When does a node checkpoint itself

Question

I understand there\'s some annotation related to @Suspendable to mark a function as serialisable. How much does a flow checkpoint itself?

Does a node c

Answer 1

@Suspendable marks a function as potentially suspendable. The flow is actually suspended only when one of the following operations is performed:

• Flow start
• send
• receive
• sendAndReceive
• waitForLedgerCommit
• getFlowInfo
• sleep

When one of these operations is performed, the node uses Quasar to capture the execution stack and create a checkpoint. If a function does not perform any of these operations, no checkpoints will be created. This is true even if the flow is doing heavy computation and/or the function is marked @Suspendable. In other words, Quasar does not do preemption, meaning we don't "checkpoint periodically", but only at specific call sites.

For example, here is the sequence of checkpoints in a simple flow:

@Suspendable fun call() { // checkpoint! sendSomething() computeSomething() } @Suspendable fun sendSomething() { send() // checkpoint! } @Suspendable fun computeSomething() { heavyComputation() // no checkpoint! }