Nowadays, a vast amount of information is collected in real-time on a daily basis via users' handheld devices, web based applications, and customer service interactions (among many others). The sheer volume of this data and the unprecedented rate at which it becomes available for processing, potentially combined with other attributes that are commonly met in traditional data sets, calls for novel online record linkage' techniques that can handle streams of data to discover records that refer to the same real-world entity. This paper introduces UniBlock, an online record linkage approach, supported by a novel data structure, that can adapt to any blocking algorithm to separate the most frequently accessed blocks from the rest, and maintain these blocks in main memory. In UniBlock, this separation is performed in a randomized way, where the probability of eviction of a block is inversely proportional to its,frequency of access, empowering our approach with simplicity and effectiveness. Additionally, UniBlock provides accurate estimations of the proportion of matching record pairs in the underlying data sets in sublinear running time. Through experimental evaluation, we show that our approach outperforms the state-of-the-art methods in both accuracy and efficiency, being able to scale well to data streams.