1. A computer-implemented method comprising: storing, on a computer-readable storage medium, a first value that is based at least in part on a first quantity of occurrences of a first word in a plurality of documents and a second value that is based at least in part on a second quantity of occurrences of a second word in the plurality of documents; for at least part of a document of the plurality of documents: detecting that the first word and the second word both occur in the at least part of the document; generating a random number between a first number and a second number; using the first value and the second value to determine a third value that is based at least in part on both the first quantity of occurrences of the first word in the plurality of documents and the second quantity of occurrences of the second word in the plurality of documents, wherein the third value is less than the second number and greater than the first number; comparing the third value and the random number; and in response to the detecting and based at least in part on the comparing, determining whether to send an update to a count for the first word and the second word; wherein one or more updates, when sent, are sent using a communication interface; and wherein the method is performed by one or more computing devices.