projects / mirror_corosync.git / blame
| Commit | Line | Data |
|---|---|---|
| 3a34cba2 SD |
1 | SYNCHRONIZATION ALGORITHM: |
| 2 | ------------------------- | |
| dd3991c0 | 3 | The synchronization algorithm is used for every service in corosync to |
| 62148d10 | 4 | synchronize state of the system. |
| 3a34cba2 SD |
5 | |
| 6 | There are 4 events of the synchronization algorithm. These events are in fact | |
| 7 | functions that are registered in the service handler data structure. They | |
| 8 | are called by the synchronization system whenever a network partitions or | |
| 9 | merges. | |
| 10 | ||
| 11 | init: | |
| 12 | Within the init event a service handler should record temporary state variables | |
| 13 | used by the process event. | |
| 14 | ||
| 15 | process: | |
| 16 | The process event is responsible for executing synchronization. This event | |
| 17 | will return a state as to whether it has completed or not. This allows for | |
| 18 | synchronization to be interrupted and recontinue when the message queue buffer | |
| 19 | is full. The process event will be called again by the synchronization service | |
| 4ebb7ad0 | 20 | if requested to do so by the return variable returned in process. |
| 3a34cba2 SD |
21 | |
| 22 | abort: | |
| 23 | The abort event occurs when during synchronization a processor failure occurs. | |
| 24 | ||
| 25 | activate: | |
| 26 | The activate event occurs when process has returned no more processing is | |
| 27 | necessary for any node in the cluster and all messages originated by process | |
| 28 | have completed. | |
| 29 | ||
| 30 | CHECKPOINT SYNCHRONIZATION ALGORITHM: | |
| 31 | ------------------------------------ | |
| 4ebb7ad0 MS |
32 | The purpose of the checkpoint synchronization algorithm is to synchronize |
| 33 | checkpoints after a partition or merge of two or more partitions. The | |
| 3a34cba2 SD |
34 | secondary purpose of the algorithm is to determine the cluster-wide reference |
| 35 | count for every checkpoint. | |
| 36 | ||
| 37 | Every cluster contains a group of checkpoints. Each checkpoint has a | |
| 38 | checkpoint name and checkpoint number. The number is used to uniquely reference | |
| 4ebb7ad0 | 39 | an unlinked but still open checkpoint in the cluster. |
| 3a34cba2 SD |
40 | |
| 41 | Every checkpoint contains a reference count which is used to determine when | |
| 42 | that checkpoint may be released. The algorithm rebuilds the reference count | |
| 43 | information each time a partition or merge occurs. | |
| 44 | ||
| 45 | local variables | |
| 46 | my_sync_state may have the values SYNC_CHECKPOINT, SYNC_REFCOUNT | |
| 47 | my_current_iteration_state contains any data used to iterate the checkpoints | |
| 48 | and sections. | |
| 49 | checkpoint data | |
| 50 | refcount_set contains reference count for every node consisting of | |
| 51 | number of opened connections to checkpoint and node identifier | |
| 52 | refcount contains a summation of every reference count in the refcount_set | |
| 53 | ||
| 4ebb7ad0 | 54 | pseudocode executed by a processor when the synchronization service calls |
| 3a34cba2 SD |
55 | the init event |
| 56 | call process_checkpoints_enter | |
| 57 | ||
| 58 | pseudocode executed by a processor when the synchronization service calls | |
| 59 | the process event in the SYNC_CHECKPOINT state | |
| 60 | if lowest processor identifier of old ring in new ring | |
| 61 | transmit checkpoints or sections starting from my_current_iteration_state | |
| 62 | if all checkpoints and sections could be queued | |
| 63 | call sync_refcounts_enter | |
| 64 | else | |
| 65 | record my_current_iteration_state | |
| 66 | ||
| 67 | require process to continue | |
| 68 | ||
| 69 | pseudocode executed by a processor when the synchronization service calls | |
| 70 | the process event in the SYNC_REFCOUNT state | |
| 71 | if lowest processor identifier of old ring in new ring | |
| 72 | transmit checkpoint reference counts | |
| 73 | if all checkpoint reference counts could be queued | |
| 74 | require process to not continue | |
| 75 | else | |
| 76 | record my_current_iteration_state for checkpoint reference counts | |
| 77 | ||
| 78 | sync_checkpoints_enter: | |
| 79 | my_sync_state = SYNC_CHECKPOINT | |
| 4ebb7ad0 | 80 | my_current_iteration_state set to start of checkpoint list |
| 3a34cba2 SD |
81 | |
| 82 | sync_refcounts_enter: | |
| 83 | my_sync_state = SYNC_REFCOUNT | |
| 84 | ||
| 85 | on event receipt of foreign ring id message | |
| 86 | ignore message | |
| 87 | ||
| 88 | pseudocode executed on event receipt of checkpoint update | |
| 89 | if checkpoint exists in temporary storage | |
| 90 | ignore message | |
| 91 | else | |
| 92 | create checkpoint | |
| 93 | reset checkpoint refcount array | |
| 904a10ed | 94 | |
| 3a34cba2 SD |
95 | pseudocode executed on event receipt of checkpoint section update |
| 96 | if checkpoint section exists in temporary storage | |
| 97 | ignore message | |
| 98 | else | |
| 99 | create checkpoint section | |
| 100 | ||
| 101 | pseudocode executed on event receipt of reference count update | |
| 102 | update temporary checkpoint data storage reference count set by adding | |
| 103 | any reference counts in the temporary message set to those from the | |
| 104 | event | |
| 105 | update that checkpoint's reference count | |
| 106 | set the global checkpoint id to the current checkpoint id + 1 if it | |
| 107 | would increase the global checkpoint id | |
| 108 | ||
| 109 | pseudocode called when the synchronization service calls the activate event: | |
| 110 | for all checkpoints | |
| 111 | free all previously committed checkpoints and sections | |
| 112 | convert temporary checkpoints and sections to regular sections | |
| 113 | copy my_saved_ring_id to my_old_ring_id | |
| 114 | ||
| 115 | pseudocode called when the synchronization service calls the abort event: | |
| 116 | free all temporary checkpoints and temporary sections |