Fix JSON parsing: future-proof data representation in JSON, code cleanup

include/json_lib.h

@@ -283,12 +283,13 @@ int json_key_matches(json_engine_t *je, json_string_t *k);
 int json_read_value(json_engine_t *j);
 
 /*
- * json_smart_read_value() reads parses a scalar value and value length from the json engine,
- * and copies them into `value` and `value_length` respectively.
- * It should only be called when the json_engine state is JST_VALUE.
- * If it encounters a non-scalar value (say object or array) before getting to value_len,
- * such value is also read and copied into value.
- */
+  json_smart_read_value() reads a JSON value. Pointer to value is stored in
+  *value and its length in *value_len.
+
+  if the value is non a scalar, it returns pointers to its JSON
+  representation.
+  The function should only be called when je->state==JST_VALUE.
+*/
 enum json_types json_smart_read_value(json_engine_t *je, const char **value, int *value_len);
 
 /*

mysql-test/main/statistics_json.test

@@ -37,6 +37,8 @@ analyze select * from t1_json where a between 'a-3a' and 'zzzzzzzzz';
 explain extended select * from t1_json where a < 'b-1a';
 analyze select * from t1_json where a > 'zzzzzzzzz';
 
+drop table ten;
+
 # test different valid JSON strings that are invalid histograms.
 UPDATE mysql.column_stats SET histogram='["a-1", "a-2", {"a": "b"}, "a-3"]' WHERE table_name='t1_json';
 FLUSH TABLES;
@@ -45,23 +47,23 @@ explain extended select * from t1_json where a between 'a-3a' and 'zzzzzzzzz';
 
 
 --source include/have_sequence.inc
-create table users (
+create table t2 (
   city varchar(100)
 );
 set histogram_size=50;
-insert into users select 'Moscow' from seq_1_to_99;
-insert into users select 'Helsinki' from seq_1_to_2;
+insert into t2 select 'Moscow' from seq_1_to_99;
+insert into t2 select 'Helsinki' from seq_1_to_2;
 set histogram_type=json_hb;
-analyze table users persistent for all;
-explain extended select * from users where city = 'Moscow';
-analyze select * from users where city = 'Moscow';
-explain extended select * from users where city = 'Helsinki';
-analyze select * from users where city = 'helsinki';
-explain extended select * from users where city < 'Lagos';
+analyze table t2 persistent for all;
+explain extended select * from t2 where city = 'Moscow';
+analyze select * from t2 where city = 'Moscow';
+explain extended select * from t2 where city = 'Helsinki';
+analyze select * from t2 where city = 'helsinki';
+explain extended select * from t2 where city < 'Lagos';
 
 drop table t1_bin;
 drop table t1_json;
-drop table users;
+drop table t2;
 
 DELETE FROM mysql.column_stats;
 

sql/share/errmsg-utf8.txt

@@ -8914,4 +8914,4 @@ ER_PARTITION_CONVERT_SUBPARTITIONED
 ER_PROVIDER_NOT_LOADED
         eng "MariaDB tried to use the %s, but its provider plugin is not loaded"
 ER_JSON_HISTOGRAM_PARSE_FAILED
-        eng "Failed to parse histogram, encountered JSON_TYPE '%d'."
+        eng "Failed to parse histogram: %s at offset %d."

sql/sql_statistics.cc

@@ -1123,6 +1123,7 @@ class Column_stat: public Stat_table
   void get_stat_values()
   {
     table_field->read_stats->set_all_nulls();
+    // default: hist_type=NULL means there's no histogram
     table_field->read_stats->histogram_type_on_disk= INVALID_HISTOGRAM;
 
     if (table_field->read_stats->min_value)
@@ -1196,7 +1197,10 @@ class Column_stat: public Stat_table
               break;
             }
           case COLUMN_STAT_HISTOGRAM:
-            //TODO: if stat_field->length() == 0 then histogram_type_on_disk is set to INVALID_HISTOGRAM
+            /*
+              Do nothing here: we take the histogram length from the 'histogram'
+              column itself
+            */
             break;
           }
         }
@@ -1245,7 +1249,7 @@ class Column_stat: public Stat_table
       }
       if (!hist->parse(mem_root, table_field,
                        table_field->read_stats->histogram_type_on_disk, 
-                       (const uchar*)val.ptr(), val.length()))
+                       val.ptr(), val.length()))
       {
         table_field->read_stats->histogram_= hist;
         return hist;
@@ -1255,19 +1259,19 @@ class Column_stat: public Stat_table
   }
 };
 
