MDEV-19237 Skip sending metadata when possible for binary protocol.

Do not resend metadata, if metadata does not change between prepare and
execute of prepared statement, or between executes.

Currently, metadata of *every* prepared statement will be checksummed,
and change is detected once checksum changes.

This is not from ideal, performance-wise. The code for
better/faster detection of unchanged metadata, is already in place, but
currently disabled due to PS bugs, such as MDEV-23913.

1 files changed, 119 insertions, 0 deletions

diff --git a/tests/mysql_client_test.c b/tests/mysql_client_test.c
index e043eeebdec..644bc129a5f 100644
--- a/tests/mysql_client_test.c
+++ b/tests/mysql_client_test.c
@@ -21147,6 +21147,124 @@ static void test_execute_direct()
 #endif
 }
 
+
+static void assert_metadata_skipped_count_equals(MYSQL *mysql, int val)
+{
+  MYSQL_ROW row;
+  MYSQL_RES *result;
+  int rc= mysql_query(mysql, "SELECT VARIABLE_VALUE FROM INFORMATION_SCHEMA.SESSION_STATUS WHERE "
+                         "VARIABLE_NAME='Resultset_metadata_skipped'");
+  myquery(rc);
+  result= mysql_use_result(mysql);
+  mytest(result);
+  row= mysql_fetch_row(result);
+  DIE_UNLESS(atoi(row[0]) == val);
+  mysql_free_result(result);
+}
+
+
+static void flush_session_status(MYSQL* mysql)
+{
+  int rc= mysql_query(mysql, "flush status");
+  myquery(rc);
+}
+
+
+static void exec_stmt(MYSQL_STMT* stmt)
+{
+  int rc= mysql_stmt_execute(stmt);
+  check_execute(stmt, rc);
+  rc= mysql_stmt_store_result(stmt);
+  check_execute(stmt, rc);
+}
+
+
+
+static void test_cache_metadata()
+{
+  char char_val[]= "blah";
+  int int_val = 1;
+  MYSQL_BIND param= {0};
+  my_bool is_null= FALSE;
+
+
+  MYSQL_STMT* stmt= mysql_stmt_init(mysql);
+  check_stmt(stmt);
+  int rc= mysql_stmt_prepare(stmt, "SELECT ?", -1);
+  myquery(rc);
+
+  param.buffer= char_val;
+  param.buffer_type= MYSQL_TYPE_STRING;
+  param.is_null= &is_null;
+  param.buffer_length = 4;
+
+  rc= mysql_stmt_bind_param(stmt,&param);
+  exec_stmt(stmt);
+
+  flush_session_status(mysql);
+  /* Execute the statement again, check that metadata is skipped*/
+  exec_stmt(stmt);
+  assert_metadata_skipped_count_equals(mysql, 1);
+
+  flush_session_status(mysql);
+  /*
+    Execute the statement again, such that metadata changes,
+    (using LONG parameter in bind for "SELECT ?", instead of string.
+    Check that metadata is NOT skipped.
+  */
+  param.buffer= &int_val;
+  param.buffer_type= MYSQL_TYPE_LONG;
+  param.is_null= &is_null;
+  rc= mysql_stmt_bind_param(stmt, &param);
+  exec_stmt(stmt);
+  assert_metadata_skipped_count_equals(mysql, 0);
+  mysql_stmt_close(stmt);
+
+
+  /*
+    Test with real table, and DDL which causes column info to be
+    changed.
+  */
+  stmt= mysql_stmt_init(mysql);
+
+  rc= mysql_query(
+      mysql, "CREATE OR REPLACE TABLE t1 (a int, b bigint) engine=memory");
+  myquery(rc);
+
+  flush_session_status(mysql);
+  check_stmt(stmt);
+  rc= mysql_stmt_prepare(stmt, "SELECT * from t1", -1);
+  myquery(rc);
+
+  exec_stmt(stmt);
+  /* Metadata skipped, since already sent with COM_STMT_PREPARE result.*/
+  assert_metadata_skipped_count_equals(mysql, 1);
+
+  flush_session_status(mysql);
+  exec_stmt(stmt);
+  /* Metadata skipped again*/
+  assert_metadata_skipped_count_equals(mysql, 1);
+
+  rc= mysql_query(mysql, "ALTER TABLE t1 MODIFY b CHAR(10)");
+  myquery(rc);
+
+  /* Column metadata WILL change for the next execution due to DDL*/
+  flush_session_status(mysql);
+  exec_stmt(stmt);
+  assert_metadata_skipped_count_equals(mysql, 0);
+
+  /* On reexecution, PS column metadata will NOT change. */
+  flush_session_status(mysql);
+  exec_stmt(stmt);
+  assert_metadata_skipped_count_equals(mysql, 1);
+
+  rc= mysql_query(mysql, "DROP TABLE t1");
+  myquery(rc);
+
+  mysql_stmt_close(stmt);
+}
+
+
 static struct my_tests_st my_tests[]= {
   { "disable_query_logs", disable_query_logs },
   { "test_view_sp_list_fields", test_view_sp_list_fields },
@@ -21446,6 +21564,7 @@ static struct my_tests_st my_tests[]= {
   { "test_mdev18408", test_mdev18408 },
   { "test_mdev20261", test_mdev20261 },
   { "test_execute_direct", test_execute_direct },
+  { "test_cache_metadata", test_cache_metadata},
   { 0, 0 }
 };