path: root/sql/sql_explain.cc

/*
   Copyright (c) 2013 Monty Program Ab

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; version 2 of the License.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */

#ifdef USE_PRAGMA_IMPLEMENTATION
#pragma implementation				// gcc: Class implementation
#endif

#include "sql_priv.h"
#include "sql_select.h"
#include "my_json_writer.h"

const char * STR_DELETING_ALL_ROWS= "Deleting all rows";
const char * STR_IMPOSSIBLE_WHERE= "Impossible WHERE";
const char * STR_NO_ROWS_AFTER_PRUNING= "No matching rows after partition pruning";

Explain_query::Explain_query(THD *thd_arg) : 
  upd_del_plan(NULL), insert_plan(NULL), thd(thd_arg), apc_enabled(false)
{
  operations= 0;
}


Explain_query::~Explain_query()
{
  if (apc_enabled)
    thd->apc_target.disable();

  delete upd_del_plan;
  delete insert_plan;
  uint i;
  for (i= 0 ; i < unions.elements(); i++)
    delete unions.at(i);
  for (i= 0 ; i < selects.elements(); i++)
    delete selects.at(i);
}


Explain_node *Explain_query::get_node(uint select_id)
{
  Explain_union *u;
  if ((u= get_union(select_id)))
    return u;
  else
    return get_select(select_id);
}

Explain_union *Explain_query::get_union(uint select_id)
{
  return (unions.elements() > select_id) ? unions.at(select_id) : NULL;
}

Explain_select *Explain_query::get_select(uint select_id)
{
  return (selects.elements() > select_id) ? selects.at(select_id) : NULL;
}


void Explain_query::add_node(Explain_node *node)
{
  uint select_id;
  operations++;
  if (node->get_type() == Explain_node::EXPLAIN_UNION)
  {
    Explain_union *u= (Explain_union*)node;
    select_id= u->get_select_id();
    if (unions.elements() <= select_id)
      unions.resize(MY_MAX(select_id+1, unions.elements()*2), NULL);

    Explain_union *old_node;
    if ((old_node= get_union(select_id)))
      delete old_node;

    unions.at(select_id)= u;
  }
  else
  {
    Explain_select *sel= (Explain_select*)node;
    if (sel->select_id == FAKE_SELECT_LEX_ID)
    {
      DBUG_ASSERT(0); // this is a "fake select" from a UNION.
    }
    else
    {
      select_id= sel->select_id;
      Explain_select *old_node;

      if (selects.elements() <= select_id)
        selects.resize(MY_MAX(select_id+1, selects.elements()*2), NULL);

      if ((old_node= get_select(select_id)))
        delete old_node;

      selects.at(select_id)= sel;
    }
  }
}


void Explain_query::add_insert_plan(Explain_insert *insert_plan_arg)
{
  insert_plan= insert_plan_arg;
  query_plan_ready();
}


void Explain_query::add_upd_del_plan(Explain_update *upd_del_plan_arg)
{
  upd_del_plan= upd_del_plan_arg;
  query_plan_ready();
}


void Explain_query::query_plan_ready()
{
  if (!apc_enabled)
    thd->apc_target.enable();
  apc_enabled= true;
}

/*
  Send EXPLAIN output to the client.
*/

int Explain_query::send_explain(THD *thd)
{
  select_result *result;
  LEX *lex= thd->lex;
 
  if (!(result= new select_send()) || 
      thd->send_explain_fields(result, lex->describe, lex->analyze_stmt))
    return 1;

  int res= 0;
  if (thd->lex->explain_json)
    print_explain_json(result, thd->lex->analyze_stmt);
  else
    res= print_explain(result, lex->describe, thd->lex->analyze_stmt);

  if (res)
    result->abort_result_set();
  else
    result->send_eof();

  return res;
}


/*
  The main entry point to print EXPLAIN of the entire query
*/

int Explain_query::print_explain(select_result_sink *output, 
                                 uint8 explain_flags, bool is_analyze)
{
  if (upd_del_plan)
  {
    upd_del_plan->print_explain(this, output, explain_flags, is_analyze);
    return 0;
  }
  else if (insert_plan)
  {
    insert_plan->print_explain(this, output, explain_flags, is_analyze);
    return 0;
  }
  else
  {
    /* Start printing from node with id=1 */
    Explain_node *node= get_node(1);
    if (!node)
      return 1; /* No query plan */
    return node->print_explain(this, output, explain_flags, is_analyze);
  }
}


void Explain_query::print_explain_json(select_result_sink *output, bool is_analyze)
{
  Json_writer writer;
  writer.start_object();

  if (upd_del_plan)
    upd_del_plan->print_explain_json(this, &writer, is_analyze);
  else if (insert_plan)
  {
    //insert_plan->print_explain(this, output, explain_flags, is_analyze);
    DBUG_ASSERT(0);
  }
  else
  {
    /* Start printing from node with id=1 */
    Explain_node *node= get_node(1);
    if (!node)
      return; /* No query plan */
    node->print_explain_json(this, &writer, is_analyze);
  }

  writer.end_object();

  const CHARSET_INFO *cs= system_charset_info;
  List<Item> item_list;
  String *buf= &writer.output;
  item_list.push_back(new Item_string(buf->ptr(), buf->length(), cs));
  output->send_data(item_list);
}


bool print_explain_for_slow_log(LEX *lex, THD *thd, String *str)
{
  return lex->explain->print_explain_str(thd, str, /*is_analyze*/ true);
}


/* 
  Return tabular EXPLAIN output as a text string
*/

bool Explain_query::print_explain_str(THD *thd, String *out_str,  bool is_analyze)
{
  List<Item> fields;
  thd->make_explain_field_list(fields, thd->lex->describe, is_analyze);

  select_result_text_buffer output_buf(thd);
  output_buf.send_result_set_metadata(fields, thd->lex->describe);
  if (print_explain(&output_buf, thd->lex->describe, is_analyze))
    return true;
  output_buf.save_to(out_str);
  return false;
}


static void push_str(List<Item> *item_list, const char *str)
{
  item_list->push_back(new Item_string_sys(str));
}


static void push_string(List<Item> *item_list, String *str)
{
  item_list->push_back(new Item_string_sys(str->ptr(), str->length()));
}

static void push_string_list(List<Item> *item_list, String_list &lines, 
                             String *buf)
{
  List_iterator_fast<char> it(lines);
  char *line;
  bool first= true;
  while ((line= it++))
  {
    if (first)
      first= false;
    else
      buf->append(',');

    buf->append(line);
  }
  push_string(item_list, buf);
}


/*
  Print an EXPLAIN output row, based on information provided in the parameters

  @note
    Parameters that may have NULL value in EXPLAIN output, should be passed
    (char*)NULL.