-bool Histogram_binary::parse(MEM_ROOT *mem_root, Field *,
-                             Histogram_type type_arg,
-                             const uchar *ptr_arg, uint size_arg)
+
+bool Histogram_binary::parse(MEM_ROOT *mem_root, Field*,
+                             Histogram_type type_arg, const char *hist_data,
+                             size_t hist_data_len)
 {
-  // Just copy the data
-  size = (uint8) size_arg;
-  type = type_arg;
-  if ((values = (uchar*)alloc_root(mem_root, size_arg)))
-  {
-    memcpy(values, ptr_arg, size_arg);
-    return false;
-  }
+  /* On-disk an in-memory formats are the same. Just copy the data. */
+  type= type_arg;
+  size= (uint8) hist_data_len; // 'size' holds the size of histogram in bytes
+  if (!(values= (uchar*)alloc_root(mem_root, hist_data_len)))
     return true;
+
+  memcpy(values, hist_data, hist_data_len);
+  return false;
 }
 
 /*
@@ -1307,39 +1311,81 @@ void Histogram_json::init_for_collection(MEM_ROOT *mem_root,
 */
 
 bool Histogram_json::parse(MEM_ROOT *mem_root, Field *field,
-                           Histogram_type type_arg, const uchar *ptr,
-                           uint size_arg)
+                           Histogram_type type_arg, const char *hist_data,
+                           size_t hist_data_len)
 {
   DBUG_ENTER("Histogram_json::parse");
   DBUG_ASSERT(type_arg == JSON_HB);
-  size = (uint8) size_arg;
-  const char *json = (char *)ptr;
-  int vt;
-  std::vector<std::string> hist_buckets_text;
-  bool result = json_get_array_items(json, json + strlen(json), &vt, hist_buckets_text);
-  if (!result)
-  {
-    my_error(ER_JSON_HISTOGRAM_PARSE_FAILED, MYF(0), vt);
-    DBUG_RETURN(true);
+  const char *err;
+  json_engine_t je;
+  json_string_t key_name;
+
+  json_scan_start(&je, &my_charset_utf8mb4_bin,
+                  (const uchar*)hist_data,
+                  (const uchar*)hist_data+hist_data_len);
+
+  if (json_read_value(&je) || je.value_type != JSON_VALUE_OBJECT)
+  {
+    err= "Root JSON element must be a JSON object";
+    goto error;
   }
-  size= hist_buckets_text.size();
 
-  /*
-    Convert the text based array into a data structure that allows lookups and
-    estimates
-  */
-  for (auto &s : hist_buckets_text)
+  json_string_set_str(&key_name, (const uchar*)JSON_NAME,
+                      (const uchar*)JSON_NAME + strlen(JSON_NAME));
+  json_string_set_cs(&key_name, system_charset_info);
+
+  if (json_scan_next(&je) || je.state != JST_KEY ||
+      !json_key_matches(&je, &key_name))
   {
-    field->store_text(s.data(), s.size(), &my_charset_bin);
+    err= "The first key in the object must be histogram_hb_v1";
+    goto error;
+  }
 
-    // Get the value in "truncated key tuple format" here:
+  // The value must be a JSON array
+  if (json_read_value(&je) || (je.value_type != JSON_VALUE_ARRAY))
+  {
+    err= "A JSON array expected";
+    goto error;
+  }
+
+  // Read the array
+  while (!json_scan_next(&je))
+  {
+    switch(je.state)
+    {
+      case JST_VALUE:
+      {
+        const char *val;
+        int val_len;
+        json_smart_read_value(&je, &val, &val_len);
+        if (je.value_type != JSON_VALUE_STRING &&
+            je.value_type != JSON_VALUE_NUMBER &&
+            je.value_type != JSON_VALUE_TRUE &&
+            je.value_type != JSON_VALUE_FALSE)
+        {
+          err= "Scalar value expected";
+          goto error;
+        }
         uchar buf[MAX_KEY_LENGTH];
         uint len_to_copy= field->key_length();
+        field->store_text(val, val_len, &my_charset_bin);
         uint bytes= field->get_key_image(buf, len_to_copy, Field::itRAW);
         histogram_bounds.push_back(std::string((char*)buf, bytes));
+        // TODO: Should we also compare this endpoint with the previous
+        // to verify that the ordering is right?
+        break;
       }
-
+      case JST_ARRAY_END:
+        break;
+    }
+  }
+  size= histogram_bounds.size();
   DBUG_RETURN(false);
+
+error:
+  my_error(ER_JSON_HISTOGRAM_PARSE_FAILED, MYF(0), err,
+           je.s.c_str - (const uchar*)hist_data);
+  DBUG_RETURN(true);
 }
 
