colexecerror: further optimize BenchmarkSQLCatchVectorizedRuntimeError

Rather than creating and closing connections for each test case, we can
just reuse the same connections in the benchmark, which speeds it up
significantly (from about 4 min to 1 min).

Release note: None

Author: yuzefovich

pkg/sql/colexecerror/error_test.go

@@ -184,22 +184,32 @@ func BenchmarkSQLCatchVectorizedRuntimeError(b *testing.B) {
 	// crdb_test-build behavior.
 	defer colexecerror.ProductionBehaviorForTests()()
 
-	for _, parallelism := range []int{1, 8, 32} {
+	const maxParallelism = 32
+	maxNumConns := runtime.GOMAXPROCS(0) * maxParallelism
+	// Create as many warm connections as we will need for the benchmark. These
+	// will be reused across all test cases to avoid the connection churn.
+	connsPool := make([]*gosql.DB, maxNumConns)
+	for i := range connsPool {
+		conn := s.ApplicationLayer().SQLConn(b, serverutils.DBName(""))
+		// Make sure we're using local, vectorized execution.
+		sqlDB := sqlutils.MakeSQLRunner(conn)
+		sqlDB.Exec(b, "SET distsql = off")
+		sqlDB.Exec(b, "SET vectorize = on")
+		connsPool[i] = conn
+	}
+
+	for _, parallelism := range []int{1, 8, maxParallelism} {
 		numConns := runtime.GOMAXPROCS(0) * parallelism
 		b.Run(fmt.Sprintf("conns=%d", numConns), func(b *testing.B) {
 			for _, tc := range cases {
 				stmt := fmt.Sprintf(sqlFmt, tc.builtin)
 				b.Run(tc.name, func(b *testing.B) {
-					// Create as many warm connections as we will need for the benchmark.
 					conns := make(chan *gosql.DB, numConns)
 					for i := 0; i < numConns; i++ {
-						conn := s.ApplicationLayer().SQLConn(b, serverutils.DBName(""))
-						// Make sure we're using local, vectorized execution.
-						sqlDB := sqlutils.MakeSQLRunner(conn)
-						sqlDB.Exec(b, "SET distsql = off")
-						sqlDB.Exec(b, "SET vectorize = on")
-						// Warm up the connection by executing the statement once. We should
-						// always go through the query plan cache after this.
+						conn := connsPool[i]
+						// Warm up the connection by executing the statement
+						// once. We should always go through the query plan
+						// cache after this.
 						_, _ = conn.Exec(stmt)
 						conns <- conn
 					}
@@ -209,7 +219,6 @@ func BenchmarkSQLCatchVectorizedRuntimeError(b *testing.B) {
 						var conn *gosql.DB
 						select {
 						case conn = <-conns:
-							defer conn.Close()
 						default:
 							b.Fatal("not enough warm connections")
 						}