perf warning" is presumably because this may be expensive if there are a lot of entries in the map.

We could change the code so that fewer calls were needed by associating this map at a finer level of granularity, for example at the collection level.

We should probably remove this log message in any case, because there is nothing a user can really do about it and it isn't an error.