Prepare JSON as valid histogram_type

Signed-off-by: Michael Okoko <okokomichaels@outlook.com>

scripts/mysql_system_tables.sql

@@ -314,7 +314,7 @@ DROP TABLE tmp_proxies_priv;
 
 CREATE TABLE IF NOT EXISTS table_stats (db_name varchar(64) NOT NULL, table_name varchar(64) NOT NULL, cardinality bigint(21) unsigned DEFAULT NULL, PRIMARY KEY (db_name,table_name) ) engine=Aria transactional=0 CHARACTER SET utf8 COLLATE utf8_bin comment='Statistics on Tables';
 
-CREATE TABLE IF NOT EXISTS column_stats (db_name varchar(64) NOT NULL, table_name varchar(64) NOT NULL, column_name varchar(64) NOT NULL, min_value varbinary(255) DEFAULT NULL, max_value varbinary(255) DEFAULT NULL, nulls_ratio decimal(12,4) DEFAULT NULL, avg_length decimal(12,4) DEFAULT NULL, avg_frequency decimal(12,4) DEFAULT NULL, hist_size tinyint unsigned, hist_type enum('SINGLE_PREC_HB','DOUBLE_PREC_HB'), histogram varbinary(255), PRIMARY KEY (db_name,table_name,column_name) ) engine=Aria transactional=0 CHARACTER SET utf8 COLLATE utf8_bin comment='Statistics on Columns';
+CREATE TABLE IF NOT EXISTS column_stats (db_name varchar(64) NOT NULL, table_name varchar(64) NOT NULL, column_name varchar(64) NOT NULL, min_value varbinary(255) DEFAULT NULL, max_value varbinary(255) DEFAULT NULL, nulls_ratio decimal(12,4) DEFAULT NULL, avg_length decimal(12,4) DEFAULT NULL, avg_frequency decimal(12,4) DEFAULT NULL, hist_size tinyint unsigned, hist_type enum('SINGLE_PREC_HB','DOUBLE_PREC_HB','JSON'), histogram varbinary(255), PRIMARY KEY (db_name,table_name,column_name) ) engine=Aria transactional=0 CHARACTER SET utf8 COLLATE utf8_bin comment='Statistics on Columns';
 
 CREATE TABLE IF NOT EXISTS index_stats (db_name varchar(64) NOT NULL, table_name varchar(64) NOT NULL, index_name varchar(64) NOT NULL, prefix_arity int(11) unsigned NOT NULL, avg_frequency decimal(12,4) DEFAULT NULL, PRIMARY KEY (db_name,table_name,index_name,prefix_arity) ) engine=Aria transactional=0 CHARACTER SET utf8 COLLATE utf8_bin comment='Statistics on Indexes';
 

sql/item_strfunc.cc

@@ -503,7 +503,7 @@ String *Item_func_from_base64::val_str(String *str)
 
 
 const char *histogram_types[] =
-           {"SINGLE_PREC_HB", "DOUBLE_PREC_HB", 0};
+    {"SINGLE_PREC_HB", "DOUBLE_PREC_HB", "JSON", 0};
 static TYPELIB histogram_types_typelib=
   { array_elements(histogram_types),
     "histogram_types",

sql/sql_statistics.cc

@@ -178,7 +178,7 @@ TABLE_FIELD_TYPE column_stat_fields[COLUMN_STAT_N_FIELDS] =
   },
   {
     { STRING_WITH_LEN("hist_type") },
-    { STRING_WITH_LEN("enum('SINGLE_PREC_HB','DOUBLE_PREC_HB')") },
+    { STRING_WITH_LEN("enum('SINGLE_PREC_HB','DOUBLE_PREC_HB','JSON')") },
     { STRING_WITH_LEN("utf8mb3") }
   },
   {
@@ -1070,8 +1070,12 @@ class Column_stat: public Stat_table
           stat_field->store(stats->histogram.get_type() + 1);
           break;
         case COLUMN_STAT_HISTOGRAM:
-	  stat_field->store((char *)stats->histogram.get_values(),
+          if (stats->histogram.get_type() == JSON) {
+            stat_field->store((char *) "hello_world", 11, &my_charset_bin);
+          } else {
+            stat_field->store((char *) stats->histogram.get_values(),
                               stats->histogram.get_size(), &my_charset_bin);
+          }
           break;           
         }
       }

sql/sql_statistics.h

@@ -42,7 +42,8 @@ typedef
 enum enum_histogram_type
 {
   SINGLE_PREC_HB,
-  DOUBLE_PREC_HB
+  DOUBLE_PREC_HB,
+  JSON
 } Histogram_type;
 
 enum enum_stat_tables
@@ -154,6 +155,7 @@ class Histogram
     case SINGLE_PREC_HB:
       return ((uint) (1 << 8) - 1);
     case DOUBLE_PREC_HB:
+    case JSON:
       return ((uint) (1 << 16) - 1);
     }
     return 1;
@@ -166,6 +168,7 @@ class Histogram
     case SINGLE_PREC_HB:
       return size;
     case DOUBLE_PREC_HB:
+    case JSON:
       return size / 2;
     }
     return 0;
@@ -179,6 +182,7 @@ class Histogram
     case SINGLE_PREC_HB:
       return (uint) (((uint8 *) values)[i]);
     case DOUBLE_PREC_HB:
+    case JSON:
       return (uint) uint2korr(values + i * 2);
     }
     return 0;
@@ -254,6 +258,7 @@ class Histogram
   {
     switch (type) {
     case SINGLE_PREC_HB:
+    case JSON:
       ((uint8 *) values)[i]= (uint8) (val * prec_factor());
       return;
     case DOUBLE_PREC_HB:
@@ -266,6 +271,7 @@ class Histogram
   {
     switch (type) {
     case SINGLE_PREC_HB:
+    case JSON:
       ((uint8 *) values)[i]= ((uint8 *) values)[i-1];
       return;
     case DOUBLE_PREC_HB: