Detecting the read-write separation function

Information in thepgxc_node table before read-write separation is started:

postgres=# select oid, node_name, node_type from pgxc_node;
  oid  | node_name | node_type  
-------+-----------+-----------
 16384 | gcn1      | C
 11955 | cn1       | C
 16385 | cn2       | C
 16386 | cn3       | C
 16387 | cn4       | C
 16388 | dn1_1     | D
 16389 | dn2_1     | D
 16390 | dn3_1     | D
 16391 | dn4_1     | D
(9 rows)

There is no slave node information, so the read operation is sent to the master node.

postgres=# explain (analyze,verbose) select * from t_demo where id =10;
                                                       QUERY PLAN                                                        
------------------------------------------------------------------------------------------------------------------------
 Data Node Scan on "__REMOTE_FQS_QUERY__"  (cost=0.00..0.00 rows=0 width=0) (actual time=10.700..10.705 rows=1 loops=1)
   Output: t_demo.id, t_demo.name
   Node/s: dn2_1
   Remote query: SELECT id, name FROM public.t_demo t_demo WHERE (id = 10)
 Planning Time: 0.267 ms
 Execution Time: 10.745 ms
(6 rows)

dn2_1 is the master node.

After read-write separation is enabled, there is slave node information in thepgxc_node table of COD.

postgres=# select oid, node_name, node_type from pgxc_node;
  oid  | node_name | node_type  
-------+-----------+-----------
 16384 | gcn1      | C
 11955 | cn1       | C
 16385 | cn2       | C
 16386 | cn3       | C
 16387 | cn4       | C
 16388 | dn1_1     | D
 16389 | dn2_1     | D
 16390 | dn3_1     | D
 16391 | dn4_1     | D
 16402 | dn1_2     | E
 16403 | dn2_2     | E
 16404 | dn3_2     | E
 16405 | dn4_2     | E
(13 rows)

In the above result, the node of typeE is the slave node.

Read operations are sent to the slave node.

postgres=# explain (analyze,verbose) select * from t_demo where id =10;
                                                       QUERY PLAN                                                        
------------------------------------------------------------------------------------------------------------------------
 Data Node Scan on "__REMOTE_FQS_QUERY__"  (cost=0.00..0.00 rows=0 width=0) (actual time=17.571..17.576 rows=1 loops=1)
   Output: t_demo.id, t_demo.name
   Node/s: dn2_2
   Remote query: SELECT id, name FROM public.t_demo t_demo WHERE (id = 10)
 Planning Time: 0.319 ms
 Execution Time: 17.636 ms
(6 rows)

dn2_2 is the slave node.