 
@@ -1594,7 +1640,7 @@ double Histogram_json::range_selectivity(Field *field, key_range *min_endp,
 
 void Histogram_json::serialize(Field *field)
 {
-  field->store((char*)json_text, strlen((char*)json_text), &my_charset_bin);
+  field->store(json_text.data(), json_text.size(), &my_charset_bin);
 }
 
 
@@ -2052,13 +2098,16 @@ class Histogram_builder_json : public Histogram_builder
   }
 
   void build_json_from_histogram() {
-    Json_writer *writer = new Json_writer();
-    writer->start_array();
+    Json_writer writer;
+    writer.start_object();
+    writer.add_member(Histogram_json::JSON_NAME).start_array();
+
     for(auto& value: bucket_bounds) {
-      writer->add_str(value.c_str());
+      writer.add_str(value.c_str());
     }
-    writer->end_array();
-    Binary_string *json_string = (Binary_string *) writer->output.get_string();
+    writer.end_array();
+    writer.end_object();
+    Binary_string *json_string = (Binary_string *) writer.output.get_string();
     Histogram_json *hist= (Histogram_json*)histogram;
     hist->set_json_text(bucket_bounds.size(), (uchar *) json_string->c_ptr());
   }
@@ -2080,42 +2129,6 @@ Histogram_base *create_histogram(Histogram_type hist_type)
 }
 
 
-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;
-  const char *v;
-
-  json_scan_start(&je, &my_charset_utf8mb4_bin, (const uchar *)json, (const uchar *)json_end);
-
-  if (json_read_value(&je) || (*value_type = je.value_type) != JSON_VALUE_ARRAY)
-  {
-    return false;
-  }
-
-  std::string val;
-  while(!json_scan_next(&je))
-  {
-    switch(je.state)
-    {
-    case JST_VALUE:
-      *value_type = json_smart_read_value(&je, &v, &vl);
-      if (je.value_type != JSON_VALUE_STRING &&
-          je.value_type != JSON_VALUE_NUMBER &&
-          je.value_type != JSON_VALUE_TRUE &&
-          je.value_type != JSON_VALUE_FALSE)
-      {
-        return false;
-      }
-      val = std::string(v, vl);
-      container.emplace_back(val);
-      break;
-    case JST_ARRAY_END:
-      break;
-    }
-  }
-  return true;
-}
-
 C_MODE_START
 
 int histogram_build_walk(void *elem, element_count elem_cnt, void *arg)

sql/sql_statistics.h

@@ -152,7 +152,7 @@ class Histogram_base : public Sql_alloc
 {
 public:
   virtual bool parse(MEM_ROOT *mem_root, Field *field, Histogram_type type_arg,
-                     const uchar *ptr, uint size)= 0;
+                     const char *hist_data, size_t hist_data_len)= 0;
   virtual void serialize(Field *to_field)= 0;
 
   virtual Histogram_type get_type()=0;
@@ -187,7 +187,7 @@ class Histogram_binary : public Histogram_base
 {
 public:
   bool parse(MEM_ROOT *mem_root, Field *, Histogram_type type_arg, 
-             const uchar *ptr_arg, uint size_arg) override;
+             const char *hist_data, size_t hist_data_len) override;
   void serialize(Field *to_field) override;
 
   Histogram_type get_type() override { return type; }
@@ -350,14 +350,16 @@ class Histogram_json : public Histogram_base
   uint8 size; /* Number of elements in the histogram */
   
   /* Collection-time only: collected histogram in the JSON form. */
-  uchar *json_text;
+  std::string json_text;
 
   // Array of histogram bucket endpoints in KeyTupleFormat.
   std::vector<std::string> histogram_bounds;
 
 public:
+  static constexpr const char* JSON_NAME="histogram_hb_v1";
+
   bool parse(MEM_ROOT *mem_root, Field *field, Histogram_type type_arg,
-             const uchar *ptr, uint size) override;
+             const char *hist_data, size_t hist_data_len) override;
 
   void serialize(Field *field) override;
 
@@ -375,7 +377,8 @@ class Histogram_json : public Histogram_base
   void set_json_text(ulonglong sz, uchar *json_text_arg)
   {
     size = (uint8) sz;
-    json_text= json_text_arg;
+    json_text.assign((const char*)json_text_arg, 
+                     strlen((const char*)json_text_arg));
   }
 
   uint get_size() override
@@ -481,8 +484,9 @@ class Column_statistics
   ulonglong avg_frequency;
 
 public:
-
+  /* Histogram type as specified in mysql.column_stats.hist_type */
   Histogram_type histogram_type_on_disk;
+
   Histogram_base *histogram_;
 
   uint32 no_values_provided_bitmap()