  @return 
    0  - OK
    1  - OOM Error
*/

static
int print_explain_row(select_result_sink *result,
                      uint8 options, bool is_analyze,
                      uint select_number,
                      const char *select_type,
                      const char *table_name,
                      const char *partitions,
                      enum join_type jtype,
                      String_list *possible_keys,
                      const char *index,
                      const char *key_len,
                      const char *ref,
                      ha_rows *rows,
                      ha_rows *r_rows,
                      double r_filtered,
                      const char *extra)
{
  Item *item_null= new Item_null();
  List<Item> item_list;
  Item *item;

  item_list.push_back(new Item_int((int32) select_number));
  item_list.push_back(new Item_string_sys(select_type));
  item_list.push_back(new Item_string_sys(table_name));
  if (options & DESCRIBE_PARTITIONS)
  {
    if (partitions)
    {
      item_list.push_back(new Item_string_sys(partitions));
    }
    else
      item_list.push_back(item_null);
  }
  
  const char *jtype_str= join_type_str[jtype];
  item_list.push_back(new Item_string_sys(jtype_str));
  
  /* 'possible_keys' */
  if (possible_keys && !possible_keys->is_empty())
  {
    StringBuffer<64> possible_keys_buf;
    push_string_list(&item_list, *possible_keys, &possible_keys_buf);
  }
  else
    item_list.push_back(item_null);
  
  /* 'index */
  item= index ? new Item_string_sys(index) : item_null;
  item_list.push_back(item);
  
  /* 'key_len */
  item= key_len ? new Item_string_sys(key_len) : item_null;
  item_list.push_back(item);
  
  /* 'ref' */
  item= ref ? new Item_string_sys(ref) : item_null;
  item_list.push_back(item);

  /* 'rows' */
  if (rows)
  {
    item_list.push_back(new Item_int(*rows, 
                                     MY_INT64_NUM_DECIMAL_DIGITS));
  }
  else
    item_list.push_back(item_null);
  
  /* 'r_rows' */
  if (is_analyze)
  {
    if (r_rows)
    {
      item_list.push_back(new Item_int(*r_rows, 
                                       MY_INT64_NUM_DECIMAL_DIGITS));
    }
    else
      item_list.push_back(item_null);
  }

  /* 'filtered' */
  const double filtered=100.0;
  if (options & DESCRIBE_EXTENDED || is_analyze)
    item_list.push_back(new Item_float(filtered, 2));
  
  /* 'r_filtered' */
  if (is_analyze)
    item_list.push_back(new Item_float(r_filtered, 2));
  
  /* 'Extra' */
  if (extra)
    item_list.push_back(new Item_string_sys(extra));
  else
    item_list.push_back(item_null);

  if (result->send_data(item_list))
    return 1;
  return 0;
}




uint Explain_union::make_union_table_name(char *buf)
{
  uint childno= 0;
  uint len= 6, lastop= 0;
  memcpy(buf, STRING_WITH_LEN("<union"));

  for (; childno < union_members.elements() && len + lastop + 5 < NAME_LEN;
       childno++)
  {
    len+= lastop;
    lastop= my_snprintf(buf + len, NAME_LEN - len,
                        "%u,", union_members.at(childno));
  }

  if (childno < union_members.elements() || len + lastop >= NAME_LEN)
  {
    memcpy(buf + len, STRING_WITH_LEN("...>") + 1);
    len+= 4;
  }
  else
  {
    len+= lastop;
    buf[len - 1]= '>';  // change ',' to '>'
  }
  return len;
}


int Explain_union::print_explain(Explain_query *query, 
                                 select_result_sink *output,
                                 uint8 explain_flags, 
                                 bool is_analyze)
{
  //const CHARSET_INFO *cs= system_charset_info;
  char table_name_buffer[SAFE_NAME_LEN];

  /* print all UNION children, in order */
  for (int i= 0; i < (int) union_members.elements(); i++)
  {
    Explain_select *sel= query->get_select(union_members.at(i));
    sel->print_explain(query, output, explain_flags, is_analyze);
  }

  if (!using_tmp)
    return 0;

  /* Print a line with "UNION RESULT" */
  List<Item> item_list;
  Item *item_null= new Item_null();

  /* `id` column */
  item_list.push_back(item_null);

  /* `select_type` column */
  push_str(&item_list, fake_select_type);

  /* `table` column: something like "<union1,2>" */
  uint len= make_union_table_name(table_name_buffer);
  item_list.push_back(new Item_string_sys(table_name_buffer, len));
  
  /* `partitions` column */
  if (explain_flags & DESCRIBE_PARTITIONS)
    item_list.push_back(item_null);

  /* `type` column */
  push_str(&item_list, join_type_str[JT_ALL]);

  /* `possible_keys` column */
  item_list.push_back(item_null);

  /* `key` */
  item_list.push_back(item_null);

  /* `key_len` */
  item_list.push_back(item_null);

  /* `ref` */
  item_list.push_back(item_null);
 
  /* `rows` */
  item_list.push_back(item_null);
  
  /* `r_rows` */
  if (is_analyze)
  {
    ha_rows avg_rows= fake_select_lex_tracker.get_avg_rows();
    item_list.push_back(new Item_int((longlong) (ulonglong) avg_rows,
                                      MY_INT64_NUM_DECIMAL_DIGITS));
  }

  /* `filtered` */
  if (explain_flags & DESCRIBE_EXTENDED || is_analyze)
    item_list.push_back(item_null);

  /* `r_filtered` */
  if (is_analyze)
    item_list.push_back(item_null);

