Added documentation and test for lock strategy

database/pgx/README.md

@@ -11,6 +11,8 @@ This package is for [pgx/v4](https://pkg.go.dev/github.com/jackc/pgx/v4). A back
 | `x-statement-timeout` | `StatementTimeout` | Abort any statement that takes more than the specified number of milliseconds |
 | `x-multi-statement` | `MultiStatementEnabled` | Enable multi-statement execution (default: false) |
 | `x-multi-statement-max-size` | `MultiStatementMaxSize` | Maximum size of single statement in bytes (default: 10MB) |
+| `x-lock-strategy` | `LockStrategy` | Strategy used for locking during migration (default: advisory) |
+| `x-lock-table` | `LockTable` | Name of the table which maintains the migration lock (default: schema_lock) |
 | `dbname` | `DatabaseName` | The name of the database to connect to |
 | `search_path` | | This variable specifies the order in which schemas are searched when an object is referenced by a simple name with no schema specified. |
 | `user` | | The user to sign in as |

database/pgx/pgx.go

@@ -218,6 +218,7 @@ func (p *Postgres) Open(url string) (database.Driver, error) {
 	}
 
 	lockStrategy := purl.Query().Get("x-lock-strategy")
+	lockTable := purl.Query().Get("x-lock-table")
 
 	px, err := WithInstance(db, &Config{
 		DatabaseName:          purl.Path,
@@ -227,6 +228,7 @@ func (p *Postgres) Open(url string) (database.Driver, error) {
 		MultiStatementEnabled: multiStatementEnabled,
 		MultiStatementMaxSize: multiStatementMaxSize,
 		LockStrategy:          lockStrategy,
+		LockTable:             lockTable,
 	})
 
 	if err != nil {
@@ -512,6 +514,12 @@ func (p *Postgres) Drop() (err error) {
 		if err := tables.Scan(&tableName); err != nil {
 			return err
 		}
+
+		// do not drop lock table
+		if tableName == p.config.LockTable && p.config.LockStrategy == LockStrategyTable {
+			continue
+		}
+
 		if len(tableName) > 0 {
 			tableNames = append(tableNames, tableName)
 		}

database/pgx/pgx_test.go

@@ -134,6 +134,32 @@ func TestMigrate(t *testing.T) {
 	})
 }
 
+func TestMigrateLockTable(t *testing.T) {
+	dktesting.ParallelTest(t, specs, func(t *testing.T, c dktest.ContainerInfo) {
+		ip, port, err := c.FirstPort()
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		addr := pgConnectionString(ip, port, "x-lock-strategy=table", "x-lock-table=lock_table")
+		p := &Postgres{}
+		d, err := p.Open(addr)
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer func() {
+			if err := d.Close(); err != nil {
+				t.Error(err)
+			}
+		}()
+		m, err := migrate.NewWithDatabaseInstance("file://./examples/migrations", "pgx", d)
+		if err != nil {
+			t.Fatal(err)
+		}
+		dt.TestMigrate(t, m)
+	})
+}
+
 func TestMultipleStatements(t *testing.T) {
 	dktesting.ParallelTest(t, specs, func(t *testing.T, c dktest.ContainerInfo) {
 		ip, port, err := c.FirstPort()