MDEV-11479 Improved wsrep_dirty_reads

     Tasks:-
         Changes in wsrep_dirty_reads variable
         1.) Global + Session scope (Current: session-only)
         2.) Can be set using command line.
         3.) Allow all commands that do not change data (besides SELECT)
         4.) Allow prepared Statements that do not change data
         5.) Works with wsrep_sync_wait enabled

mysql-test/suite/galera/r/galera_var_dirty_reads.result

@@ -3,6 +3,10 @@ INSERT INTO t1 VALUES(1);
 SELECT * FROM t1;
 i
 1
+create user user1;
+grant all privileges on *.* to user1;
+create user user2;
+grant all privileges on *.* to user2;
 SET @@global.wsrep_cluster_address = '';
 SET @@session.wsrep_dirty_reads=OFF;
 SET SESSION wsrep_sync_wait=0;
@@ -18,8 +22,74 @@ SET @@session.wsrep_dirty_reads=ON;
 SELECT * FROM t1;
 i
 1
+connect  con1, localhost, user1,,test,$NODE_MYPORT_2,$NODE_MYSOCK_2;
+SET SESSION wsrep_sync_wait=0;
+set session wsrep_dirty_reads=1;
+prepare stmt_show from 'select 1';
+prepare stmt_select from 'select * from t1';
+prepare stmt_insert from 'insert into t1 values(1)';
+set session wsrep_dirty_reads=0;
+execute stmt_show;
+ERROR 08S01: WSREP has not yet prepared node for application use
+execute stmt_select;
+ERROR 08S01: WSREP has not yet prepared node for application use
+execute stmt_insert;
+ERROR 08S01: WSREP has not yet prepared node for application use
+SET wsrep_dirty_reads=ON;
+select @@session.wsrep_dirty_reads;
+@@session.wsrep_dirty_reads
+1
+execute stmt_show;
+1
+1
+execute stmt_select;
+i
+1
+execute stmt_insert;
+ERROR 08S01: WSREP has not yet prepared node for application use
+SET @@global.wsrep_dirty_reads=ON;
+connect  con2, localhost, user2,,test,$NODE_MYPORT_2,$NODE_MYSOCK_2;
+select @@session.wsrep_dirty_reads;
+@@session.wsrep_dirty_reads
+1
+prepare stmt_show from 'select 1';
+prepare stmt_select from 'select * from t1';
+prepare stmt_insert from 'insert into t1 values(1)';
+execute stmt_show;
+1
+1
+execute stmt_select;
+i
+1
+execute stmt_insert;
+ERROR 08S01: WSREP has not yet prepared node for application use
+SET SESSION wsrep_sync_wait=1;
+execute stmt_show;
+1
+1
+execute stmt_select;
+i
+1
+execute stmt_insert;
+ERROR 08S01: WSREP has not yet prepared node for application use
+SET SESSION wsrep_sync_wait=7;
+execute stmt_show;
+1
+1
+execute stmt_select;
+i
+1
+execute stmt_insert;
+ERROR 08S01: WSREP has not yet prepared node for application use
+connection node_2;
+SET @@global.wsrep_dirty_reads=OFF;
+connection node_1;
 SELECT * FROM t1;
 i
 1
 DROP TABLE t1;
+drop user user1;
+drop user user2;
+disconnect node_2;
+disconnect node_1;
 # End of test

mysql-test/suite/galera/t/galera_var_dirty_reads.test

@@ -17,6 +17,11 @@ CREATE TABLE t1(i INT) ENGINE=INNODB;
 INSERT INTO t1 VALUES(1);
 SELECT * FROM t1;
 
+create user user1;
+grant all privileges on *.* to user1;
+create user user2;
+grant all privileges on *.* to user2;
+
 SET @@global.wsrep_cluster_address = '';
 SET @@session.wsrep_dirty_reads=OFF;
 
@@ -36,6 +41,67 @@ SET @@session.wsrep_dirty_reads=ON;
 
 SELECT * FROM t1;
 
