US Patent 9668020 Signature retrieval and matching for media monitoring

Methods, apparatus, systems and articles of manufacture to perform signature retrieval and matching for media monitoring are disclosed. Example methods disclosed herein can include querying a first table using a first site signature obtained from a monitored site, the first table including hash keys corresponding to respective reference signatures, the first table further including respective qualifier data descriptive of respective ones of the reference signatures, Such example methods can also include querying a second table using first qualifier data obtained from querying the first table using the first site signature, the first qualifier data descriptive of a first reference signature corresponding to a first hash key determined to match the first site signature. Such example methods can further include comparing a first block of site signatures with a portion of a plurality of blocks of reference signatures obtained from querying the second table using the first qualifier data.