An implementation repeatedly updates data in a data structure, the data structure having a size larger than an atomic size. The implementation avoids locking the data structure on every update, however. One method accesses data in a first portion of a data structure and estimates, based on the accessed data, an impact on data in a second portion of the data structure arising from an update to data in the first portion. The method then determines, based on the estimated impact, whether to lock the data structure during an update to data in the data structure. In a more particular example, a counter is copied on a regular basis. If only the least significant bits of the counter have changed, then an atomic instruction is used to copy only the least significant bits. However, when the more significant bits have changed, a lock is used to copy the entire counter.