  /* `Extra` */
  StringBuffer<256> extra_buf;
  if (using_filesort)
  {
    extra_buf.append(STRING_WITH_LEN("Using filesort"));
  }
  item_list.push_back(new Item_string_sys(extra_buf.ptr(), extra_buf.length()));

  //output->unit.offset_limit_cnt= 0; 
  if (output->send_data(item_list))
    return 1;
  
  /*
    Print all subquery children (UNION children have already been printed at
    the start of this function)
  */
  return print_explain_for_children(query, output, explain_flags, is_analyze);
}


void Explain_union::print_explain_json(Explain_query *query, 
                                       Json_writer *writer, bool is_analyze)
{
  Json_writer_nesting_guard guard(writer);
  char table_name_buffer[SAFE_NAME_LEN];
  
  writer->add_member("query_block").start_object();
  writer->add_member("union_result").start_object();
  // using_temporary_table
  make_union_table_name(table_name_buffer);
  writer->add_member("table_name").add_str(table_name_buffer);
  writer->add_member("access_type").add_str("ALL"); // not very useful
  writer->add_member("query_specifications").start_array();

  for (int i= 0; i < (int) union_members.elements(); i++)
  {
    writer->start_object();
    //writer->add_member("dependent").add_str("TODO");
    //writer->add_member("cacheable").add_str("TODO");
    Explain_select *sel= query->get_select(union_members.at(i));
    sel->print_explain_json(query, writer, is_analyze);
    writer->end_object();
  }
  writer->end_array();

  print_explain_json_for_children(query, writer, is_analyze);

  writer->end_object(); // union_result
  writer->end_object(); // query_block
}


/*
  Print EXPLAINs for all children nodes (i.e. for subqueries)
*/

int Explain_node::print_explain_for_children(Explain_query *query, 
                                             select_result_sink *output,
                                             uint8 explain_flags, 
                                             bool is_analyze)
{
  for (int i= 0; i < (int) children.elements(); i++)
  {
    Explain_node *node= query->get_node(children.at(i));
    if (node->print_explain(query, output, explain_flags, is_analyze))
      return 1;
  }
  return 0;
}


/*
  This tells whether a child subquery should be printed in JSON output.

  Derived tables and Non-merged semi-joins should not be printed, because they
  are printed inline in Explain_table_access.
*/
bool is_connection_printable_in_json(enum Explain_node::explain_connection_type type)
{
  return (type != Explain_node::EXPLAIN_NODE_DERIVED && 
          type != Explain_node::EXPLAIN_NODE_NON_MERGED_SJ);
}


void Explain_node::print_explain_json_for_children(Explain_query *query, 
                                                  Json_writer *writer,
                                                  bool is_analyze)
{
  Json_writer_nesting_guard guard(writer);
  
  bool started= false;
  for (int i= 0; i < (int) children.elements(); i++)
  {
    Explain_node *node= query->get_node(children.at(i));
    /* Derived tables are printed inside Explain_table_access objects */
    
    if (!is_connection_printable_in_json(node->connection_type))
      continue;

    if (!started)
    {
      writer->add_member("subqueries").start_array();
      started= true;
    }

    writer->start_object();
    node->print_explain_json(query, writer, is_analyze);
    writer->end_object();
  }

  if (started)
    writer->end_array();
}


void Explain_select::replace_table(uint idx, Explain_table_access *new_tab)
{
  delete join_tabs[idx];
  join_tabs[idx]= new_tab;
}


Explain_select::~Explain_select()
{
  if (join_tabs)
  {
    for (uint i= 0; i< n_join_tabs; i++)
      delete join_tabs[i];
    my_free(join_tabs);
  }
} 


int Explain_select::print_explain(Explain_query *query, 
                                  select_result_sink *output,
                                  uint8 explain_flags, bool is_analyze)
{
  if (message)
  {
    List<Item> item_list;
    Item *item_null= new Item_null();

    item_list.push_back(new Item_int((int32) select_id));
    item_list.push_back(new Item_string_sys(select_type));
    for (uint i=0 ; i < 7; i++)
      item_list.push_back(item_null);
    if (explain_flags & DESCRIBE_PARTITIONS)
      item_list.push_back(item_null);

    /* filtered */
    if (is_analyze || explain_flags & DESCRIBE_EXTENDED)
      item_list.push_back(item_null);
    
    if (is_analyze)
    {
      /* r_rows, r_filtered */
      item_list.push_back(item_null);
      item_list.push_back(item_null);
    }

    item_list.push_back(new Item_string_sys(message));

    if (output->send_data(item_list))
      return 1;
  }
  else
  {
    bool using_tmp= using_temporary;
    bool using_fs= using_filesort;
    for (uint i=0; i< n_join_tabs; i++)
    {
      join_tabs[i]->print_explain(output, explain_flags, is_analyze, select_id,
                                  select_type, using_tmp, using_fs);
      if (i == 0)
      {
        /* 
          "Using temporary; Using filesort" should only be shown near the 1st
          table
        */
        using_tmp= false;
        using_fs= false;
      }
    }
  }

  return print_explain_for_children(query, output, explain_flags, is_analyze);
}


void Explain_select::print_explain_json(Explain_query *query, 
                                        Json_writer *writer, bool is_analyze)
{
  Json_writer_nesting_guard guard(writer);

  writer->add_member("query_block").start_object();
  writer->add_member("select_id").add_ll(select_id);
  if (message)
  {
    writer->add_member("table").start_object();
    writer->add_member("message").add_str(message);
    writer->end_object();
  }
  else
  {
    for (uint i=0; i< n_join_tabs; i++)
    {
      // psergey-todo: Need to honor SJM nests...
      join_tabs[i]->print_explain_json(query, writer, is_analyze);
    }
  }

  print_explain_json_for_children(query, writer, is_analyze);
  writer->end_object();
}


void Explain_table_access::push_extra(enum explain_extra_tag extra_tag)
{
  extra_tags.append(extra_tag);
}


/*
  Put the contents of 'key' field of EXPLAIN otuput into key_str.

