Trigger for updating latest envelope runs per statement (#1596)

Instead of running the trigger per row like before, new trigger runs per
statement, which should be more performant on batch inserts.

Author: Maelkum

pkg/migrations/00018_add_latest_envelopes.down.sql

@@ -0,0 +1,9 @@
+-- First reinstate previous version of the trigger, as defined in 00006_add_latest_envelopes.up.sql
+CREATE TRIGGER gateway_latest_upd
+    AFTER INSERT ON gateway_envelopes_meta
+    FOR EACH ROW EXECUTE FUNCTION update_latest_envelope();
+
+
+DROP TRIGGER IF EXISTS gateway_latest_upd_v2 ON gateway_envelopes_meta;
+DROP FUNCTION IF EXISTS update_latest_envelope_v2();
+

pkg/migrations/00018_add_latest_envelopes.up.sql

@@ -0,0 +1,27 @@
+-- Run without timeout, needed as the insert can take a few seconds
+SET statement_timeout = 0;
+
+CREATE OR REPLACE FUNCTION update_latest_envelope_v2()
+RETURNS trigger AS $$
+BEGIN
+    INSERT INTO gateway_envelopes_latest as g
+    SELECT originator_node_id, MAX(originator_sequence_id) AS originator_sequence_id, MAX(gateway_time) AS gateway_time
+    FROM new
+    GROUP BY originator_node_id
+    ON CONFLICT (originator_node_id)
+    DO UPDATE
+        SET originator_sequence_id = EXCLUDED.originator_sequence_id,
+            gateway_time = EXCLUDED.gateway_time
+        WHERE EXCLUDED.originator_sequence_id > g.originator_sequence_id;
+    RETURN NULL;
+END;
+$$ LANGUAGE plpgsql;
+
+-- Create a new trigger that's per statement.
+CREATE TRIGGER gateway_latest_upd_v2
+    AFTER INSERT ON gateway_envelopes_meta
+    REFERENCING NEW TABLE AS new
+    FOR EACH STATEMENT EXECUTE FUNCTION update_latest_envelope_v2();
+
+-- Remove old trigger.
+DROP TRIGGER IF EXISTS gateway_latest_upd ON gateway_envelopes_meta;