1. A method for performing an online migration of a plurality of databases between server systems, the method comprising: initiating transfer, from a source database server in a source server system to a target database server in a target server system, of a plurality of databases, wherein the source server system is online and responding to database requests during transfer of the plurality of databases, and wherein the source database server and the target database server are distinct servers; for each particular database within the plurality of databases: determining, using a scheduler computer system, a particular time at which the particular database is to be copied to the target database server; initializing, by the scheduler computer system, copying of the particular database to the target database server at the determined particular time; and recording, by the source server system, a chronological indication of when the copying of the particular database was initialized by the scheduler computer system, wherein the copying of each of the plurality of databases is initialized by the scheduler computer system at a different time, and wherein the copying of each of the plurality of databases requires a different length of time; during the copying of the plurality of databases, receiving, by the source server system, a plurality of change requests, each change request associated with at least one of the plurality of databases; storing, by the source server system, the plurality of change requests and, for each change request of the plurality of change requests, a chronological indication of when the change request was received; and for each particular change request of the received plurality of change requests: determining one or more of the particular databases affected by the particular change request; comparing the chronological indication of when the particular change request was received to the one or more chronological indications of when the copying of the one or more of the particular affected databases was initialized; and determining whether to apply the particular change request to the source server system or the target server system, based on the comparison of the chronological indication of when the particular change request was received to the chronological indications of when the copying of the particular affected databases was initialized; and verifying, by the target server system, the plurality of databases.