Merge damien-katzs-computer.local:/Users/dkatz/mysql50

into  damien-katzs-computer.local:/Users/dkatz/50b

mysql-test/r/variables-big.result

+set session transaction_prealloc_size=1024*1024*1024*1;
+show processlist;
+Id	User	Host	db	Command	Time	State	Info
+1	root	localhost	test	Query	0	NULL	show processlist
+set session transaction_prealloc_size=1024*1024*1024*2;
+show processlist;
+Id	User	Host	db	Command	Time	State	Info
+1	root	localhost	test	Query	2	NULL	show processlist
+set session transaction_prealloc_size=1024*1024*1024*3;
+show processlist;
+Id	User	Host	db	Command	Time	State	Info
+1	root	localhost	test	Query	0	NULL	show processlist
+set session transaction_prealloc_size=1024*1024*1024*4;
+show processlist;
+Id	User	Host	db	Command	Time	State	Info
+1	root	localhost	test	Query	0	NULL	show processlist
+set session transaction_prealloc_size=1024*1024*1024*5;
+show processlist;
+Id	User	Host	db	Command	Time	State	Info
+1	root	localhost	test	Query	0	NULL	show processlist

mysql-test/t/variables-big.test

+#
+# test variables big
+#
+
+--source include/big_test.inc
+
+#
+# Bug #27322  	failure to allocate transaction_prealloc_size causes crash
+#
+
+set session transaction_prealloc_size=1024*1024*1024*1;
+show processlist;
+set session transaction_prealloc_size=1024*1024*1024*2;
+show processlist;
+set session transaction_prealloc_size=1024*1024*1024*3;
+show processlist;
+set session transaction_prealloc_size=1024*1024*1024*4;
+show processlist;
+set session transaction_prealloc_size=1024*1024*1024*5;
+show processlist;

mysys/my_alloc.c

@@ -133,6 +133,10 @@ void reset_root_defaults(MEM_ROOT *mem_root, uint block_size,
         mem->next= *prev;
         *prev= mem_root->pre_alloc= mem; 
       }
+      else
+      {
+        mem_root->pre_alloc= 0;
+      }
     }
   }
   else