Multi-version Concurrency Control (MVCC)
PolarDB uses parallel raft protocol to coordinate multiple data chunk servers. PolarRaft is a consensus protocol inherited from Raft but it allows out-of-order I/O completion tolerance capabilities of database.
PolarDB uses a novel disk outage consistency snapshot. It does not block user I/O operations during snapshot. When user triggers snapshot event, polarCtrl (the control plane of polar file system) will notify polarSwitch (the API that identifies page id, offset information from compute nodes and identify storage nodes in chunck servers) to take a snapshot. Chunk server will then take a snapshot before committing the request. After chunck servers receive snapshot tag of requests, they will take a snapshot before the request and copy block mapping meta information. Future requests will modify chunks in copy-on-write mechanism. After snapshot finishes, polarDB will stop adding snapshot tag to requests and will stop copy-on-write.
https://www.alibabacloud.com/campaign/polardb-discount-icde-2018
Alibaba
2017