1. A method of processing a search query from a user, said method comprising: executing the search query to generate a query result, wherein the query result comprises URLs of web pages that are responsive to the search query; for at least one of the URLs, applying a set of hash functions to the URL, and using a result of said set of hash functions to assess whether the URL is included in an event history of the user; and when the URL is included in the event history of the user, providing, in a search results page for said search query, an annotation indicating to the user that the URL was previously accessed; wherein the method comprises comparing a result of said set of hash functions to a user-specific Bloom filter associated with said user; said method performed by execution of program instructions by a server system that comprises computer hardware.