MDEV-3798: EXPLAIN UPDATE/DELETE

- Generate correct contents of `Extra` column for UPDATEs/DELETEs that use quick selects
- UPDATEs with used_key_is_modified=true will show "Using buffer"

sql/sql_delete.cc

@@ -142,14 +142,16 @@ void Update_plan::save_explain_data_intern(Explain_query *query,
 
   explain->using_where= test(select && select->cond);
   explain->using_filesort= using_filesort;
+  explain->using_io_buffer= using_io_buffer;
 
   make_possible_keys_line(table, possible_keys, &explain->possible_keys_line);
 
+  explain->quick_info= NULL;
+
   /* Calculate key_len */
   if (select && select->quick)
   {
-    select->quick->add_keys_and_lengths(&explain->key_str, 
-                                        &explain->key_len_str);
+    explain->quick_info= select->quick->get_explain(mem_root);
   }
   else
   {
@@ -218,7 +220,7 @@ bool mysql_delete(THD *thd, TABLE_LIST *table_list, COND *conds,
   killed_state killed_status= NOT_KILLED;
   THD::enum_binlog_query_type query_type= THD::ROW_QUERY_TYPE;
   bool with_select= !select_lex->item_list.is_empty();
-  Delete_plan query_plan;
+  Delete_plan query_plan(thd->mem_root);
   query_plan.index= MAX_KEY;
   query_plan.using_filesort= FALSE;
   DBUG_ENTER("mysql_delete");

sql/sql_explain.cc

@@ -793,6 +793,8 @@ int Explain_update::print_explain(Explain_query *query,
                                   select_result_sink *output,
                                   uint8 explain_flags)
 {
+  StringBuffer<64> key_buf;
+  StringBuffer<64> key_len_buf;
   StringBuffer<64> extra_str;
   if (impossible_where || no_partitions)
   {
@@ -807,8 +809,32 @@ int Explain_update::print_explain(Explain_query *query,
     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
+  {
+    key_buf.copy(key_str);
+    key_len_buf.copy(key_len_str);
+  }
+
   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)
   {
@@ -816,7 +842,7 @@ int Explain_update::print_explain(Explain_query *query,
       extra_str.append(STRING_WITH_LEN("; "));
     extra_str.append(mrr_type);
   }
-
+  
   if (using_filesort)
   {
     if (extra_str.length() !=0)
@@ -824,6 +850,13 @@ int Explain_update::print_explain(Explain_query *query,
     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)
@@ -836,8 +869,8 @@ int Explain_update::print_explain(Explain_query *query,
                     used_partitions_set? used_partitions.c_ptr() : NULL,
                     jtype,
                     possible_keys_line.length()? possible_keys_line.c_ptr(): NULL,
-                    key_str.length()? key_str.c_ptr() : NULL,
-                    key_len_str.length() ? key_len_str.c_ptr() : NULL,
+                    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,
                     extra_str.c_ptr());
@@ -846,7 +879,8 @@ int Explain_update::print_explain(Explain_query *query,
 }
 
 
-int Explain_insert::print_explain(Explain_query *query, select_result_sink *output, 
+int Explain_insert::print_explain(Explain_query *query, 
+                                  select_result_sink *output, 
                                   uint8 explain_flags)
 {
   const char *select_type="INSERT";

sql/sql_explain.h

@@ -486,10 +486,13 @@ public:
   StringBuffer<128> key_len_str;
   StringBuffer<64> mrr_type;
   
+  Explain_quick_select *quick_info;
+
   bool using_where;
   ha_rows rows;
 
   bool using_filesort;
+  bool using_io_buffer;
 
   virtual int print_explain(Explain_query *query, select_result_sink *output, 
                             uint8 explain_flags);

sql/sql_lex.h

@@ -2390,6 +2390,9 @@ public:
     select should not be shown when printing EXPLAIN.
   */
   bool updating_a_view;
+   
+  /* Allocate things there */
+  MEM_ROOT *mem_root;
 
   TABLE *table;
   SQL_SELECT *select;
@@ -2403,6 +2406,7 @@ public:
   
   key_map possible_keys;
   bool using_filesort;
+  bool using_io_buffer;
   
   /* Set this plan to be a plan to do nothing because of impossible WHERE */
   void set_impossible_where() { impossible_where= true; }
@@ -2412,8 +2416,10 @@ public:
   void save_explain_data_intern(Explain_query *query, Explain_update *eu);
   virtual ~Update_plan() {}
 
-  Update_plan() : 
-    impossible_where(false), no_partitions(false), using_filesort(false) 
+  Update_plan(MEM_ROOT *mem_root_arg) : 
+    impossible_where(false), no_partitions(false), 
+    mem_root(mem_root_arg), 
+    using_filesort(false), using_io_buffer(false)
   {}
 };
 
@@ -2425,8 +2431,10 @@ class Delete_plan : public Update_plan
 public:
 
   /* Construction functions */
-  Delete_plan() : 
-    deleting_all_rows(false)  {}
+  Delete_plan(MEM_ROOT *mem_root_arg) : 
+    Update_plan(mem_root_arg), 
+    deleting_all_rows(false)
+  {}
 
   /* Set this query plan to be a plan to make a call to h->delete_all_rows() */
   void set_delete_all_rows(ha_rows rows_arg) 

sql/sql_update.cc

@@ -276,7 +276,7 @@ int mysql_update(THD *thd,
   ulonglong     id;
   List<Item> all_fields;
   killed_state killed_status= NOT_KILLED;
-  Update_plan query_plan;
+  Update_plan query_plan(thd->mem_root);
   query_plan.index= MAX_KEY;
   query_plan.using_filesort= FALSE;
   bool apc_target_enabled= false; // means was enabled *by code this function*
@@ -495,6 +495,17 @@ int mysql_update(THD *thd,
   query_plan.table_rows= table->file->stats.records;
   query_plan.possible_keys= select? select->possible_keys: key_map(0);
   
+  if (used_key_is_modified || order ||
+      partition_key_modified(table, table->write_set))
+  {
+    if (order && (need_sort || used_key_is_modified))
+      query_plan.using_filesort= true;
+    else
+      query_plan.using_io_buffer= true;
+  }
+
+  query_plan.save_explain_data(thd->lex->explain);
+
   /*
     Ok, we have generated a query plan for the UPDATE.
      - if we're running EXPLAIN UPDATE, goto produce explain output 
@@ -502,16 +513,12 @@ int mysql_update(THD *thd,
   */
   if (thd->lex->describe)
     goto exit_without_my_ok;
-
-  query_plan.save_explain_data(thd->lex->explain);
   thd->apc_target.enable();
   apc_target_enabled= true;
   DBUG_EXECUTE_IF("show_explain_probe_update_exec_start", 
                   dbug_serve_apcs(thd, 1););
-
-
-  if (used_key_is_modified || order ||
-      partition_key_modified(table, table->write_set))
+  
+  if (query_plan.using_filesort || query_plan.using_io_buffer)
   {
     /*
       We can't update table directly;  We must first search after all
@@ -528,7 +535,7 @@ int mysql_update(THD *thd,
       table->use_all_columns();
 
     /* note: We avoid sorting if we sort on the used index */
-    if (order && (need_sort || used_key_is_modified))
+    if (query_plan.using_filesort)
     {
       /*
 	Doing an ORDER BY;  Let filesort find and sort the rows we are going
@@ -1034,7 +1041,6 @@ err:
 
 exit_without_my_ok:
   DBUG_ASSERT(!apc_target_enabled);
-  query_plan.save_explain_data(thd->lex->explain);
 
   int err2= thd->lex->explain->send_explain(thd);