Streaming replication solution in Postgres

Question

I'm reading the article below how to achieve streaming replication in Postgres DB.

https://www.percona.com/blog/2018/09/07/setting-up-streaming-replication-postgresql

Some things are not quite clear

1) Are both DB instances active OR the slave instance is just a clone of master (o it communicates with master, but not the backend?

2) If DB master node failed, what will happen until second node will get back online? Is this covered by default by just having wal sender and wal receiver processes or something else needs to be added?

3) Which DB_HOST:PORT should be configured in the backend app if for example I have two backend nodes (both of them are active)?

Laurenz Albe · Accepted Answer · 2019-02-04 07:24:05Z

2

If hot_standby = on in postgresql.conf, clients can connect to the standby, but only read data and not modify them. The standby is an identical physical cooy of the primary, just as if you had copied it file by file.
If the primary fails, the standby will remain up and running, but you still can only read data until somebody promotes the standby. You have to understand that PostgreSQL does not ship with cluster software that allows this to happen automatically. You have to usr some other software like Patroni for that.
That depends on the API your software is using. With libpq (the C API) or JDBC you can have a connection string that contains both servers and will select the primary automatically, but with other clients you may have to use external load balancing software.

answered Feb 4, 2019 at 7:24

Laurenz Albe

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