  It is surprisingly complex:
  - hash join shows #hash#used_key
  - quick selects that use single index will print index name
*/

void Explain_table_access::fill_key_str(String *key_str, bool is_json) const
{
  const CHARSET_INFO *cs= system_charset_info;
  bool is_hj= (type == JT_HASH || type == JT_HASH_NEXT || 
               type == JT_HASH_RANGE || type == JT_HASH_INDEX_MERGE);
  const char *hash_key_prefix= "#hash#";

  if (key.get_key_name())
  {
    if (is_hj)
      key_str->append(hash_key_prefix, strlen(hash_key_prefix), cs);

    key_str->append(key.get_key_name());

    if (is_hj && type != JT_HASH)
      key_str->append(':');
  }
  
  if (quick_info)
  {
    StringBuffer<64> buf2;
    if (is_json)
      quick_info->print_extra_recursive(&buf2);
    else
      quick_info->print_key(&buf2);
    key_str->append(buf2);
  }
  if (type == JT_HASH_NEXT)
    key_str->append(hash_next_key.get_key_name());
}


/*
  Fill "key_length".
   - this is just used key length for ref/range 
   - for index_merge, it is a comma-separated list of lengths.
   - for hash join, it is key_len:pseudo_key_len

  The column looks identical in tabular and json forms. In JSON, we consider
  the column legacy, it is superceded by used_key_parts.
*/

void Explain_table_access::fill_key_len_str(String *key_len_str) const
{
  bool is_hj= (type == JT_HASH || type == JT_HASH_NEXT || 
               type == JT_HASH_RANGE || type == JT_HASH_INDEX_MERGE);
  if (key.get_key_len() != (uint)-1)
  {
    char buf[64];
    size_t length;
    length= longlong10_to_str(key.get_key_len(), buf, 10) - buf;
    key_len_str->append(buf, length);
    if (is_hj && type != JT_HASH)
      key_len_str->append(':');
  }

  if (quick_info)
  {
    StringBuffer<64> buf2;
    quick_info->print_key_len(&buf2);
    key_len_str->append(buf2);
  } 

  if (type == JT_HASH_NEXT)
  {
    char buf[64];
    size_t length;
    length= longlong10_to_str(hash_next_key.get_key_len(), buf, 10) - buf;
    key_len_str->append(buf, length);
  }
}


void Explain_index_use::set(MEM_ROOT *mem_root, KEY *key, uint key_len_arg)
{
  set_pseudo_key(mem_root, key->name);
  key_len= key_len_arg;
  uint len= 0;
  for (uint i= 0; i < key->usable_key_parts; i++)
  {
    key_parts_list.append_str(mem_root, key->key_part[i].field->field_name);
    len += key->key_part[i].store_length;
    if (len >= key_len_arg)
      break;
  }
}


void Explain_index_use::set_pseudo_key(MEM_ROOT *root, const char* key_name_arg)
{
  if (key_name_arg)
  {
    size_t name_len= strlen(key_name_arg);
    if ((key_name= (char*)alloc_root(root, name_len+1)))
      memcpy(key_name, key_name_arg, name_len+1);
  }
  else
    key_name= NULL;
  key_len= -1;
}


double Explain_table_access::get_r_filtered()
{
  //psergey-todo: modify this to produce separate filtered% for both parts of
  //WHERE.
  double r_filtered= tracker.get_filtered_after_where();
  if (bka_type.is_using_jbuf())
    r_filtered *= jbuf_tracker.get_filtered_after_where();
  return r_filtered;
}


int Explain_table_access::print_explain(select_result_sink *output, uint8 explain_flags, 
                                        bool is_analyze,
                                        uint select_id, const char *select_type,
                                        bool using_temporary, bool using_filesort)
{
  //const CHARSET_INFO *cs= system_charset_info;

  List<Item> item_list;
  Item *item_null= new Item_null();
  
  if (sjm_nest_select_id)
    select_id= sjm_nest_select_id;

  /* `id` column */
  item_list.push_back(new Item_int((int32) select_id));

  /* `select_type` column */
  if (sjm_nest_select_id)
    push_str(&item_list, "MATERIALIZED");
  else
    push_str(&item_list, select_type);

  /* `table` column */
  push_string(&item_list, &table_name);
  
  /* `partitions` column */
  if (explain_flags & DESCRIBE_PARTITIONS)
  {
    if (used_partitions_set)
    {
      push_string(&item_list, &used_partitions);
    }
    else
      item_list.push_back(item_null); 
  }

  /* `type` column */
  push_str(&item_list, join_type_str[type]);

  /* `possible_keys` column */
  StringBuffer<64> possible_keys_buf;
  if (possible_keys.is_empty())
    item_list.push_back(item_null); 
  else
    push_string_list(&item_list, possible_keys, &possible_keys_buf);

  /* `key` */
  StringBuffer<64> key_str;
  fill_key_str(&key_str, false);
  
  if (key_str.length() > 0)
    push_string(&item_list, &key_str);
  else
    item_list.push_back(item_null); 

  /* `key_len` */
  StringBuffer<64> key_len_str;
  fill_key_len_str(&key_len_str);

  if (key_len_str.length() > 0)
    push_string(&item_list, &key_len_str);
  else
    item_list.push_back(item_null);

  /* `ref` */
  StringBuffer<64> ref_list_buf;
  if (ref_list.is_empty())
  {
    if (type == JT_FT)
    {
      /* Traditionally, EXPLAIN lines with type=fulltext have ref='' */
      push_str(&item_list, "");
    }
    else
      item_list.push_back(item_null);
  }
  else
    push_string_list(&item_list, ref_list, &ref_list_buf);
 
  /* `rows` */
  if (rows_set)
  {
    item_list.push_back(new Item_int((longlong) (ulonglong) rows, 
                         MY_INT64_NUM_DECIMAL_DIGITS));
  }
  else
    item_list.push_back(item_null);

  /* `r_rows` */
  if (is_analyze)
  {
    if (!tracker.has_scans())
    {
      item_list.push_back(item_null);
    }
    else
    {
      ha_rows avg_rows= tracker.get_avg_rows();
      item_list.push_back(new Item_int((longlong) (ulonglong) avg_rows,
                                        MY_INT64_NUM_DECIMAL_DIGITS));
    }
  }

