Add constraint to prevent duplicate headers

- Disallow inserts of headers with the same number, hash, and node
  fingerprint, since it will enable duplicate log fetching for the
  same header

Author: Rob Mulholand

db/migrations/00023_create_headers_table.sql

@@ -8,7 +8,8 @@ CREATE TABLE public.headers
     block_timestamp      NUMERIC,
     check_count          INTEGER NOT NULL DEFAULT 0,
     eth_node_id          INTEGER NOT NULL REFERENCES eth_nodes (id) ON DELETE CASCADE,
-    eth_node_fingerprint VARCHAR(128)
+    eth_node_fingerprint VARCHAR(128),
+    UNIQUE (block_number, hash, eth_node_fingerprint)
 );
 
 -- Index is removed when table is

db/schema.sql

@@ -921,6 +921,14 @@ ALTER TABLE ONLY public.header_sync_transactions
     ADD CONSTRAINT header_sync_transactions_pkey PRIMARY KEY (id);
 
 
+--
+-- Name: headers headers_block_number_hash_eth_node_fingerprint_key; Type: CONSTRAINT; Schema: public; Owner: -
+--
+
+ALTER TABLE ONLY public.headers
+    ADD CONSTRAINT headers_block_number_hash_eth_node_fingerprint_key UNIQUE (block_number, hash, eth_node_fingerprint);
+
+
 --
 -- Name: headers headers_pkey; Type: CONSTRAINT; Schema: public; Owner: -
 --

pkg/datastore/postgres/repositories/header_repository.go

@@ -41,7 +41,7 @@ func (repository HeaderRepository) CreateOrUpdateHeader(header core.Header) (int
 	hash, err := repository.getHeaderHash(header)
 	if err != nil {
 		if headerDoesNotExist(err) {
-			return repository.insertHeader(header)
+			return repository.InternalInsertHeader(header)
 		}
 		log.Error("CreateOrUpdateHeader: error getting header hash: ", err)
 		return 0, err
@@ -128,13 +128,21 @@ func (repository HeaderRepository) getHeaderHash(header core.Header) (string, er
 	return hash, err
 }
 
-func (repository HeaderRepository) insertHeader(header core.Header) (int64, error) {
+// Function is public so we can test insert being called for the same header
+// Can happen when concurrent processes are inserting headers
+// Otherwise should not occur since only called in CreateOrUpdateHeader
+func (repository HeaderRepository) InternalInsertHeader(header core.Header) (int64, error) {
 	var headerId int64
-	err := repository.database.QueryRowx(
-		`INSERT INTO public.headers (block_number, hash, block_timestamp, raw, eth_node_id, eth_node_fingerprint) VALUES ($1, $2, $3::NUMERIC, $4, $5, $6) RETURNING id`,
-		header.BlockNumber, header.Hash, header.Timestamp, header.Raw, repository.database.NodeID, repository.database.Node.ID).Scan(&headerId)
+	row := repository.database.QueryRowx(
+		`INSERT INTO public.headers (block_number, hash, block_timestamp, raw, eth_node_id, eth_node_fingerprint)
+		VALUES ($1, $2, $3::NUMERIC, $4, $5, $6) ON CONFLICT DO NOTHING RETURNING id`,
+		header.BlockNumber, header.Hash, header.Timestamp, header.Raw, repository.database.NodeID, repository.database.Node.ID)
+	err := row.Scan(&headerId)
 	if err != nil {
-		log.Error("insertHeader: error inserting header: ", err)
+		if err == sql.ErrNoRows {
+			return 0, ErrValidHeaderExists
+		}
+		log.Error("InternalInsertHeader: error inserting header: ", err)
 	}
 	return headerId, err
 }
@@ -146,5 +154,5 @@ func (repository HeaderRepository) replaceHeader(header core.Header) (int64, err
 		log.Error("replaceHeader: error deleting headers: ", err)
 		return 0, err
 	}
-	return repository.insertHeader(header)
+	return repository.InternalInsertHeader(header)
 }

pkg/datastore/postgres/repositories/header_repository_test.go

@@ -98,6 +98,20 @@ var _ = Describe("Block header repository", func() {
 			Expect(len(dbHeaders)).To(Equal(1))
 		})
 
+		It("does not duplicate headers in concurrent insert", func() {
+			_, err = repo.InternalInsertHeader(header)
+			Expect(err).NotTo(HaveOccurred())
+
+			_, err = repo.InternalInsertHeader(header)
+			Expect(err).To(HaveOccurred())
+			Expect(err).To(MatchError(repositories.ErrValidHeaderExists))
+
+			var dbHeaders []core.Header
+			err = db.Select(&dbHeaders, `SELECT block_number, hash, raw FROM public.headers WHERE block_number = $1`, header.BlockNumber)
+			Expect(err).NotTo(HaveOccurred())
+			Expect(len(dbHeaders)).To(Equal(1))
+		})
+
 		It("replaces header if hash is different", func() {
 			_, err = repo.CreateOrUpdateHeader(header)
 			Expect(err).NotTo(HaveOccurred())