Why is the replication lag so bad in PostgreSQL?

Why is the replication lag so bad in PostgreSQL?

PostgreSQL is designed to handle heavy and stressful loads, but sometimes (due to a bad configuration) your server might still go south. Identifying the replication lag in PostgreSQL is not a complicated task to do, but there are a few different approaches to look into the problem.

How does single master replication work in PostgreSQL?

In Single-Master Replication (SMR), changes to table rows in a designated master database server are replicated to one or more replica servers. The replicated tables in the replica database are not permitted to accept any changes (except from the master). But even if they do, changes are not replicated back to the master server.

How to know if PostgreSQL process has high memory utilization?

If you know that the PostgreSQL process is having a high memory utilization, but the logs didn’t help, you have another tool that can be useful here, pg_top. This tool is similar to the top linux tool, but it’s specifically for PostgreSQL.

When does automatic failover occur in PostgreSQL?

2. What Is Automatic Failover in PostgreSQL? Once physical streaming replication has been set up and configured in PostgreSQL, failover can take place if the primary server for the database fails.

What is the replication process in PostgreSQL called?

The process of copying data from a PostgreSQL database server to another server is called PostgreSQL Replication. The source database server is usually called the Master server, whereas the database server receiving the copied data is called the Replica server.

How is logical replication different from physical replication?

We use the term logical in contrast to physical replication, which uses exact block addresses and byte-by-byte replication. PostgreSQL supports both mechanisms concurrently, see Chapter 26. Logical replication allows fine-grained control over both data replication and security.

When do you commit a transaction in PostgreSQL?

So in With PostgreSQL, the time for a commit is (at minimum) the round trip between the primary and the standby. Read-only transactions will not be affected by that. As it evolves, PostgreSQL is continuously improving and yet its replication is diverse.

When was warm standby introduced in PostgreSQL?

Warm standby for PostgreSQL was implemented in version 8.2 (back in 2006) and was based on the log shipping method. This means that the WAL records are directly moved from one database server to another to be applied, or simply an analogous approach to PITR, or very much like what you are doing with rsync.

How can I measure delay time in PG Stat replication?

How can I measure delay time You can get the delay in bytes from the master side quite easily using pg_xlog_location_diff to compare the master’s pg_current_xlog_insert_location with the replay_location for that backend’s pg_stat_replication entry. This only works when run on the master.

How to check the drift in PG Stat replication?

In the primary side, you have to use the view pg_stat_replication and compare differents fields to see the drift. The function pg_xlog_location_diff give the drift in size : You can use the lag in monitoring tools, as gauge, to monitor your replication. If a standby is missing, you have to check in the log’s standby why.

How does a Wal file work in PostgreSQL?

Its approach is by transferring WAL records (a WAL file is composed of WAL records) on the fly (merely a record based log shipping), between a master server and one or several standby servers. This protocol does not need to wait for the WAL file to be filled, unlike file-based log shipping.