  /* `filtered` */
  if (explain_flags & DESCRIBE_EXTENDED || is_analyze)
  {
    if (filtered_set)
    {
      item_list.push_back(new Item_float(filtered, 2));
    }
    else
      item_list.push_back(item_null);
  }

  /* `r_filtered` */
  if (is_analyze)
  {
    if (!tracker.has_scans())
    {
      item_list.push_back(item_null);
    }
    else
    {
      double r_filtered= tracker.get_filtered_after_where();
      if (bka_type.is_using_jbuf())
        r_filtered *= jbuf_tracker.get_filtered_after_where();
      item_list.push_back(new Item_float(r_filtered*100.0, 2));
    }
  }

  /* `Extra` */
  StringBuffer<256> extra_buf;
  bool first= true;
  for (int i=0; i < (int)extra_tags.elements(); i++)
  {
    if (first)
      first= false;
    else
      extra_buf.append(STRING_WITH_LEN("; "));
    append_tag_name(&extra_buf, extra_tags.at(i));
  }

  if (using_temporary)
  {
    if (first)
      first= false;
    else
      extra_buf.append(STRING_WITH_LEN("; "));
    extra_buf.append(STRING_WITH_LEN("Using temporary"));
  }

  if (using_filesort)
  {
    if (first)
      first= false;
    else
      extra_buf.append(STRING_WITH_LEN("; "));
    extra_buf.append(STRING_WITH_LEN("Using filesort"));
  }

  item_list.push_back(new Item_string_sys(extra_buf.ptr(), extra_buf.length()));

  if (output->send_data(item_list))
    return 1;

  return 0;
}


bool String_list::append_str(MEM_ROOT *mem_root, const char *str)
{
  size_t len= strlen(str);
  char *cp;
  if (!(cp = (char*)alloc_root(mem_root, len+1)))
    return 1;
  memcpy(cp, str, len+1);
  push_back(cp);
  return 0;
}


static void write_item(Json_writer *writer, Item *item)
{
  THD *thd= current_thd;
  char item_buf[256];
  String str(item_buf, sizeof(item_buf), &my_charset_bin);
  str.length(0);

  ulonglong save_option_bits= thd->variables.option_bits;
  thd->variables.option_bits &= ~OPTION_QUOTE_SHOW_CREATE;

  item->print(&str, QT_EXPLAIN);

  thd->variables.option_bits= save_option_bits;
  writer->add_str(str.c_ptr_safe());
}


void Explain_table_access::tag_to_json(Json_writer *writer, enum explain_extra_tag tag)
{
  switch (tag)
  {
    case ET_OPEN_FULL_TABLE:
      writer->add_member("open_full_table").add_bool(true);
      break;
    case ET_SCANNED_0_DATABASES:
      writer->add_member("scanned_databases").add_ll(0);
      break;
    case ET_SCANNED_1_DATABASE:
      writer->add_member("scanned_databases").add_ll(1);
      break;
    case ET_SCANNED_ALL_DATABASES:
      writer->add_member("scanned_databases").add_str("all");
      break;
    case ET_SKIP_OPEN_TABLE:
      writer->add_member("skip_open_table").add_bool(true);
      break;
    case ET_OPEN_FRM_ONLY:
      writer->add_member("open_frm_only").add_bool(true);
      break;
    case ET_USING_INDEX_CONDITION:
      writer->add_member("index_condition");
      write_item(writer, pushed_index_cond);
      break;
    case ET_USING_WHERE:
      if (where_cond)
      {
        writer->add_member("attached_condition");
        /*
          We are printing the condition that is checked when scanning this
          table.
          - when join buffer is used, it is cache_cond. 
          - in other cases, it is where_cond.
        */
        Item *item= bka_type.is_using_jbuf()? cache_cond: where_cond;
        write_item(writer, item);
      }
      break;
    case ET_USING_INDEX:
      writer->add_member("using_index").add_bool(true);
      break;
    case ET_USING:
      // index merge: case ET_USING 
      break;
    case ET_USING_JOIN_BUFFER:
      /* Do nothing. Join buffer is handled differently */
      break;
    default:
      DBUG_ASSERT(0);
  }
}


void Explain_table_access::print_explain_json(Explain_query *query,
                                              Json_writer *writer,
                                              bool is_analyze)
{
  Json_writer_nesting_guard guard(writer);

  if (bka_type.is_using_jbuf())
  {
    writer->add_member("block-nl-join").start_object();
  }

  writer->add_member("table").start_object();

  writer->add_member("table_name").add_str(table_name);
  // partitions
  writer->add_member("access_type").add_str(join_type_str[type]);
  if (!possible_keys.is_empty())
  {
    List_iterator_fast<char> it(possible_keys);
    const char *name;
    writer->add_member("possible_keys").start_array();
    while ((name= it++))
      writer->add_str(name);
    writer->end_array();
  }

  /* `key` */
  /* For non-basic quick select, 'key' will not be present */
  if (!quick_info || quick_info->is_basic())
  {
    StringBuffer<64> key_str;
    fill_key_str(&key_str, true);
    if (key_str.length())
      writer->add_member("key").add_str(key_str);
  }

  /* `key_length` */
  StringBuffer<64> key_len_str;
  fill_key_len_str(&key_len_str);
  if (key_len_str.length())
    writer->add_member("key_length").add_str(key_len_str);

  /* `used_key_parts` */
  String_list *parts_list= NULL;
  if (quick_info && quick_info->is_basic())
    parts_list= &quick_info->range.key_parts_list;
  else
    parts_list= &key.key_parts_list;

  if (parts_list && !parts_list->is_empty())
  {
    List_iterator_fast<char> it(*parts_list);
    const char *name;
    writer->add_member("used_key_parts").start_array();
    while ((name= it++))
      writer->add_str(name);
    writer->end_array();
  }

  if (quick_info && !quick_info->is_basic())
  {
    writer->add_member("index_merge").start_object();
    quick_info->print_json(writer);
    writer->end_object();
  }
  