+--enable_connect_log
+--connect (con1, localhost, user1,,test,$NODE_MYPORT_2,$NODE_MYSOCK_2)
+#Just test the session behavior
+SET SESSION wsrep_sync_wait=0;
+
+set session wsrep_dirty_reads=1;
+#Prepared statement creation should be allowed MDEV-11479
+prepare stmt_show from 'select 1';
+prepare stmt_select from 'select * from t1';
+prepare stmt_insert from 'insert into t1 values(1)';
+set session wsrep_dirty_reads=0;
+
+#No Preapare stmt/proceure will be allowed
+--error ER_UNKNOWN_COM_ERROR
+execute stmt_show;
+--error ER_UNKNOWN_COM_ERROR
+execute stmt_select;
+--error ER_UNKNOWN_COM_ERROR
+execute stmt_insert;
+
+SET wsrep_dirty_reads=ON;
+select @@session.wsrep_dirty_reads;
+#Only prepare statement which does not change data should be allowed
+execute stmt_show;
+execute stmt_select;
+--error ER_UNKNOWN_COM_ERROR
+execute stmt_insert;
+SET @@global.wsrep_dirty_reads=ON;
+
+--connect (con2, localhost, user2,,test,$NODE_MYPORT_2,$NODE_MYSOCK_2)
+#Just test the session behavior
+select @@session.wsrep_dirty_reads;
+
+prepare stmt_show from 'select 1';
+prepare stmt_select from 'select * from t1';
+prepare stmt_insert from 'insert into t1 values(1)';
+
+#Only prepare statement which does not change data should be allowed
+execute stmt_show;
+execute stmt_select;
+--error ER_UNKNOWN_COM_ERROR
+execute stmt_insert;
+
+#wsrep_dirty_read should work when wsrep_sync_wait is 1 or non zero
+#because we already are disconnected , So It does not make any sense
+#to wait for other nodes
+SET SESSION wsrep_sync_wait=1;
+execute stmt_show;
+execute stmt_select;
+--error ER_UNKNOWN_COM_ERROR
+execute stmt_insert;
+
+SET SESSION wsrep_sync_wait=7;
+execute stmt_show;
+execute stmt_select;
+--error ER_UNKNOWN_COM_ERROR
+execute stmt_insert;
+
+--connection node_2
+SET @@global.wsrep_dirty_reads=OFF;
+
 --disable_query_log
 --eval SET @@global.wsrep_cluster_address = '$wsrep_cluster_address_saved'
 --enable_query_log
@@ -45,6 +111,8 @@ SELECT * FROM t1;
 SELECT * FROM t1;
 # Cleanup
 DROP TABLE t1;
+drop user user1;
+drop user user2;
 
 # Restore original auto_increment_offset values.
 --source include/auto_increment_offset_restore.inc

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

@@ -5,12 +5,13 @@
 SET @wsrep_dirty_reads_session_saved = @@session.wsrep_dirty_reads;
 # default
 SELECT @@global.wsrep_dirty_reads;
-ERROR HY000: Variable 'wsrep_dirty_reads' is a SESSION variable
+@@global.wsrep_dirty_reads
+0
 SELECT @@session.wsrep_dirty_reads;
 @@session.wsrep_dirty_reads
 0
 
-# scope and valid values
+# valid values for session
 SET @@session.wsrep_dirty_reads=OFF;
 SELECT @@session.wsrep_dirty_reads;
 @@session.wsrep_dirty_reads
@@ -24,11 +25,29 @@ SELECT @@session.wsrep_dirty_reads;
 @@session.wsrep_dirty_reads
 0
 
+# valid values for global
+SET @@global.wsrep_dirty_reads=OFF;
+SELECT @@global.wsrep_dirty_reads;
+@@global.wsrep_dirty_reads
+0
+SET @@global.wsrep_dirty_reads=ON;
+SELECT @@global.wsrep_dirty_reads;
+@@global.wsrep_dirty_reads
+1
+SET @@global.wsrep_dirty_reads=default;
+SELECT @@global.wsrep_dirty_reads;
+@@global.wsrep_dirty_reads
+0
+
 # invalid values
 SET @@session.wsrep_dirty_reads=NULL;
 ERROR 42000: Variable 'wsrep_dirty_reads' can't be set to the value of 'NULL'
 SET @@session.wsrep_dirty_reads='junk';
 ERROR 42000: Variable 'wsrep_dirty_reads' can't be set to the value of 'junk'
+SET @@global.wsrep_dirty_reads=NULL;
+ERROR 42000: Variable 'wsrep_dirty_reads' can't be set to the value of 'NULL'
+SET @@global.wsrep_dirty_reads='junk';
+ERROR 42000: Variable 'wsrep_dirty_reads' can't be set to the value of 'junk'
 
 # restore the initial values
 SET @@session.wsrep_dirty_reads = @wsrep_dirty_reads_session_saved;

mysql-test/suite/sys_vars/t/wsrep_dirty_reads_basic.test

@@ -8,12 +8,12 @@
 SET @wsrep_dirty_reads_session_saved = @@session.wsrep_dirty_reads;
 
 --echo # default
---error ER_INCORRECT_GLOBAL_LOCAL_VAR
+
 SELECT @@global.wsrep_dirty_reads;
 SELECT @@session.wsrep_dirty_reads;
 
