Re: lcr - walsender integration

Hi,

The current logical walsender integration looks like the following:

=# INIT_LOGICAL_REPLICATION 'text';
WARNING:  Initiating logical rep
WARNING:  reached consistent point, stopping!
 replication_id | consistent_point | snapshot_name | plugin
----------------+------------------+---------------+--------
 id-2           | 3/CACBDF98       | 0xDEADBEEF    | text
(1 row)

=# START_LOGICAL_REPLICATION 'id-2' 3/CACBDF98;
...


So the current protocol is:
INIT_LOGICAL_REPLICATION '$plugin';
returns
* slot
* first consistent point
* snapshot id

START_LOGICAL_REPLICATION '$slot' $last_received_lsn;

streams changes, each wrapped in a 'w' message with (start, end) set to
the same value. The content of the data is completely free-format and
only depends on the output plugin.

Feedback is provided from the client via the normal 'r' messages.

I think thats not a bad start, but we probably can improve it a bit:

INIT_LOGICAL_REPLICATION '$slot' '$plugin' ($value = $key, ...);
START_LOGICAL_REPLICATION '$slot' $last_received_lsn;
STOP_LOGICAL_REPLICATION '$slot';

The option to INIT_LOGICAL_REPLICATION would then get passed to the
'pg_decode_init' output plugin function (i.e. a function of that name
would get dlsym()'ed using the pg infrastructure for that).

Does that look good to you? Any suggestions?

Greetings,

Andres

-- 
 Andres Freund	                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services