  /* `ref` */
  if (!ref_list.is_empty())
  {
    List_iterator_fast<char> it(ref_list);
    const char *str;
    writer->add_member("ref").start_array();
    while ((str= it++))
      writer->add_str(str);
    writer->end_array();
  }

  /* `rows` */
  if (rows_set)
    writer->add_member("rows").add_ll(rows);

  /* `r_rows` */
  if (is_analyze && tracker.has_scans())
  {
    ha_rows avg_rows= tracker.get_avg_rows();
    writer->add_member("r_rows").add_ll(avg_rows);
  }
  
  /* `filtered` */
  if (filtered_set)
    writer->add_member("filtered").add_double(filtered);

  /* `r_filtered` */
  if (is_analyze)
    writer->add_member("r_filtered").add_double(get_r_filtered());

  for (int i=0; i < (int)extra_tags.elements(); i++)
  {
    tag_to_json(writer, extra_tags.at(i));
  }

  if (bka_type.is_using_jbuf())
  {
    writer->end_object();
    writer->add_member("buffer_type").add_str(bka_type.incremental?
                                              "incremental":"flat");
    writer->add_member("join_type").add_str(bka_type.join_alg);
    if (bka_type.mrr_type.length())
      writer->add_member("mrr_type").add_str(bka_type.mrr_type);
    if (where_cond)
    {
      writer->add_member("attached_condition");
      write_item(writer, where_cond);
    }
  }

  if (derived_select_number)
  {
    /* This is a derived table. Print its contents here */
    writer->add_member("materialized").start_object();
    Explain_node *node= query->get_node(derived_select_number);
    node->print_explain_json(query, writer, is_analyze);
    writer->end_object();
  }
  if (non_merged_sjm_number)
  {
    /* This is a non-merged semi-join table. Print its contents here */
    writer->add_member("materialized").start_object();
    writer->add_member("unique").add_ll(1);
    Explain_node *node= query->get_node(non_merged_sjm_number);
    node->connection_type= Explain_node::EXPLAIN_NODE_NON_MERGED_SJ;
    node->print_explain_json(query, writer, is_analyze);
    writer->end_object();
  }

  writer->end_object();
}


/*
  Elements in this array match members of enum Extra_tag, defined in
  sql_explain.h
*/

const char * extra_tag_text[]=
{
  "ET_none",
  "Using index condition",
  "Using index condition(BKA)",
  "Using ", // special handling
  "Range checked for each record (index map: 0x", // special handling
  "Using where with pushed condition",
  "Using where",
  "Not exists",
  
  "Using index",
  "Full scan on NULL key",
  "Skip_open_table",
  "Open_frm_only",
  "Open_full_table", 

  "Scanned 0 databases",
  "Scanned 1 database",
  "Scanned all databases",

  "Using index for group-by", // special handling

  "USING MRR: DONT PRINT ME", // special handling

  "Distinct",
  "LooseScan",
  "Start temporary",
  "End temporary",
  "FirstMatch", // special handling

  "Using join buffer", // special handling 

  "const row not found",
  "unique row not found",
  "Impossible ON condition"
};


void Explain_table_access::append_tag_name(String *str, enum explain_extra_tag tag)
{
  switch (tag) {
    case ET_USING:
    {
      // quick select
      str->append(STRING_WITH_LEN("Using "));
      quick_info->print_extra(str);
      break;
    }
    case ET_RANGE_CHECKED_FOR_EACH_RECORD:
    {
      /* 4 bits per 1 hex digit + terminating '\0' */
      char buf[MAX_KEY / 4 + 1];
      str->append(STRING_WITH_LEN("Range checked for each "
                                   "record (index map: 0x"));
      str->append(range_checked_map.print(buf));
      str->append(')');
      break;
    }
    case ET_USING_MRR:
    {
      str->append(mrr_type);
      break;
    }
    case ET_USING_JOIN_BUFFER:
    {
      str->append(extra_tag_text[tag]);

      str->append(STRING_WITH_LEN(" ("));
      const char *buffer_type= bka_type.incremental ? "incremental" : "flat";
      str->append(buffer_type);
      str->append(STRING_WITH_LEN(", "));
      str->append(bka_type.join_alg);
      str->append(STRING_WITH_LEN(" join"));
      str->append(STRING_WITH_LEN(")"));
      if (bka_type.mrr_type.length())
        str->append(bka_type.mrr_type);

      break;
    }
    case ET_FIRST_MATCH:
    {
      if (firstmatch_table_name.length())
      {
        str->append("FirstMatch(");
        str->append(firstmatch_table_name);
        str->append(")");
      }
      else
        str->append(extra_tag_text[tag]);
      break;
    }
    case ET_USING_INDEX_FOR_GROUP_BY:
    {
      str->append(extra_tag_text[tag]);
      if (loose_scan_is_scanning)
        str->append(" (scanning)");
      break;
    }
    default:
     str->append(extra_tag_text[tag]);
  }
}


/* 
  This is called for top-level Explain_quick_select only. The point of this
  function is:
  - index_merge should print $index_merge_type (child, ...)
  - 'range'  should not print anything.
*/

void Explain_quick_select::print_extra(String *str)
{
  if (quick_type == QUICK_SELECT_I::QS_TYPE_RANGE || 
      quick_type == QUICK_SELECT_I::QS_TYPE_RANGE_DESC ||
      quick_type == QUICK_SELECT_I::QS_TYPE_GROUP_MIN_MAX)
  {
    /* print nothing */
  }
  else
    print_extra_recursive(str);
}

void Explain_quick_select::print_json(Json_writer *writer)
{
  if (is_basic())
  {
    writer->add_member("range").start_object();

    writer->add_member("key").add_str(range.get_key_name());
    
    List_iterator_fast<char> it(range.key_parts_list);
    const char *name;
    writer->add_member("used_key_parts").start_array();
    while ((name= it++))
        writer->add_str(name);
    writer->end_array();

    writer->end_object();
  }
  else
  {
    writer->add_member(get_name_by_type()).start_object();

