1. A computer program product comprising: a computer readable storage medium and program instructions stored on the computer readable storage medium, the program instructions comprising: program instructions to receive a capture log of a workload, wherein the workload includes a sequence of operations that are associated with a plurality of transactions, and wherein the plurality of transactions are instances of transaction types; program instructions to identify a first data structure that models, at least in part, the transaction types as sequences of nodes, wherein each node identifies a respective operation in the sequence of operations in the workload, and wherein the first data structure is stored in one or more primary memories such that an out-of-memory condition is not triggered; program instructions to read a task of an uncommitted transaction from the capture log, wherein a present operation and a transaction identifier are associated with the task; program instructions to dissociate the transaction identifier from a first node of the first data structure, wherein the first node identifies a prior operation of the uncommitted transaction; program instructions to associate the transaction identifier with a second node of the first data structure, wherein the second node identifies the present operation of the uncommitted transaction; program instructions to dissociate, in a second data structure, the first node from the transaction identifier, wherein the first node was associated with the transaction identifier in the second data structure based, at least in part, on the prior association between the first node and the transaction identifier in the first data structure, and wherein the second data structure is stored in the one or more primary memories such that the out-of-memory condition is not triggered; program instructions to associate, in the second data structure, the second node with the transaction identifier, wherein the present operation represents a most-recently-identified operation and, from among the sequences of nodes, each transaction identifier in the second data structure is associated with only a node representing a respective most-recently-identified operation based, at least in part, on associations between each transaction identifier and respective nodes in the sequences of nodes of the first data structure; and program instructions to generate, based, at least in part, on the first and the second data structures, a summary of the workload that includes signatures of the transaction types and a count of the instances of each of the transaction types.