1. One or more computer readable storage media comprising computer readable instructions which, when executed, implement a system comprising: an indexer configured to perform indexing on indexable items stored at a source, wherein the indexer is configured to prioritize indexing operations based on one or more queries, the indexing operations comprising building indices for the indexable items to facilitate searching over the source, wherein the indexer is further configured to insert indexable items into a stack and use the stack in association with corresponding priorities.