Recovery algorithms described in this document.

git-svn-id: http://svn.fedorahosted.org/svn/corosync/trunk@1298 fd59a12c-fef9-0310-b244-a6a79926bd2f

README.recovery

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+SYNCHRONIZATION ALGORITHM:
+-------------------------
+The synchronization algorithm is used for every service in openais to
+synchronize state of he system.
+
+There are 4 events of the synchronization algorithm.  These events are in fact
+functions that are registered in the service handler data structure.  They
+are called by the synchronization system whenever a network partitions or
+merges.
+
+init:
+Within the init event a service handler should record temporary state variables
+used by the process event.
+
+process:
+The process event is responsible for executing synchronization.  This event
+will return a state as to whether it has completed or not.  This allows for
+synchronization to be interrupted and recontinue when the message queue buffer
+is full.  The process event will be called again by the synchronization service
+if requesed to do so by the return variable returned in process.
+
+abort:
+The abort event occurs when during synchronization a processor failure occurs.
+
+activate:
+The activate event occurs when process has returned no more processing is
+necessary for any node in the cluster and all messages originated by process
+have completed.
+
+CHECKPOINT SYNCHRONIZATION ALGORITHM:
+------------------------------------
+The purpose of the checkpoint syncrhonization algorithm is to synchronize
+checkpoints after a paritition or merge of two or more partitions.  The
+secondary purpose of the algorithm is to determine the cluster-wide reference
+count for every checkpoint.
+
+Every cluster contains a group of checkpoints.  Each checkpoint has a
+checkpoint name and checkpoint number.  The number is used to uniquely reference
+an unlinked but still open checkpoint in the cluser.
+
+Every checkpoint contains a reference count which is used to determine when
+that checkpoint may be released.  The algorithm rebuilds the reference count
+information each time a partition or merge occurs.
+
+local variables
+my_sync_state may have the values SYNC_CHECKPOINT, SYNC_REFCOUNT
+my_current_iteration_state contains any data used to iterate the checkpoints
+	and sections.
+checkpoint data
+	refcount_set contains reference count for every node consisting of
+	number of opened connections to checkpoint and node identifier
+	refcount contains a summation of every reference count in the refcount_set
+
+pseudocode executed by a processor when the syncrhonization service calls
+the init event
+	call process_checkpoints_enter
+
+pseudocode executed by a processor when the synchronization service calls
+the process event in the SYNC_CHECKPOINT state
+	if lowest processor identifier of old ring in new ring
+		transmit checkpoints or sections starting from my_current_iteration_state
+	if all checkpoints and sections could be queued
+		call sync_refcounts_enter
+	else
+		record my_current_iteration_state
+
+	require process to continue
+
+pseudocode executed by a processor when the synchronization service calls
+the process event in the SYNC_REFCOUNT state
+	if lowest processor identifier of old ring in new ring
+		transmit checkpoint reference counts
+	if all checkpoint reference counts could be queued
+		require process to not continue
+	else
+		record my_current_iteration_state for checkpoint reference counts
+
+sync_checkpoints_enter:
+	my_sync_state = SYNC_CHECKPOINT
+	my_current_iteration_state set to start of checkpont list
+
+sync_refcounts_enter:
+	my_sync_state = SYNC_REFCOUNT
+
+on event receipt of foreign ring id message
+	ignore message
+
+pseudocode executed on event receipt of checkpoint update
+	if checkpoint exists in temporary storage
+		ignore message
+	else
+		create checkpoint
+		reset checkpoint refcount array
+	
+pseudocode executed on event receipt of checkpoint section update
+	if checkpoint section exists in temporary storage
+		ignore message
+	else
+		create checkpoint section
+
+pseudocode executed on event receipt of reference count update
+	update temporary checkpoint data storage reference count set by adding
+	any reference counts in the temporary message set to those from the
+	event
+	update that checkpoint's reference count
+	set the global checkpoint id to the current checkpoint id + 1 if it
+	would increase the global checkpoint id
+
+pseudocode called when the synchronization service calls the activate event:
+for all checkpoints
+	free all previously committed checkpoints and sections
+	convert temporary checkpoints and sections to regular sections
+copy my_saved_ring_id to my_old_ring_id
+
+pseudocode called when the synchronization service calls the abort event:
+	free all temporary checkpoints and temporary sections