merged from gramsrv upstream

deploy/migrations/20260901000010_dispatch_outbox_append_head_noop.up.sql

@@ -0,0 +1,118 @@
+-- Producers hold a shared per-lane fence until commit. A consumer that may
+-- remove the last head takes the exclusive form in a preceding statement;
+-- after that fence is acquired, its DELETE sees every earlier append or every
+-- later append observes the missing marker and installs a new one.
+CREATE FUNCTION dispatch_outbox_lane_advisory_key(target_user_id bigint)
+RETURNS bigint
+LANGUAGE sql
+IMMUTABLE
+STRICT
+PARALLEL SAFE
+AS $$
+    SELECT hashtextextended('telesrv:dispatch-outbox-lane:' || target_user_id::text, 0)
+$$;
+
+DROP TRIGGER dispatch_outbox_insert_user_head ON dispatch_outbox;
+
+CREATE FUNCTION dispatch_outbox_insert_user_heads()
+RETURNS trigger
+LANGUAGE plpgsql
+AS $$
+BEGIN
+    PERFORM pg_advisory_xact_lock_shared(
+        dispatch_outbox_lane_advisory_key(streams.target_user_id)
+    )
+    FROM (
+        SELECT DISTINCT target_user_id
+        FROM new_rows
+        ORDER BY target_user_id
+    ) AS streams;
+
+    -- The anti-join avoids touching a committed mutable head. ON CONFLICT is
+    -- retained only for concurrent producers racing to create an empty lane.
+    WITH candidates AS MATERIALIZED (
+        SELECT DISTINCT ON (target_user_id)
+            target_user_id, id AS head_id, pts AS head_pts,
+            status, next_attempt_at, updated_at
+        FROM new_rows
+        ORDER BY target_user_id, pts, id
+    )
+    INSERT INTO dispatch_outbox_user_heads (
+        target_user_id, head_id, head_pts, status, next_attempt_at, updated_at
+    )
+    SELECT
+        c.target_user_id, c.head_id, c.head_pts,
+        c.status, c.next_attempt_at, c.updated_at
+    FROM candidates c
+    WHERE NOT EXISTS (
+        SELECT 1
+        FROM dispatch_outbox_user_heads existing
+        WHERE existing.target_user_id = c.target_user_id
+    )
+    ON CONFLICT (target_user_id) DO NOTHING;
+    RETURN NULL;
+END;
+$$;
+
+CREATE OR REPLACE FUNCTION dispatch_outbox_maintain_user_head()
+RETURNS trigger
+LANGUAGE plpgsql
+AS $$
+DECLARE
+    removed_head bigint;
+BEGIN
+    IF TG_OP = 'UPDATE' THEN
+        UPDATE dispatch_outbox_user_heads
+        SET status = NEW.status,
+            next_attempt_at = NEW.next_attempt_at,
+            updated_at = NEW.updated_at
+        WHERE target_user_id = NEW.target_user_id
+          AND head_id = NEW.id;
+        RETURN NULL;
+    END IF;
+
+    DELETE FROM dispatch_outbox_user_heads
+    WHERE target_user_id = OLD.target_user_id
+      AND head_id = OLD.id
+    RETURNING head_id INTO removed_head;
+
+    IF removed_head IS NOT NULL THEN
+        INSERT INTO dispatch_outbox_user_heads (
+            target_user_id, head_id, head_pts, status, next_attempt_at, updated_at
+        )
+        SELECT target_user_id, id, pts, status, next_attempt_at, updated_at
+        FROM dispatch_outbox
+        WHERE target_user_id = OLD.target_user_id
+        ORDER BY pts ASC, id ASC
+        LIMIT 1
+        ON CONFLICT (target_user_id) DO UPDATE
+        SET head_id = EXCLUDED.head_id,
+            head_pts = EXCLUDED.head_pts,
+            status = EXCLUDED.status,
+            next_attempt_at = EXCLUDED.next_attempt_at,
+            updated_at = EXCLUDED.updated_at
+        WHERE (EXCLUDED.head_pts, EXCLUDED.head_id) <
+              (dispatch_outbox_user_heads.head_pts, dispatch_outbox_user_heads.head_id);
+    END IF;
+    RETURN NULL;
+END;
+$$;
+
+CREATE TRIGGER dispatch_outbox_insert_user_head
+AFTER INSERT ON dispatch_outbox
+REFERENCING NEW TABLE AS new_rows
+FOR EACH STATEMENT
+EXECUTE FUNCTION dispatch_outbox_insert_user_heads();
+
+-- Repair any marker that may be absent when upgrading from an interrupted or
+-- older deployment. Startup migration runs before the dispatcher starts.
+INSERT INTO dispatch_outbox_user_heads (
+    target_user_id, head_id, head_pts, status, next_attempt_at, updated_at
+)
+SELECT DISTINCT ON (d.target_user_id)
+    d.target_user_id, d.id, d.pts, d.status, d.next_attempt_at, d.updated_at
+FROM dispatch_outbox d
+LEFT JOIN dispatch_outbox_user_heads h USING (target_user_id)
+WHERE h.target_user_id IS NULL
+ORDER BY d.target_user_id, d.pts, d.id
+ON CONFLICT (target_user_id) DO NOTHING;