1. A computer-implemented method for reducing processing latency for search queries, comprising: under control of one or more computer systems configured with executable instructions, receiving a search query to be executed against an index including a plurality of segments partitioned into a set of partitions, each partition corresponding to a range of segments of the plurality of segments; prior to executing the search query, determining a likelihood that the search query is able to be executed against the index according to the set of partitions within a specified amount of time using a respective processing device for each partition; and when the query is determined to be unlikely to be processed according to the set of partitions within the specified amount of time using the respective processing device: splitting the range of segments for each partition into at least a first portion and a second portion; assigning at least one additional processing device to process the second portion of the range of segments for each partition in response to a determination that the query is unlikely to be processed within the specified amount of time; and executing the search query against the index using, for each partition, the respective processing device for the first portion and the at least one additional processing device for the second portion; receiving responses from at least a minimum number of processing devices assigned to process the partitions; and starting a delay timer once the responses have been received from the minimum number of processing devices, wherein if results have not been received from all processing devices after a period of delay as determined by the delay timer, each partition for which results have not been received is assigned to a different processing device.