Commit 35491a4a authored by Julien Muchembled's avatar Julien Muchembled

Document cluster states

parent b1ea96c0
......@@ -78,12 +78,35 @@ def ErrorCodes():
def ClusterStates():
# Once the primary master is elected, the cluster has a state, which is
# initially RECOVERING, during which the master:
# - first recovers its own data by reading it from storage nodes;
# - waits for the partition table be operational;
# - automatically switch to VERIFYING if the cluster can be safely started.
# Whenever the partition table becomes non-operational again, the cluster
# goes back to this state.
# Transient state, used to:
# - replay the transaction log, in case of unclean shutdown;
# - and actually truncate the DB if the user asked to do so.
# Then, the cluster either goes to RUNNING or STARTING_BACKUP state.
# Normal operation. The DB is read-writable by clients.
# Transient state to shutdown the whole cluster.
# Transient state, during which the master (re)connect to the upstream
# master.
# Backup operation. The master is notified of new transactions thanks to
# invalidations and orders storage nodes to fetch them from upstream.
# Because cells are synchronized independently, the DB is often
# inconsistent.
# TODO: allow clients to connect for read-only operations
# Transient state, when the user decides to go back to RUNNING state.
# The master stays in this state until the DB is consistent again.
# In case of failure, the cluster will go back to backup mode.
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