1. A method, performed by a computer system having one or more processors and memory, the method comprising: detecting a request, received from a requestor, to access a first data object stored in a tiered data structure, the tiered data structure stored in one or more memory devices, wherein the tiered data structure includes a plurality of internal nodes and a plurality of leaf nodes; in response to detecting the request to access the first data object: retrieving a leaf node that includes the first data object; and locking the leaf node that includes the first data object; while the leaf node that includes the first data object is locked: transmitting, to the requestor, a first conditional-update communication that includes an indication of the current value of the first data object; and detecting a first conditional-update response corresponding to the first data object received from the requestor in response to the first conditional-update communication; and in response to detecting the first conditional-update response corresponding to the first data object, performing one or more operations based on the first conditional-update response corresponding to the first data object; and after performing the one or more operations based on the first conditional-update response corresponding to the first data object, unlocking the leaf node that includes the first data object.