diff options
Diffstat (limited to 'note/replication.txt')
| -rw-r--r-- | note/replication.txt | 37 |
1 files changed, 30 insertions, 7 deletions
diff --git a/note/replication.txt b/note/replication.txt index c4bf46044..a151e80c3 100644 --- a/note/replication.txt +++ b/note/replication.txt @@ -59,11 +59,6 @@ If any "assign" request comes in 3. return a writable volume to the user -Plan: - Step 1. implement one copy(no replication), automatically assign volume ids - Step 2. add replication - -For the above operations, here are the todo list: for data node: 0. detect existing volumes DONE 1. onStartUp, and periodically, send existing volumes and maxVolumeCount store.Join(), DONE @@ -77,10 +72,38 @@ For the above operations, here are the todo list: 1. accept data node's report of existing volumes and maxVolumeCount ALREADY EXISTS /dir/join 2. periodically refresh for active data nodes, and adjust writable volumes 3. send command to grow a volume(id + replication level) DONE - 4. NOT_IMPLEMENTING: if dead/stale data nodes are found, for the affected volumes, send stale info - to other data nodes. BECAUSE the master will stop sending writes to these data nodes 5. accept lookup for volume locations ALREADY EXISTS /dir/lookup 6. read topology/datacenter/rack layout +An algorithm to allocate volumes evenly, but may be inefficient if free volumes are plenty: +input: replication=xyz +algorithm: +ret_dcs = [] +foreach dc that has y+z+1 volumes{ + ret_racks = [] + foreach rack with z+1 volumes{ + ret = select z+1 servers with 1 volume + if ret.size()==z+1 { + ret_racks.append(ret) + } + } + randomly pick one rack from ret_racks + ret += select y racks with 1 volume each + if ret.size()==y+z+1{ + ret_dcs.append(ret) + } +} +randomly pick one dc from ret_dcs +ret += select x data centers with 1 volume each + +A simple replica placement algorithm, but may fail when free volume slots are not plenty: +ret := []volumes +dc = randomly pick 1 data center with y+z+1 volumes + rack = randomly pick 1 rack with z+1 volumes + ret = ret.append(randomly pick z+1 volumes) + ret = ret.append(randomly pick y racks with 1 volume) +ret = ret.append(randomly pick x data centers with 1 volume) + + TODO: 1. replicate content to the other server if the replication type needs replicas |