Database Technologies

The people using PostgreSQL and the Streaming Replication feature seem to ask many of the same questions: 1. How best to monitor Streaming Replication? 2. What is the best way to do that? 3. Are there alternatives, when monitoring on Standby, to using the pg_stat_replication view on Master? 4. How should I calculate replication lag-time, in seconds, minutes, etc.? In light of these commonly asked questions, I thought a blog would help. The following are some methods I’ve found to be useful. Monitoring is critical for large infrastructure deployments where you have Streaming Replication for: 1. Disaster recovery 2. Streaming Replication is for High Availability 3. Load balancing, when using Streaming Replication with Hot Standby PostgreSQL has some building blocks for replication monitoring, and the following are some important functions and views which can be use for monitoring the replication: 1. pg_stat_replication view on master/primary server.    This view helps in

Some thoughts always come in mind about standby terminologies. Once, Someone has asked question about Physical Standby of Oracle10g. Is Oracle10g Physical Standby a Hot Standby Or WarmStandby? Till Oracle 10g, Physical Standby of Oracle is a standby which has two mode: 1. Managed Recovery Mode 2. Read Only Mode. It cannot be in both mode at same time. If the standby is in recovery mode then, it's a Warm Standby and when its read only mode then, then it's lagging from Primary and would be able to response SELECT queries. Either way, till Oracle 10g physical standby was not meeting the requirement of Hot Standby. It was playing the role of Warm Standby. However, from Oracle 11g, Physical Standby can be Recovery mode and read only mode, both at the same time, which now fulfill the definition of Hot Standby. With the complexity of managing the Standby, licensing thing comes in Picture. PG9.0 onwards, PostgreSQL now has Cold Standby, Warm Standby and Hot Standby, with zero cost.