MDEV-9058: protocol: COM_MULTI command (part 3)

Support of "previuousely used statement ID".
All IDs with highest bit ON reserved for special use.

mysql-test/r/mysqld--help.result

@@ -1340,7 +1340,7 @@ performance-schema-max-rwlock-instances -1
 performance-schema-max-socket-classes 10
 performance-schema-max-socket-instances -1
 performance-schema-max-stage-classes 150
-performance-schema-max-statement-classes 180
+performance-schema-max-statement-classes 181
 performance-schema-max-table-handles -1
 performance-schema-max-table-instances -1
 performance-schema-max-thread-classes 50

mysql-test/suite/sys_vars/r/sysvars_server_notembedded.result

@@ -2965,9 +2965,9 @@ READ_ONLY	YES
 COMMAND_LINE_ARGUMENT	REQUIRED
 VARIABLE_NAME	PERFORMANCE_SCHEMA_MAX_STATEMENT_CLASSES
 SESSION_VALUE	NULL
-GLOBAL_VALUE	180
+GLOBAL_VALUE	181
 GLOBAL_VALUE_ORIGIN	COMPILE-TIME
-DEFAULT_VALUE	180
+DEFAULT_VALUE	181
 VARIABLE_SCOPE	GLOBAL
 VARIABLE_TYPE	BIGINT UNSIGNED
 VARIABLE_COMMENT	Maximum number of statement instruments.

sql/sql_class.cc

@@ -1426,6 +1426,7 @@ void THD::init(void)
   bzero((char *) &org_status_var, sizeof(org_status_var));
   start_bytes_received= 0;
   last_commit_gtid.seq_no= 0;
+  last_stmt= NULL;
   status_in_global= 0;
 #ifdef WITH_WSREP
   wsrep_exec_mode= wsrep_applier ? REPL_RECV :  LOCAL_STATE;

sql/sql_class.h

@@ -1965,6 +1965,13 @@ public:
 
   /* all prepared statements and cursors of this connection */
   Statement_map stmt_map;
+
+  /* Last created prepared statement */
+  Statement *last_stmt;
+  inline void set_last_stmt(Statement *stmt)
+  { last_stmt= (is_error() ? NULL : stmt); }
+  inline void clear_last_stmt() { last_stmt= NULL; }
+
   /*
     A pointer to the stack frame of handle_one_connection(),
     which is called first in the thread for handling a client

sql/sql_prepare.cc

@@ -326,8 +326,14 @@ find_prepared_statement(THD *thd, ulong id)
     To strictly separate namespaces of SQL prepared statements and C API
     prepared statements find() will return 0 if there is a named prepared
     statement with such id.
+
+    LAST_STMT_ID is special value which mean last prepared statement ID
+    (it was made for COM_MULTI to allow prepare and execute a statement
+    in the same command but usage is not limited by COM_MULTI only).
   */
-  Statement *stmt= thd->stmt_map.find(id);
+  Statement *stmt= ((id == LAST_STMT_ID) ?
+                    thd->last_stmt :
+                    thd->stmt_map.find(id));
 
   if (stmt == 0 || stmt->type() != Query_arena::PREPARED_STATEMENT)
     return NULL;
@@ -2569,7 +2575,10 @@ void mysqld_stmt_prepare(THD *thd, const char *packet, uint packet_length)
   {
     /* Statement map deletes statement on erase */
     thd->stmt_map.erase(stmt);
+    thd->clear_last_stmt();
   }
+  else
+    thd->set_last_stmt(stmt);
 
   thd->protocol= save_protocol;
 
@@ -3155,6 +3164,9 @@ void mysqld_stmt_close(THD *thd, char *packet)
   stmt->deallocate();
   general_log_print(thd, thd->get_command(), NullS);
 
+  if (thd->last_stmt == stmt)
+    thd->clear_last_stmt();
+
   DBUG_VOID_RETURN;
 }
 
@@ -3417,7 +3429,8 @@ end:
 
 Prepared_statement::Prepared_statement(THD *thd_arg)
   :Statement(NULL, &main_mem_root,
-             STMT_INITIALIZED, ++thd_arg->statement_id_counter),
+             STMT_INITIALIZED,
+             ((++thd_arg->statement_id_counter) & STMT_ID_MASK)),
   thd(thd_arg),
   result(thd_arg),
   param_array(0),

sql/sql_prepare.h

@@ -18,6 +18,10 @@
 
 #include "sql_error.h"
 
+
+#define LAST_STMT_ID 0xFFFFFFFF
+#define STMT_ID_MASK 0x7FFFFFFF
+
 class THD;
 struct LEX;