MDEV-6500: Stale data returned after TRUNCATE PARTITION operation

When truncating a table's partition, we also need to invalidate the
query cache for it.

mysql-test/r/truncate-stale-6500.result

+SET GLOBAL query_cache_size=1024*1024*8;
+CREATE TABLE `test` (
+`uniqueId` INT NOT NULL,
+`partitionId` INT NOT NULL,
+PRIMARY KEY (`uniqueId`,`partitionId`)
+) ENGINE=InnoDB PARTITION BY LIST (partitionId) (
+PARTITION p01 VALUES IN (1),
+PARTITION p02 VALUES IN (2)
+);
+INSERT INTO `test`(`uniqueId`,`partitionId`) VALUES(407237055, 2);
+SELECT * FROM `test`;
+uniqueId	partitionId
+407237055	2
+#Confirms 1 row in partition 'p02'
+SELECT TABLE_NAME, PARTITION_NAME, TABLE_ROWS FROM information_schema.PARTITIONS where TABLE_NAME = 'test';
+TABLE_NAME	PARTITION_NAME	TABLE_ROWS
+test	p01	0
+test	p02	1
+ALTER TABLE `test` TRUNCATE PARTITION `p02`;
+#Confirms no more rows in partition 'p02'
+SELECT TABLE_NAME, PARTITION_NAME, TABLE_ROWS FROM information_schema.PARTITIONS where TABLE_NAME = 'test';
+TABLE_NAME	PARTITION_NAME	TABLE_ROWS
+test	p01	0
+test	p02	0
+#Before the patch, this returned the previously existing values.
+SELECT * FROM `test`;
+uniqueId	partitionId
+SELECT SQL_CACHE * FROM `test`;
+uniqueId	partitionId
+SELECT SQL_NO_CACHE * FROM `test`;
+uniqueId	partitionId
+DROP TABLE test;
+SET GLOBAL query_cache_size=DEFAULT;

mysql-test/t/truncate-stale-6500.test

+--source include/have_innodb.inc
+--source include/have_partition.inc
+
+SET GLOBAL query_cache_size=1024*1024*8;
+CREATE TABLE `test` (
+  `uniqueId` INT NOT NULL,
+  `partitionId` INT NOT NULL,
+  PRIMARY KEY (`uniqueId`,`partitionId`)
+) ENGINE=InnoDB PARTITION BY LIST (partitionId) (
+ PARTITION p01 VALUES IN (1),
+ PARTITION p02 VALUES IN (2)
+);
+
+
+INSERT INTO `test`(`uniqueId`,`partitionId`) VALUES(407237055, 2);
+
+SELECT * FROM `test`;
+
+--echo #Confirms 1 row in partition 'p02'
+SELECT TABLE_NAME, PARTITION_NAME, TABLE_ROWS FROM information_schema.PARTITIONS where TABLE_NAME = 'test';
+ALTER TABLE `test` TRUNCATE PARTITION `p02`;
+
+--echo #Confirms no more rows in partition 'p02'
+SELECT TABLE_NAME, PARTITION_NAME, TABLE_ROWS FROM information_schema.PARTITIONS where TABLE_NAME = 'test';
+
+--echo #Before the patch, this returned the previously existing values.
+SELECT * FROM `test`;
+SELECT SQL_CACHE * FROM `test`;
+SELECT SQL_NO_CACHE * FROM `test`;
+
+DROP TABLE test;
+SET GLOBAL query_cache_size=DEFAULT;

sql/sql_partition_admin.cc

@@ -174,9 +174,16 @@ bool Alter_table_truncate_partition_statement::execute(THD *thd)
     log. The exception is a unimplemented truncate method or failure
     before any call to handler::truncate() is done.
     Also, it is logged in statement format, regardless of the binlog format.
+
+    Since we've changed data within the table, we also have to invalidate
+    the query cache for it.
   */
-  if (error != HA_ERR_WRONG_COMMAND && binlog_stmt)
+  if (error != HA_ERR_WRONG_COMMAND)
+  {
+    query_cache_invalidate3(thd, first_table, FALSE);
+    if (binlog_stmt)
       error|= write_bin_log(thd, !error, thd->query(), thd->query_length());
+  }
 
   /*
     A locked table ticket was upgraded to a exclusive lock. After the