Code cleanup part #2.

Author: spetrunia

sql/sql_statistics.cc

@@ -1292,8 +1292,7 @@ void Histogram_json::init_for_collection(MEM_ROOT *mem_root,
                                          Histogram_type htype_arg,
                                          ulonglong size_arg)
 {
-  type= htype_arg;
-  //values_ = (uchar*)alloc_root(mem_root, size_arg);
+  DBUG_ASSERT(htype_arg == JSON_HB);
   size= (uint8) size_arg;
 }
 
@@ -1302,15 +1301,18 @@ void Histogram_json::init_for_collection(MEM_ROOT *mem_root,
   @brief
     Parse the histogram from its on-disk representation
 
+  @return
+     false  OK
+     True   Error
 */
 
 bool Histogram_json::parse(MEM_ROOT *mem_root, Field *field,
                            Histogram_type type_arg, const uchar *ptr,
                            uint size_arg)
 {
   DBUG_ENTER("Histogram_json::parse");
+  DBUG_ASSERT(type_arg == JSON_HB);
   size = (uint8) size_arg;
-  type = type_arg;
   const char *json = (char *)ptr;
   int vt;
   std::vector<std::string> hist_buckets_text;
@@ -1595,6 +1597,7 @@ void Histogram_json::serialize(Field *field)
   field->store((char*)json_text, strlen((char*)json_text), &my_charset_bin);
 }
 
+
 int Histogram_json::find_bucket(Field *field, const uchar *endpoint)
 {
   int low = 0;
@@ -2061,15 +2064,22 @@ class Histogram_builder_json : public Histogram_builder
   }
 };
 
+
 Histogram_base *create_histogram(Histogram_type hist_type)
 {
-  // assumes the caller already checked for invalid histograms
-  if (hist_type == JSON_HB)
-    return new Histogram_json;
-  else
-    return new Histogram_binary;
+  switch (hist_type) {
+  case SINGLE_PREC_HB:
+  case DOUBLE_PREC_HB:
+    return new Histogram_binary();
+  case JSON_HB:
+    return new Histogram_json();
+  default:
+    DBUG_ASSERT(0);
+  }
+  return NULL;
 }
 
+
 bool json_get_array_items(const char *json, const char *json_end, int *value_type, std::vector<std::string> &container) {
   json_engine_t je;
   int vl;
@@ -2255,16 +2265,6 @@ class Count_distinct_field: public Sql_alloc
     return distincts_single_occurence;
   }
 
-  /*
-    @brief
-    Get the size of the histogram in bytes built for table_field
-  */
-  /*
-  uint get_hist_size()
-  {
-    return table_field->collected_stats->histogram.get_size();
-  }*/
-
   /*
     @brief
     Get the pointer to the histogram built for table_field
@@ -2916,27 +2916,6 @@ bool Column_statistics_collected::add()
   return err;
 }
 
-
-/* 
-  Create an empty Histogram object from histogram_type.
-
-  Note: it is not yet clear whether collection-time histogram should be the same 
-  as lookup-time histogram. At the moment, they are.
-*/
-
-Histogram_base * get_histogram_by_type(MEM_ROOT *mem_root, Histogram_type hist_type) {
-  switch (hist_type) {
-  case SINGLE_PREC_HB:
-  case DOUBLE_PREC_HB:
-    return new Histogram_binary();
-  case JSON_HB:
-    return new Histogram_json();
-  default:
-    DBUG_ASSERT(0);
-  }
-  return NULL;
-};
-
 /**
   @brief
   Get the results of aggregation when collecting the statistics on a column
@@ -3488,15 +3467,13 @@ int read_statistics_for_table(THD *thd, TABLE *table, TABLE_LIST *stat_tables)
 
   /* Read statistics from the statistical table column_stats */
   stat_table= stat_tables[COLUMN_STAT].table;
-  //ulong total_hist_size= 0;
   bool have_histograms= false;
   Column_stat column_stat(stat_table, table);
   for (field_ptr= table_share->field; *field_ptr; field_ptr++)
   {
     table_field= *field_ptr;
     column_stat.set_key_fields(table_field);
     column_stat.get_stat_values();
-    //total_hist_size+= table_field->read_stats->histogram.get_size();
     if (table_field->read_stats->histogram_type_on_disk != INVALID_HISTOGRAM)
       have_histograms= true;
   }

sql/sql_statistics.h

@@ -17,6 +17,8 @@
 #define SQL_STATISTICS_H
 
 #include <vector>
+#include <string>
+
 /*
   For COMPLEMENTARY_FOR_QUERIES and PREFERABLY_FOR_QUERIES they are
   similar to the COMPLEMENTARY and PREFERABLY respectively except that
@@ -279,7 +281,7 @@ class Histogram_binary : public Histogram_base
 
   uint get_size() override {return (uint)size;}
 
-  bool is_available() override { return get_size() > 0 && (values!=NULL); }
+  bool is_available() override { return (values!=NULL); }
 
   /*
     This function checks that histograms should be usable only when
@@ -335,13 +337,17 @@ class Histogram_binary : public Histogram_base
 
 /*
   An equi-height histogram which stores real values for bucket bounds.
+
+  Handles @@histogram_type=JSON_HB
+
+  On-disk format is JSON:
+   (TODO description)
 */
 
 class Histogram_json : public Histogram_base
 {
 private:
-  Histogram_type type;
-  uint8 size; /* Number of elements in the histogram*/
+  uint8 size; /* Number of elements in the histogram */
 
   /* Collection-time only: collected histogram in the JSON form. */
   uchar *json_text;
@@ -414,7 +420,6 @@ class Table_statistics
 
   /* Array of records per key for index prefixes */
   ulonglong *idx_avg_frequency;
-  //uchar *histograms;                /* Sequence of histograms       */
 };