1. A computer implemented method comprising: receiving a query prefix from a user; obtaining a reference parameter for the user; identifying one or more likely queries that are likely to co-occur with the reference parameter in user activity sessions obtaining initial ranking scores for the one or more likely queries; computing, for each likely query of the one or more likely queries, a respective new ranking score including multiplying the initial ranking score for the likely query by a ranking factor associated with the likely query, wherein the ranking factor R is given by: R = P ⁡ ( x | q ) P ⁡ ( x ) , wherein P(x|q) is a measure of a likelihood of the likely query x occurring in a user activity session given that the reference parameter q also occurred in a same user activity session, and wherein P(x) is a measure of the likelihood of the likely query x appearing in a user activity session; determining a ranking of the one or more likely queries according to the new ranking scores; and providing the ranking of the one or more likely queries in response to receiving the query prefix.
1. A computer implemented method comprising: receiving a query prefix from a user; obtaining a reference parameter for the user; identifying one or more likely queries that are likely to co-occur with the reference parameter in user activity sessions obtaining initial ranking scores for the one or more likely queries; computing, for each likely query of the one or more likely queries, a respective new ranking score including multiplying the initial ranking score for the likely query by a ranking factor associated with the likely query, wherein the ranking factor R is given by: R = P ⁡ ( x | q ) P ⁡ ( x ) , wherein P(x|q) is a measure of a likelihood of the likely query x occurring in a user activity session given that the reference parameter q also occurred in a same user activity session, and wherein P(x) is a measure of the likelihood of the likely query x appearing in a user activity session; determining a ranking of the one or more likely queries according to the new ranking scores; and providing the ranking of the one or more likely queries in response to receiving the query prefix. 9. The method of claim 1 , wherein identifying one or more likely queries that are likely to co-occur with the reference parameter in user activity sessions comprises: determining that a process has registered a search of user activity sessions for the likely queries based on the reference parameter and the query prefix; and after the process has completed the search of user activity sessions for the likely queries based on the reference parameter and the query prefix, obtaining one or more likely queries from a result of the search.