Preconditions-Based Algorithm for Safe Start of Replication in Fault-Tolerant PostgreSQL Cluster

Traditionally, fault-tolerant DBMS clusters using PostgreSQL or derivatives are built on replication machinery, operated via write-ahead log shipping. Default checks are aimed only at preserving the integrity of received records. In certain conditions replication start can lead to standby cluster node having data different from other nodes, or being unable to finish startup procedures. Existing high availability systems are forced to cope with the problem through recreating such nodes from backups, which is usually costly in terms of recovery time.To address this issue, we propose an algorithm to prevent replication start when it is guaranteed to lead to data differences or node startup failure. For detection of such cases node collects information about write-ahead logs in the cluster and performs additional checks. If replication was blocked, automatic node synchronization for consequent replication start is available.We have tested the algorithm on various real-world cluster confi gurations with simulated failures, and the experimental results indicate that algorithm substantially reduces the chance of nodes being non-eligible to restart.