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diff --git a/README.recovery b/README.recovery new file mode 100644 index 0000000..bda564b --- /dev/null +++ b/README.recovery @@ -0,0 +1,116 @@ +SYNCHRONIZATION ALGORITHM: +------------------------- +The synchronization algorithm is used for every service in corosync to +synchronize state of the 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 requested 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 synchronization algorithm is to synchronize +checkpoints after a partition 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 cluster. + +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 synchronization 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 checkpoint 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 |