Augment Code vs Copilot

augment-vs-copilot.md

We are facing some issues and want to understand what is happening analyzing log messages.

Context:

• https://github.com/untillpro/voedger/tree/732311621f1f682168b8b5ecee29ec855260de46

Prompt:

explain Key=1: compareAndSwap

Prompt for Copilot: which value is used to compare with?

Found it! Looking at impl.go:

ok, err := e.storage.CompareAndSwap(key, val, val, int(ttlSeconds))

Answer

The value being compared is val (the leadership value), and it's compared with itself (val → val).

Why compare with the same value?

This pattern is used for TTL renewal during leadership maintenance:

1. Old value: val - The current leader's identifier that was stored when leadership was first acquired
2. New value: val - The same identifier (no change)
3. Purpose:
   • Verify we still hold the leadership (the stored value matches our val)
   • Refresh the TTL to extend the leadership duration
   • Detect if someone else has taken over (if the value changed, CompareAndSwap returns false)

The flow

1. Acquire leadership: InsertIfNotExist(key, val, ttlSeconds) - Store initial value
2. Maintain leadership: Every ttlSeconds/2, call CompareAndSwap(key, val, val, ttlSeconds) to:
   • Confirm we're still the leader (value hasn't changed)
   • Reset the TTL clock
3. If CAS fails: Someone changed the value or it expired → release leadership

So the "comparison" is actually a leadership verification + TTL refresh operation in one atomic step.