    List_iterator_fast<Explain_quick_select> it (children);
    Explain_quick_select* child;
    while ((child = it++))
      child->print_json(writer);

    writer->end_object();
  }
}

void Explain_quick_select::print_extra_recursive(String *str)
{
  if (quick_type == QUICK_SELECT_I::QS_TYPE_RANGE || 
      quick_type == QUICK_SELECT_I::QS_TYPE_RANGE_DESC)
  {
    str->append(range.get_key_name());
  }
  else
  {
    str->append(get_name_by_type());
    str->append('(');
    List_iterator_fast<Explain_quick_select> it (children);
    Explain_quick_select* child;
    bool first= true;
    while ((child = it++))
    {
      if (first)
        first= false;
      else
        str->append(',');

      child->print_extra_recursive(str);
    }
    str->append(')');
  }
}


const char * Explain_quick_select::get_name_by_type()
{
  switch (quick_type) {
    case QUICK_SELECT_I::QS_TYPE_INDEX_MERGE:
      return "sort_union";
    case QUICK_SELECT_I::QS_TYPE_ROR_UNION:
      return "union";
    case QUICK_SELECT_I::QS_TYPE_ROR_INTERSECT:
      return "intersect";
    case QUICK_SELECT_I::QS_TYPE_INDEX_INTERSECT:
      return "sort_intersect";
    default:
      DBUG_ASSERT(0);
      return "unknown quick select type";
  }
}


/*
  This prints a comma-separated list of used indexes, ignoring nesting
*/

void Explain_quick_select::print_key(String *str)
{
  if (quick_type == QUICK_SELECT_I::QS_TYPE_RANGE || 
      quick_type == QUICK_SELECT_I::QS_TYPE_RANGE_DESC || 
      quick_type == QUICK_SELECT_I::QS_TYPE_GROUP_MIN_MAX)
  {
    if (str->length() > 0)
      str->append(',');
    str->append(range.get_key_name());
  }
  else
  {
    List_iterator_fast<Explain_quick_select> it (children);
    Explain_quick_select* child;
    while ((child = it++))
    {
      child->print_key(str);
    }
  }
}


/*
  This prints a comma-separated list of used key_lengths, ignoring nesting
*/

void Explain_quick_select::print_key_len(String *str)
{
  if (quick_type == QUICK_SELECT_I::QS_TYPE_RANGE || 
      quick_type == QUICK_SELECT_I::QS_TYPE_RANGE_DESC ||
      quick_type == QUICK_SELECT_I::QS_TYPE_GROUP_MIN_MAX)
  {
    char buf[64];
    size_t length;
    length= longlong10_to_str(range.get_key_len(), buf, 10) - buf;
    if (str->length() > 0)
      str->append(',');
    str->append(buf, length);
  }
  else
  {
    List_iterator_fast<Explain_quick_select> it (children);
    Explain_quick_select* child;
    while ((child = it++))
    {
      child->print_key_len(str);
    }
  }
}


int Explain_delete::print_explain(Explain_query *query, 
                                  select_result_sink *output,
                                  uint8 explain_flags,
                                  bool is_analyze)
{
  if (deleting_all_rows)
  {
    const char *msg= STR_DELETING_ALL_ROWS;
    int res= print_explain_message_line(output, explain_flags, is_analyze,
                                        1 /*select number*/,
                                        select_type, &rows, msg);
    return res;

  }
  else
  {
    return Explain_update::print_explain(query, output, explain_flags,
                                         is_analyze);
  }
}


void Explain_delete::print_explain_json(Explain_query *query, 
                                        Json_writer *writer,
                                        bool is_analyze)
{
  Json_writer_nesting_guard guard(writer);

  if (deleting_all_rows)
  {
    writer->add_member("query_block").start_object();
    writer->add_member("select_id").add_ll(1);
    writer->add_member("table").start_object();
    // just like mysql-5.6, we don't print table name. Is this ok?
    writer->add_member("message").add_str(STR_DELETING_ALL_ROWS);
    writer->end_object(); // table
    writer->end_object(); // query_block
    return;
  }
  Explain_update::print_explain_json(query, writer, is_analyze);
}


int Explain_update::print_explain(Explain_query *query, 
                                  select_result_sink *output,
                                  uint8 explain_flags,
                                  bool is_analyze)
{
  StringBuffer<64> key_buf;
  StringBuffer<64> key_len_buf;
  StringBuffer<64> extra_str;
  if (impossible_where || no_partitions)
  {
    const char *msg= impossible_where ? 
                     STR_IMPOSSIBLE_WHERE : 
                     STR_NO_ROWS_AFTER_PRUNING;
    int res= print_explain_message_line(output, explain_flags, is_analyze,
                                        1 /*select number*/,
                                        select_type, 
                                        NULL, /* rows */
                                        msg);
    return res;
  }

  if (quick_info)
  {
    quick_info->print_key(&key_buf);
    quick_info->print_key_len(&key_len_buf);

    StringBuffer<64> quick_buf;
    quick_info->print_extra(&quick_buf);
    if (quick_buf.length())
    {
      extra_str.append(STRING_WITH_LEN("Using "));
      extra_str.append(quick_buf);
    }
  }
  else if (key.get_key_name())
  {
    const char *name= key.get_key_name();
    key_buf.set(name, strlen(name), &my_charset_bin);
    char buf[64];
    size_t length= longlong10_to_str(key.get_key_len(), buf, 10) - buf;
    key_len_buf.copy(buf, length, &my_charset_bin);
  }

  if (using_where)
  {
    if (extra_str.length() !=0)
      extra_str.append(STRING_WITH_LEN("; "));
    extra_str.append(STRING_WITH_LEN("Using where"));
  }

  if (mrr_type.length() != 0)
  {
    if (extra_str.length() !=0)
      extra_str.append(STRING_WITH_LEN("; "));
    extra_str.append(mrr_type);
  }
  
  if (using_filesort)
  {
    if (extra_str.length() !=0)
      extra_str.append(STRING_WITH_LEN("; "));
    extra_str.append(STRING_WITH_LEN("Using filesort"));
  }

  if (using_io_buffer)
  {
    if (extra_str.length() !=0)
      extra_str.append(STRING_WITH_LEN("; "));
    extra_str.append(STRING_WITH_LEN("Using buffer"));
  }

