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

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.

Important

IMPLEMENTATION:

Fast recovery reference implementation.

Note

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