Bug#30087 Set query_cache_size, if the value is too small, get a unclear warning

  
This bugs clarifies a warning message issued when the query cache data
size becomes smaller than the minium allowed size.

1 files changed, 29 insertions, 0 deletions

diff --git a/sql/sql_cache.cc b/sql/sql_cache.cc
index f8906a17c12..cce5123aef3 100644
--- a/sql/sql_cache.cc
+++ b/sql/sql_cache.cc
@@ -816,6 +816,16 @@ ulong Query_cache::resize(ulong query_cache_size_arg)
   free_cache();
   query_cache_size= query_cache_size_arg;
   ::query_cache_size= init_cache();
+
+  if (::query_cache_size != query_cache_size_arg)
+  {
+    push_warning_printf(current_thd, MYSQL_ERROR::WARN_LEVEL_WARN,
+                        ER_WARN_QC_RESIZE, ER(ER_WARN_QC_RESIZE),
+                        query_cache_size_arg,
+                        get_minimal_size_limit(),
+                        ::query_cache_size);
+  }
+
   STRUCT_UNLOCK(&structure_guard_mutex);
   DBUG_RETURN(::query_cache_size);
 }
@@ -1614,6 +1624,25 @@ void Query_cache::init()
 }
 
 
+/**
+  Return the lowest possible query cache size.
+*/
+
+ulong Query_cache::get_minimal_size_limit()
+{
+  ulong approx_additional_data_size= (sizeof(Query_cache) +
+                                      sizeof(gptr)*(def_query_hash_size+
+                                      def_table_hash_size));
+
+  ulong data_size= (min_allocation_unit << QUERY_CACHE_MEM_BIN_STEP_PWR2 <<
+                    QUERY_CACHE_MEM_BIN_FIRST_STEP_PWR2) +
+                    ALIGN_SIZE(1) - 1 +
+                    (1 << QUERY_CACHE_MEM_BIN_STEP_PWR2) - 1 +
+                    (1 << QUERY_CACHE_MEM_BIN_FIRST_STEP_PWR2) - 1;
+
+  return(data_size + approx_additional_data_size);
+}
+
 ulong Query_cache::init_cache()
 {
   uint mem_bin_count, num, step;