$$ \newcommand \Vote {\mathrm{Vote}} \newcommand \Bundle {\mathrm{Bundle}} \newcommand \Cert {\mathit{cert}} \newcommand \Late {\mathit{late}} \newcommand \Redo {\mathit{redo}} \newcommand \Down {\mathit{down}} $$

Fast Recovery

On observing a timeout event of \( T = k\lambda_f + u \) where \( k \) is a positive integer and \( u \in [0, \lambda_f] \) sampled uniformly at random, the player attempts to resynchronize. Then,

• The player broadcasts* \( \Vote(I, r, p, \Late, v) \) if \( v = \sigma(S, r, p) \) is committable in \( (r, p) \).

• The player broadcasts* \( \Vote(I, r, p, \Redo, \bar{v}) \) if there does not exist a \( s_0 > \Cert \) such that \( \Bundle(r, p-1, s_0, \bot) \) was observed and there exists an \( s_1 > \Cert \) such that \( \Bundle(r, p-1, s_1, \bar{v}) \) was observed.

• Otherwise, the player broadcasts* \( \Vote(I, r, p, \Down, \bot \).

Finally, the player broadcasts all \( \Vote(I, r, p, \Late, v) \in V\), all \( \Vote(I, r, p, \Redo, v) \in V\), and all \( \Vote(I, r, p, \Down, \bot) \in V \) that it has observed.

⚙️ IMPLEMENTATION

Fast recovery reference implementation.

For a detailed pseudocode overview of the fast recovery routine, along with protocol recovery run examples, refer to the Algorand ABFT non-normative section.