Replication protocol question for logical replication.

[Chris Travers <chris.travers@xxxxxxxxx>]

While we are building a streaming logical backup solution for our data warehouse environment, we made a surprising discovery that select statements could be executed in a replication connection but I cannot find any clear documentation that says this is supported but I think it ought to be since that way you can, for example, copy a table to stdout.

Is this expected?

Chriss-MBP:postgres christravers$ PGSSLMODE=prefer psql "host=localhost port=5432 dbname=postgres replication=database" -c "IDENTIFY_SYSTEM" 

      systemid       | timeline |  xlogpos   |  dbname  

---------------------+----------+------------+----------

 6562045063708868894 |        1 | 0/CC9F4920 | postgres

(1 row)

Chriss-MBP:postgres christravers$ PGSSLMODE=prefer psql "host=localhost port=5432 dbname=postgres replication=database" -c "SELECT VERSION()" 

                                                    version                                                    

---------------------------------------------------------------------------------------------------------------

 PostgreSQL 10.4 on x86_64-apple-darwin17.5.0, compiled by Apple LLVM version 9.1.0 (clang-902.0.39.2), 64-bit

(1 row)

I am asking because if this is clearly intended to be supported we would like to work with upstream library vendors to make sure this functionality is included. My reading of the docs is that parameterized queries are not possible but simple queries are.  Is this correct?

--

Best Wishes,

Chris Travers

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