Distributed database MVCC reading and writing design

Distributed database data table is divided into multiple parition, distributed on different servers, topology is each server maintenance different version timestamp, compared to the single-machine database, provide MVCC is much more complex, of course, if you have spanner atomic clock, it would be much simpler.

A feasible implementation scheme is described.

This scenario can be guaranteed as follows:

• 1. Single partition read (Distributed transaction reading) take care of repeated read.

• 2 distributed transactions on the same server can guarantee repeated read, and the external guarantee causality sequence;

• 3. Cross-partition cannot guarantee causality, but can guarantee repeated read

Data model

• 1. Multiple parition on each server, each of which is a MVCC data structure that has multiple versions
• 2 Each server has a publish_id that indicates that data with a version less than this value can be read to
• 3 the previous trans_id for each server, indicating that the version of the subsequent write data is greater than this value

Distributed Transaction Write

• 1 in the prepare phase of the two-phase commit, the participant sends a prepare ACK with a version number, which is the value of the local ++trans_id
• 2 The coordinator selects the Max_ver with the largest timestamp in the collected Parepare ack, sending a commit
• 3 When the participant receives this request, writes the commit log and uses Max_ver to update the TRANS_ID
• 4 commit log after landing, modify publish_id, and release row lock

Distributed transaction Read

Because the distributed read of the cross-server does not make any guarantees, only the distributed read of the same server is discussed, in short, to publish_id as the version number, if there is a row lock on the target line, and the row lock related version number is less than publish_id, then block waits for row lock release, Otherwise, it can be read directly. Nweet/stackedit

Distributed database MVCC reading and writing design