Time-based transactional memories use time to reason about
the consistency of data accessed by transactions and about
the order in which transactions commit. They avoid the
large read overhead of transactional memories that always
check consistency when a new object is accessed, while still
guaranteeing consistency at all times—in contrast to trans-
actional memories that only check consistency on transac-
tion commit.
Current implementations of time-based transactional mem-
ories use a single global clock that is incremented by the
commit operation for each update transaction that commits.
In large systems with frequent commits, the contention on
this global counter can thus become a major bottleneck.
We present a scalable replacement for this global counter
and describe how the Lazy Snapshot Algorithm (LSA), which
forms the basis for our LSA-STM time-based software trans-
actional memory, has to be changed to support these new
time bases. In particular, we show how the global counter
can be replaced (1) by an external or physical clock that
can be accessed efficiently, and (2) by multiple synchronized
physical clocks.