A method for a playback device (200; 720) of a media playback system, the method comprising: receiving, via a network interface from a control device of a media playback system, one or more requests to play back media items that are indexed in a first index; in response to the requests, playing back the requested media items; tracking the received requests to play back the media items that are indexed in the first index; and characterised by: based on the tracked requests to play back media items that are indexed in the first index, determining, from among the media items that are indexed in the first index, a subset of media items that have been played back by the media playback system at least a pre-determined threshold number of times within a predetermined threshold period of time; indexing the determined subset of media items into a second index; receiving, via the network interface from a controller of the media playback system, a search request indicative of one or more particular media items; responsive to receiving the search request, determining whether the one or more particular media items are in the second index; when it is determined that the one or more particular media items are in the second index, transmitting an indication of the one or more particular media items to the controller of the media playback system; and when it is determined that the one or more particular media items are not in the second index, determining whether the one or more particular media items are in the first index. receiving, via a network interface from a control device of a media playback system, one or more requests to play back media items that are indexed in a first index; in response to the requests, playing back the requested media items; tracking the received requests to play back the media items that are indexed in the first index; and characterised by: based on the tracked requests to play back media items that are indexed in the first index, determining, from among the media items that are indexed in the first index, a subset of media items that have been played back by the media playback system at least a pre-determined threshold number of times within a predetermined threshold period of time; indexing the determined subset of media items into a second index; receiving, via the network interface from a controller of the media playback system, a search request indicative of one or more particular media items; responsive to receiving the search request, determining whether the one or more particular media items are in the second index; when it is determined that the one or more particular media items are in the second index, transmitting an indication of the one or more particular media items to the controller of the media playback system; and when it is determined that the one or more particular media items are not in the second index, determining whether the one or more particular media items are in the first index. based on the tracked requests to play back media items that are indexed in the first index, determining, from among the media items that are indexed in the first index, a subset of media items that have been played back by the media playback system at least a pre-determined threshold number of times within a predetermined threshold period of time; indexing the determined subset of media items into a second index; receiving, via the network interface from a controller of the media playback system, a search request indicative of one or more particular media items; responsive to receiving the search request, determining whether the one or more particular media items are in the second index; when it is determined that the one or more particular media items are in the second index, transmitting an indication of the one or more particular media items to the controller of the media playback system; and when it is determined that the one or more particular media items are not in the second index, determining whether the one or more particular media items are in the first index.