  /* 
    Single-table DELETE commands do not do "Using temporary".
    "Using index condition" is also not possible (which is an unjustified limitation)
  */
  double r_filtered= 100 * tracker.get_filtered_after_where();
  ha_rows r_rows= tracker.get_avg_rows();

  print_explain_row(output, explain_flags, is_analyze,
                    1, /* id */
                    select_type,
                    table_name.c_ptr(), 
                    used_partitions_set? used_partitions.c_ptr() : NULL,
                    jtype,
                    &possible_keys,
                    key_buf.length()? key_buf.c_ptr() : NULL,
                    key_len_buf.length() ? key_len_buf.c_ptr() : NULL,
                    NULL, /* 'ref' is always NULL in single-table EXPLAIN DELETE */
                    &rows,
                    tracker.has_scans()? &r_rows : NULL,
                    r_filtered,
                    extra_str.c_ptr_safe());

  return print_explain_for_children(query, output, explain_flags, is_analyze);
}


void Explain_update::print_explain_json(Explain_query *query,
                                        Json_writer *writer,
                                        bool is_analyze)
{
  Json_writer_nesting_guard guard(writer);

  writer->add_member("query_block").start_object();
  writer->add_member("select_id").add_ll(1);

  if (impossible_where || no_partitions)
  {
    const char *msg= impossible_where ?  STR_IMPOSSIBLE_WHERE : 
                                         STR_NO_ROWS_AFTER_PRUNING;
    writer->add_member("table").start_object();
    writer->add_member("message").add_str(msg);
    writer->end_object(); // table
    writer->end_object(); // query_block
    return;
  }

  writer->add_member("table").start_object();

  if (get_type() == EXPLAIN_UPDATE)
    writer->add_member("update").add_ll(1);
  else
    writer->add_member("delete").add_ll(1);

  writer->add_member("table_name").add_str(table_name);
  writer->add_member("access_type").add_str(join_type_str[jtype]);

  if (!possible_keys.is_empty())
  {
    List_iterator_fast<char> it(possible_keys);
    const char *name;
    writer->add_member("possible_keys").start_array();
    while ((name= it++))
      writer->add_str(name);
    writer->end_array();
  }

  /* `key`, `key_length` */
  if (quick_info && quick_info->is_basic())
  {
    StringBuffer<64> key_buf;
    StringBuffer<64> key_len_buf;
    quick_info->print_extra_recursive(&key_buf);
    quick_info->print_key_len(&key_len_buf);
    
    writer->add_member("key").add_str(key_buf);
    writer->add_member("key_length").add_str(key_len_buf);
  }
  else if (key.get_key_name())
  {
    writer->add_member("key").add_str(key.get_key_name());
    writer->add_member("key_length").add_str(key.get_key_len());
  }

  /* `used_key_parts` */
  String_list *parts_list= NULL;
  if (quick_info && quick_info->is_basic())
    parts_list= &quick_info->range.key_parts_list;
  else
    parts_list= &key.key_parts_list;

  if (parts_list && !parts_list->is_empty())
  {
    List_iterator_fast<char> it(*parts_list);
    const char *name;
    writer->add_member("used_key_parts").start_array();
    while ((name= it++))
      writer->add_str(name);
    writer->end_array();
  }

  if (quick_info && !quick_info->is_basic())
  {
    writer->add_member("index_merge").start_object();
    quick_info->print_json(writer);
    writer->end_object();
  }
  
#if 0
  /* `ref` */
  if (!ref_list.is_empty())
  {
    List_iterator_fast<char> it(ref_list);
    const char *str;
    writer->add_member("ref").start_array();
    while ((str= it++))
      writer->add_str(str);
    writer->end_array();
  }
#endif

  /* `rows` */
  writer->add_member("rows").add_ll(rows);

  /* `r_rows` */
  if (is_analyze && tracker.has_scans())
  {
    ha_rows avg_rows= tracker.get_avg_rows();
    writer->add_member("r_rows").add_ll(avg_rows);
  }
 
  /* UPDATE/DELETE do not produce `filtered` estimate */

  /* `r_filtered` */
  if (is_analyze)
  {
    double r_filtered= tracker.get_filtered_after_where();
    writer->add_member("r_filtered").add_double(r_filtered);
  }

  if (mrr_type.length() != 0)
    writer->add_member("mrr_type").add_str(mrr_type.ptr());
  
  if (using_filesort)
    writer->add_member("using_filesort").add_ll(1);

  if (using_io_buffer)
    writer->add_member("using_io_buffer").add_ll(1);

  if (where_cond)
  {
    writer->add_member("attached_condition");
    write_item(writer, where_cond);
  }

  writer->end_object(); // table
  print_explain_json_for_children(query, writer, is_analyze);
  writer->end_object(); // query_block
}


int Explain_insert::print_explain(Explain_query *query, 
                                  select_result_sink *output, 
                                  uint8 explain_flags,
                                  bool is_analyze)
{
  const char *select_type="INSERT";
  print_explain_row(output, explain_flags, is_analyze,
                    1, /* id */
                    select_type,
                    table_name.c_ptr(), 
                    NULL, // partitions
                    JT_ALL,
                    NULL, // possible_keys
                    NULL, // key
                    NULL, // key_len
                    NULL, // ref
                    NULL, // rows
                    NULL, // r_rows
                    100.0, // r_filtered
                    NULL);

  return print_explain_for_children(query, output, explain_flags, is_analyze);
}


void delete_explain_query(LEX *lex)
{
  DBUG_ENTER("delete_explain_query");
  delete lex->explain;
  lex->explain= NULL;
  DBUG_VOID_RETURN;
}


void create_explain_query(LEX *lex, MEM_ROOT *mem_root)
{
  DBUG_ASSERT(!lex->explain);
  lex->explain= new Explain_query(lex->thd);
  DBUG_ASSERT(mem_root == current_thd->mem_root);
  lex->explain->mem_root= mem_root;
}

void create_explain_query_if_not_exists(LEX *lex, MEM_ROOT *mem_root)
{
  if (!lex->explain)
    create_explain_query(lex, mem_root);
}