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4ebb7ad07d
Signed-off-by: Michael Schwarz <michi.schwarz@gmail.com> Reviewed-by: Jan Friesse <jfriesse@redhat.com>
117 lines
4.4 KiB
Plaintext
117 lines
4.4 KiB
Plaintext
SYNCHRONIZATION ALGORITHM:
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-------------------------
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The synchronization algorithm is used for every service in corosync to
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synchronize state of the system.
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There are 4 events of the synchronization algorithm. These events are in fact
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functions that are registered in the service handler data structure. They
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are called by the synchronization system whenever a network partitions or
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merges.
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init:
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Within the init event a service handler should record temporary state variables
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used by the process event.
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process:
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The process event is responsible for executing synchronization. This event
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will return a state as to whether it has completed or not. This allows for
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synchronization to be interrupted and recontinue when the message queue buffer
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is full. The process event will be called again by the synchronization service
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if requested to do so by the return variable returned in process.
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abort:
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The abort event occurs when during synchronization a processor failure occurs.
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activate:
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The activate event occurs when process has returned no more processing is
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necessary for any node in the cluster and all messages originated by process
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have completed.
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CHECKPOINT SYNCHRONIZATION ALGORITHM:
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------------------------------------
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The purpose of the checkpoint synchronization algorithm is to synchronize
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checkpoints after a partition or merge of two or more partitions. The
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secondary purpose of the algorithm is to determine the cluster-wide reference
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count for every checkpoint.
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Every cluster contains a group of checkpoints. Each checkpoint has a
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checkpoint name and checkpoint number. The number is used to uniquely reference
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an unlinked but still open checkpoint in the cluster.
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Every checkpoint contains a reference count which is used to determine when
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that checkpoint may be released. The algorithm rebuilds the reference count
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information each time a partition or merge occurs.
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local variables
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my_sync_state may have the values SYNC_CHECKPOINT, SYNC_REFCOUNT
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my_current_iteration_state contains any data used to iterate the checkpoints
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and sections.
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checkpoint data
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refcount_set contains reference count for every node consisting of
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number of opened connections to checkpoint and node identifier
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refcount contains a summation of every reference count in the refcount_set
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pseudocode executed by a processor when the synchronization service calls
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the init event
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call process_checkpoints_enter
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pseudocode executed by a processor when the synchronization service calls
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the process event in the SYNC_CHECKPOINT state
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if lowest processor identifier of old ring in new ring
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transmit checkpoints or sections starting from my_current_iteration_state
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if all checkpoints and sections could be queued
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call sync_refcounts_enter
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else
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record my_current_iteration_state
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require process to continue
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pseudocode executed by a processor when the synchronization service calls
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the process event in the SYNC_REFCOUNT state
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if lowest processor identifier of old ring in new ring
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transmit checkpoint reference counts
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if all checkpoint reference counts could be queued
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require process to not continue
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else
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record my_current_iteration_state for checkpoint reference counts
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sync_checkpoints_enter:
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my_sync_state = SYNC_CHECKPOINT
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my_current_iteration_state set to start of checkpoint list
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sync_refcounts_enter:
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my_sync_state = SYNC_REFCOUNT
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on event receipt of foreign ring id message
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ignore message
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pseudocode executed on event receipt of checkpoint update
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if checkpoint exists in temporary storage
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ignore message
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else
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create checkpoint
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reset checkpoint refcount array
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pseudocode executed on event receipt of checkpoint section update
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if checkpoint section exists in temporary storage
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ignore message
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else
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create checkpoint section
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pseudocode executed on event receipt of reference count update
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update temporary checkpoint data storage reference count set by adding
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any reference counts in the temporary message set to those from the
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event
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update that checkpoint's reference count
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set the global checkpoint id to the current checkpoint id + 1 if it
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would increase the global checkpoint id
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pseudocode called when the synchronization service calls the activate event:
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for all checkpoints
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free all previously committed checkpoints and sections
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convert temporary checkpoints and sections to regular sections
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copy my_saved_ring_id to my_old_ring_id
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pseudocode called when the synchronization service calls the abort event:
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free all temporary checkpoints and temporary sections
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