4. The method of claim 1 , wherein the selected partition of the user-term index comprises a plurality of database shards organized by time, and indexing the term of the post and the post identifier into the selected partition of the user-term index comprises: selecting a record in a most recent database shard of the plurality of database shards, the record comprising the user identifier, the term identifier, and a list of post identifiers; and adding the post identifier into the list of post identifiers of the selected record in the most recent database shard.
8. The method of claim 4 , further comprising: determining that all of the shards are filled to capacity; and creating a new shard, and setting the new shard as the most recent database shard.