fixed bug 549 - incorect query cache memory formating on very small query cache sizes

mysql-test/r/query_cache.result:
  test of 2 parts of bug 549
mysql-test/t/query_cache.test:
  test of 2 parts of bug 549
sql/sql_cache.cc:
  fixed query cache size showing
  fixed query cache low memory detection

mysql-test/r/query_cache.result

@@ -501,22 +501,62 @@ drop table t1;
 show status like "Qcache_queries_in_cache";
 Variable_name	Value
 Qcache_queries_in_cache	0
+create table t1 (a int);
 set GLOBAL query_cache_size=1000;
 show global variables like "query_cache_size";
 Variable_name	Value
 query_cache_size	0
-set GLOBAL query_cache_size=1100;
-set GLOBAL query_cache_size=1200;
-set GLOBAL query_cache_size=1300;
-set GLOBAL query_cache_size=1400;
-set GLOBAL query_cache_size=1500;
-set GLOBAL query_cache_size=1600;
-set GLOBAL query_cache_size=1700;
-set GLOBAL query_cache_size=1800;
-set GLOBAL query_cache_size=1900;
+select * from t1;
+a
+set GLOBAL query_cache_size=1024;
+show global variables like "query_cache_size";
+Variable_name	Value
+query_cache_size	0
+select * from t1;
+a
+set GLOBAL query_cache_size=10240;
+show global variables like "query_cache_size";
+Variable_name	Value
+query_cache_size	0
+select * from t1;
+a
+set GLOBAL query_cache_size=20480;
+show global variables like "query_cache_size";
+Variable_name	Value
+query_cache_size	0
+select * from t1;
+a
+set GLOBAL query_cache_size=40960;
+show global variables like "query_cache_size";
+Variable_name	Value
+query_cache_size	0
+select * from t1;
+a
+set GLOBAL query_cache_size=51200;
+show global variables like "query_cache_size";
+Variable_name	Value
+query_cache_size	51200
+select * from t1;
+a
+set GLOBAL query_cache_size=61440;
 show global variables like "query_cache_size";
 Variable_name	Value
-query_cache_size	1024
+query_cache_size	61440
+select * from t1;
+a
+set GLOBAL query_cache_size=81920;
+show global variables like "query_cache_size";
+Variable_name	Value
+query_cache_size	81920
+select * from t1;
+a
+set GLOBAL query_cache_size=102400;
+show global variables like "query_cache_size";
+Variable_name	Value
+query_cache_size	102400
+select * from t1;
+a
+drop table t1;
 set GLOBAL query_cache_size=1048576;
 create table t1 (i int not null);
 create table t2 (i int not null);

mysql-test/t/query_cache.test

@@ -343,18 +343,35 @@ show status like "Qcache_queries_in_cache";
 #
 # Test of query cache resizing
 #
+create table t1 (a int);
 set GLOBAL query_cache_size=1000;
 show global variables like "query_cache_size";
-set GLOBAL query_cache_size=1100;
-set GLOBAL query_cache_size=1200;
-set GLOBAL query_cache_size=1300;
-set GLOBAL query_cache_size=1400;
-set GLOBAL query_cache_size=1500;
-set GLOBAL query_cache_size=1600;
-set GLOBAL query_cache_size=1700;
-set GLOBAL query_cache_size=1800;
-set GLOBAL query_cache_size=1900;
+select * from t1;
+set GLOBAL query_cache_size=1024;
+show global variables like "query_cache_size";
+select * from t1;
+set GLOBAL query_cache_size=10240;
+show global variables like "query_cache_size";
+select * from t1;
+set GLOBAL query_cache_size=20480;
+show global variables like "query_cache_size";
+select * from t1;
+set GLOBAL query_cache_size=40960;
+show global variables like "query_cache_size";
+select * from t1;
+set GLOBAL query_cache_size=51200;
+show global variables like "query_cache_size";
+select * from t1;
+set GLOBAL query_cache_size=61440;
+show global variables like "query_cache_size";
+select * from t1;
+set GLOBAL query_cache_size=81920;
 show global variables like "query_cache_size";
+select * from t1;
+set GLOBAL query_cache_size=102400;
+show global variables like "query_cache_size";
+select * from t1;
+drop table t1;
 
 #
 # Temporary tables

sql/sql_cache.cc

@@ -731,7 +731,7 @@ ulong Query_cache::resize(ulong query_cache_size_arg)
 			query_cache_size_arg));
   free_cache(0);
   query_cache_size= query_cache_size_arg;
-  DBUG_RETURN(init_cache());
+  DBUG_RETURN(::query_cache_size= init_cache());
 }
 
 
@@ -1282,6 +1282,12 @@ ulong Query_cache::init_cache()
   mem_bin_steps = 1;
   mem_bin_size = max_mem_bin_size >> QUERY_CACHE_MEM_BIN_STEP_PWR2;
   prev_size = 0;
+  if (mem_bin_size <= min_allocation_unit)
+  {
+    DBUG_PRINT("qcache", ("too small query cache => query cache disabled"));
+    // TODO here (and above) should be warning in 4.1
+    goto err;
+  }
   while (mem_bin_size > min_allocation_unit)
   {
     mem_bin_num += mem_bin_count;
@@ -1308,14 +1314,6 @@ ulong Query_cache::init_cache()
   query_cache_size -= additional_data_size;
 
   STRUCT_LOCK(&structure_guard_mutex);
-  if (max_mem_bin_size	<= min_allocation_unit)
-  {
-    DBUG_PRINT("qcache",
-	       (" max bin size (%lu) <= min_allocation_unit => cache disabled",
-		max_mem_bin_size));
-    STRUCT_UNLOCK(&structure_guard_mutex);
-    goto err;
-  }
 
   if (!(cache = (byte *)
 	 my_malloc_lock(query_cache_size+additional_data_size, MYF(0))))