Add instructions for upgrading from repmgr2 to repmgr3

sql/repmgr2_repmgr3.sql

@@ -0,0 +1,76 @@
+/*
+ * Update a repmgr 2.x installation to repmgr 3.0
+ * ----------------------------------------------
+ *
+ * 1. Stop any running repmgrd instances
+ * 2. On the master node, execute the SQL statements listed below,
+ *    taking care to identify the master node and any inactive
+ *    nodes
+ * 3. Restart repmgrd (being sure to use repmgr 3.0)
+ */
+
+/*
+ * Set the search path to the name of the schema used by
+ * your rempgr installation
+ * (this should be "repmgr_" + the cluster name defined in
+ * 'repmgr.conf')
+ */
+
+-- SET search_path TO 'name_of_repmgr_schema';
+
+BEGIN;
+
+ALTER TABLE repl_nodes RENAME TO repl_nodes2_0;
+
+CREATE TABLE repl_nodes (
+  id               INTEGER PRIMARY KEY,
+  type             TEXT    NOT NULL CHECK (type IN('master','standby','witness')),
+  upstream_node_id INTEGER NULL REFERENCES repl_nodes (id),
+  cluster          TEXT    NOT NULL,
+  name             TEXT    NOT NULL,
+  conninfo         TEXT    NOT NULL,
+  slot_name        TEXT    NULL,
+  priority         INTEGER NOT NULL,
+  active           BOOLEAN NOT NULL DEFAULT TRUE
+);
+
+INSERT INTO repl_nodes
+           (id, type, cluster, name, conninfo, priority)
+     SELECT id,
+            CASE
+               WHEN witness IS TRUE THEN 'witness'
+               ELSE 'standby'
+            END AS type,
+            cluster,
+            name,
+            conninfo,
+            priority
+       FROM repl_nodes2_0;
+
+/*
+ * You'll need to set the master explicitly; the following query
+ * should identify the master node ID but will only work if all
+ * standby servers are connected:
+ *
+ * SELECT id FROM repmgr_test.repl_nodes WHERE name NOT IN (SELECT application_name FROM pg_stat_replication)
+ *
+ * If in doubt, execute 'repmgr cluster show' will definitively identify
+ * the master.
+ */
+UPDATE repl_nodes SET type = 'master' WHERE id = $master_id;
+
+/* If any nodes are known to be inactive, update them here */
+
+-- UPDATE repl_nodes SET active = FALSE WHERE id IN (...);
+
+/* When you're sure of your changes, commit them */
+
+-- COMMIT;
+
+
+/*
+ * execute the following command when you are sure you no longer
+ * require the old table:
+ */
+
+-- DROP TABLE repl_nodes2_0;