 --echo
---echo # scope and valid values
+--echo # valid values for session
 SET @@session.wsrep_dirty_reads=OFF;
 SELECT @@session.wsrep_dirty_reads;
 SET @@session.wsrep_dirty_reads=ON;
@@ -21,12 +21,25 @@ SELECT @@session.wsrep_dirty_reads;
 SET @@session.wsrep_dirty_reads=default;
 SELECT @@session.wsrep_dirty_reads;
 
+--echo
+--echo # valid values for global
+SET @@global.wsrep_dirty_reads=OFF;
+SELECT @@global.wsrep_dirty_reads;
+SET @@global.wsrep_dirty_reads=ON;
+SELECT @@global.wsrep_dirty_reads;
+SET @@global.wsrep_dirty_reads=default;
+SELECT @@global.wsrep_dirty_reads;
+
 --echo
 --echo # invalid values
 --error ER_WRONG_VALUE_FOR_VAR
 SET @@session.wsrep_dirty_reads=NULL;
 --error ER_WRONG_VALUE_FOR_VAR
 SET @@session.wsrep_dirty_reads='junk';
+--error ER_WRONG_VALUE_FOR_VAR
+SET @@global.wsrep_dirty_reads=NULL;
+--error ER_WRONG_VALUE_FOR_VAR
+SET @@global.wsrep_dirty_reads='junk';
 
 --echo
 --echo # restore the initial values

sql/sql_parse.cc

@@ -2649,13 +2649,16 @@ mysql_execute_command(THD *thd)
     }
 
     /*
-      Bail out if DB snapshot has not been installed. We however, allow SET,
-      SHOW and SELECT queries (only if wsrep_dirty_reads is set).
+      Bail out if DB snapshot has not been installed. SET and SHOW commands,
+      however, are always allowed.
+
+      We additionally allow all other commands that do not change data in
+      case wsrep_dirty_reads is enabled.
     */
     if (lex->sql_command != SQLCOM_SET_OPTION  &&
         !wsrep_is_show_query(lex->sql_command) &&
         !(thd->variables.wsrep_dirty_reads     &&
-          lex->sql_command == SQLCOM_SELECT)   &&
+          !is_update_query(lex->sql_command))  &&
         !wsrep_node_is_ready(thd))
       goto error;
   }

sql/sys_vars.cc

@@ -4976,8 +4976,9 @@ static Sys_var_mybool Sys_wsrep_restart_slave(
        GLOBAL_VAR(wsrep_restart_slave), CMD_LINE(OPT_ARG), DEFAULT(FALSE));
 
 static Sys_var_mybool Sys_wsrep_dirty_reads(
-       "wsrep_dirty_reads", "Do not reject SELECT queries even when the node "
-       "is not ready.", SESSION_ONLY(wsrep_dirty_reads), NO_CMD_LINE,
+       "wsrep_dirty_reads",
+       "Allow reads even when the node is not in the primary component.",
+       SESSION_VAR(wsrep_dirty_reads), CMD_LINE(OPT_ARG),
        DEFAULT(FALSE), NO_MUTEX_GUARD, NOT_IN_BINLOG);
 
 static Sys_var_uint Sys_wsrep_gtid_domain_id(

sql/wsrep_mysqld.cc

@@ -96,6 +96,8 @@ bool wsrep_new_cluster                 = false; // Bootstrap the cluster ?
 bool wsrep_gtid_mode                   = 0;
 // gtid_domain_id for galera transactions.
 uint32 wsrep_gtid_domain_id            = 0;
+// Allow reads even if the node is not in the primary component.
+bool wsrep_dirty_reads                 = false;
 
 /*
  * End configuration options
@@ -958,6 +960,8 @@ bool wsrep_must_sync_wait (THD* thd, uint mask)
 {
   return (thd->variables.wsrep_sync_wait & mask) &&
     thd->variables.wsrep_on &&
+    !(thd->variables.wsrep_dirty_reads &&
+      !is_update_query(thd->lex->sql_command)) &&
     !thd->in_active_multi_stmt_transaction() &&
     thd->wsrep_conflict_state != REPLAYING &&
     thd->wsrep_sync_wait_gtid.seqno == WSREP_SEQNO_UNDEFINED;

sql/wsrep_mysqld.h

@@ -89,6 +89,7 @@ extern ulong       wsrep_running_threads;
 extern bool        wsrep_new_cluster;
 extern bool        wsrep_gtid_mode;
 extern uint32      wsrep_gtid_domain_id;
+extern bool        wsrep_dirty_reads;
 
 enum enum_wsrep_OSU_method {
     WSREP_OSU_TOI,