vault backup: 2025-03-17 10:54:23

Concurrent Systems/notes/5 - Software Transactional Memory.md

@@ -57,3 +57,19 @@ We now present an atomic STM system, called *Transactional Locking 2*:
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+
+### Virtual World Consistency
+Opacity requires a total order on all committed transactions and on all read prefixes of all aborted transactions
+	this latter requirement can be weakened by imposing that the read prefix of an aborted transaction is consistent only w.r.t its casual past (i.e. its virtual world).
+
+**Opacity:** total order both on all committed transactions and on read prefixes of aborted transactions
+
+**VWC:** total order on all committed transactions + partial order on committed transactions and the read prefixes of aborted transactions.
+
+The **casual past** of a transaction T is the set of all T' and T'' such that
+- T reads a value written by T'
+- T'' belongs to the casual past of T'
+
+VWC allows more transactions to commit -> it is a more liberal property than opacity.
+
+![[Pasted image 20250317105355.png]]