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PostgreSQL 9.4 introduced Logical Decoding: http://www.postgresql.org/docs/9.4/static/logicaldecoding.html

It also has Cascade Streaming Replication: http://www.postgresql.org/docs/9.4/static/warm-standby.html#CASCADING-REPLICATION

Logical Decoding seems to be based on Streaming Replication. However a PostgreSQL server will refuse to start a Logical replication slot on a hot standby. It will only allow Logical Decoding on the master node.

What prevents a hot standby node to replicate itself in cascade using Logical Decoding?

Flyer
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2 Answers2

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A patch was submitted for PostgreSQL 10, but didn't get in.

Work continues for PostgreSQL 11.

Clients like pglogical will need modification to support streaming from a standby once the basic functionality is in postgres.

Craig Ringer
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A bit late...

It's essentially just unsupported because nobody had the time to implement it. There's a bunch of complications around reserving the required resources on the primary, and about continuing to correctly work when the standby, or one in a cascade above, is promoted. Nothing impossible, just work.

That kind of question you're probably more likely to get an answer about on the postgresql lists themselves.

Andres Freund
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  • Thank you for your answer. I was expecting that would be the case and it's good news in a sens. – Flyer Jun 11 '15 at 13:46