14. One or more non-transitory computer-readable media storing instructions which, when executed by one or more computing devices, cause performance of operations for incrementally updating a multi-user document index distributed over a plurality of index servers, the operations comprising: generating an index mutation comprising one or more tokens, wherein the index mutation is based on identified differences between a new version of a document and a previous version of the document; wherein an index of the document is stored at an index server of the plurality of index servers; appending an indication of the index mutation and an associated time-based value to a log; reading the time-based value associated with the indication of the index mutation from the log and comparing the associated time-based value to a time-based value associated with the index of the document stored at the index server; wherein the time-based value associated with the index of the document stored at the index server represents a last-update time of the index of the document stored at the index server; and based at least in part on comparing the time-based value associated with the indication of the index mutation that was read from the log and the time-based value associated with the index of the document stored at the index server, providing the one or more tokens from the appended index mutation indication to the index server that stores the index of the document stored at the index server, wherein the providing causes the index server to use the one or more tokens to update the index of the document stored at the index server.
14. One or more non-transitory computer-readable media storing instructions which, when executed by one or more computing devices, cause performance of operations for incrementally updating a multi-user document index distributed over a plurality of index servers, the operations comprising: generating an index mutation comprising one or more tokens, wherein the index mutation is based on identified differences between a new version of a document and a previous version of the document; wherein an index of the document is stored at an index server of the plurality of index servers; appending an indication of the index mutation and an associated time-based value to a log; reading the time-based value associated with the indication of the index mutation from the log and comparing the associated time-based value to a time-based value associated with the index of the document stored at the index server; wherein the time-based value associated with the index of the document stored at the index server represents a last-update time of the index of the document stored at the index server; and based at least in part on comparing the time-based value associated with the indication of the index mutation that was read from the log and the time-based value associated with the index of the document stored at the index server, providing the one or more tokens from the appended index mutation indication to the index server that stores the index of the document stored at the index server, wherein the providing causes the index server to use the one or more tokens to update the index of the document stored at the index server. 16. The one or more non-transitory computer-readable media storing instructions of claim 14 , wherein the log is an append-only log.