MDEV-21201 No records produced in information_schema query, depending on projection

Reimplement MDEV-14275 Improving memory utilization for information schema

Postpone temp table instantiation until after setup_fields().

Replace all unused (not marked in read_set) columns in an I_S table
with CHAR(0). This can drastically reduce the footprint of a MEMORY
table (a TABLE_CATALOG alone is 1538 bytes per row).

This does not change the engine. If the table was decided to be Aria
(because of, say, blobs) then after optimization it'll stay Aria
even if all blobs were removed.

Note 1: when transforming table structure, share->blob_fields is
preserved, otherwise Aria might switch from DYNAMIC to STATIC row format
and expect a special field for a deleted mark, which create_tmp_tabe
didn't provide.

Note 2: optimizer was doing handler::info() (to know the number of rows)
before the temp table is populated. That didn't make much sense. Now
it's done before the table is even instantiated. Preserve the old
behavior and report 0 rows.

This reverts e2664ee8362 and a8458a2345e

1 files changed, 78 insertions, 102 deletions

diff --git a/sql/sql_show.cc b/sql/sql_show.cc
index 2a569204908..6bd8c9b5c27 100644
--- a/sql/sql_show.cc
+++ b/sql/sql_show.cc
@@ -3700,8 +3700,6 @@ static bool show_status_array(THD *thd, const char *wild,
   CHARSET_INFO *charset= system_charset_info;
   DBUG_ENTER("show_status_array");
 
-  thd->count_cuted_fields= CHECK_FIELD_WARN;
-
   prefix_end=strnmov(name_buffer, prefix, sizeof(name_buffer)-1);
   if (*prefix)
     *prefix_end++= '_';
@@ -3801,6 +3799,8 @@ static bool show_status_array(THD *thd, const char *wild,
         pos= get_one_variable(thd, var, scope, show_type, status_var,
                               &charset, buff, &length);
 
+        if (table->field[1]->field_length)
+          thd->count_cuted_fields= CHECK_FIELD_WARN;
         table->field[1]->store(pos, (uint32) length, charset);
         thd->count_cuted_fields= CHECK_FIELD_IGNORE;
         table->field[1]->set_notnull();
@@ -8108,51 +8108,6 @@ ST_SCHEMA_TABLE *get_schema_table(enum enum_schema_tables schema_table_idx)
   return &schema_tables[schema_table_idx];
 }
 
-static void
-mark_all_fields_used_in_query(THD *thd,
-                              ST_FIELD_INFO *schema_fields,
-                              MY_BITMAP *bitmap,
-                              Item *all_items)
-{
-  Item *item;
-  DBUG_ENTER("mark_all_fields_used_in_query");
-
-  /* If not SELECT command, return all columns */
-  if (thd->lex->sql_command != SQLCOM_SELECT &&
-      thd->lex->sql_command != SQLCOM_SET_OPTION)
-  {
-    bitmap_set_all(bitmap);
-    DBUG_VOID_RETURN;
-  }
-
-  for (item= all_items ; item ; item= item->next)
-  {
-    if (item->type() == Item::FIELD_ITEM)
-    {
-      ST_FIELD_INFO *fields= schema_fields;
-      uint count;
-      Item_field *item_field= (Item_field*) item;
-
-      /* item_field can be '*' as this function is called before fix_fields */
-      if (item_field->field_name.str == star_clex_str.str)
-      {
-        bitmap_set_all(bitmap);
-        break;
-      }
-      for (count=0; fields->field_name; fields++, count++)
-      {
-        if (!my_strcasecmp(system_charset_info, fields->field_name,
-                           item_field->field_name.str))
-        {
-          bitmap_set_bit(bitmap, count);
-          break;
-        }
-      }
-    }
-  }
-  DBUG_VOID_RETURN;
-}
-
 /**
   Create information_schema table using schema_table data.
 
@@ -8176,37 +8131,19 @@ mark_all_fields_used_in_query(THD *thd,
 
 TABLE *create_schema_table(THD *thd, TABLE_LIST *table_list)
 {
-  uint field_count;
-  Item *item, *all_items;
+  uint field_count= 0;
+  Item *item;
   TABLE *table;
   List<Item> field_list;
   ST_SCHEMA_TABLE *schema_table= table_list->schema_table;
   ST_FIELD_INFO *fields_info= schema_table->fields_info;
-  ST_FIELD_INFO *fields;
   CHARSET_INFO *cs= system_charset_info;
   MEM_ROOT *mem_root= thd->mem_root;
-  MY_BITMAP bitmap;
-  my_bitmap_map *buf;
+  bool need_all_fieds= table_list->schema_table_reformed || // SHOW command
+                       thd->lex->only_view_structure(); // need table structure
   DBUG_ENTER("create_schema_table");
 
-  for (field_count= 0, fields= fields_info; fields->field_name; fields++)
-    field_count++;
-  if (!(buf= (my_bitmap_map*) thd->alloc(bitmap_buffer_size(field_count))))
-    DBUG_RETURN(NULL);
-  my_bitmap_init(&bitmap, buf, field_count, 0);
-
-  if (!thd->stmt_arena->is_conventional() &&
-      thd->mem_root != thd->stmt_arena->mem_root)
-    all_items= thd->stmt_arena->free_list;
-  else
-    all_items= thd->free_list;
-
-  if (table_list->part_of_natural_join)
-    bitmap_set_all(&bitmap);
-  else
-    mark_all_fields_used_in_query(thd, fields_info, &bitmap, all_items);
-
-  for (field_count=0; fields_info->field_name; fields_info++)
+  for (; fields_info->field_name; fields_info++)
   {
     size_t field_name_length= strlen(fields_info->field_name);
     switch (fields_info->field_type) {
@@ -8283,44 +8220,19 @@ TABLE *create_schema_table(THD *thd, TABLE_LIST *table_list)
     case MYSQL_TYPE_MEDIUM_BLOB:
     case MYSQL_TYPE_LONG_BLOB:
     case MYSQL_TYPE_BLOB:
-      if (bitmap_is_set(&bitmap, field_count))
-      {
-        if (!(item= new (mem_root)
-              Item_blob(thd, fields_info->field_name,
-                        fields_info->field_length)))
-        {
-          DBUG_RETURN(0);
-        }
-      }
-      else
-      {
-        if (!(item= new (mem_root)
-              Item_empty_string(thd, "", 0, cs)))
-        {
-          DBUG_RETURN(0);
-        }
-        item->set_name(thd, fields_info->field_name,
-                       field_name_length, cs);
-      }
+      if (!(item= new (mem_root) Item_blob(thd, fields_info->field_name,
+                                           fields_info->field_length)))
+        DBUG_RETURN(0);
       break;
     default:
-    {
-      bool show_field;
       /* Don't let unimplemented types pass through. Could be a grave error. */
       DBUG_ASSERT(fields_info->field_type == MYSQL_TYPE_STRING);
-
-      show_field= bitmap_is_set(&bitmap, field_count);
-      if (!(item= new (mem_root)
-            Item_empty_string(thd, "",
-                              show_field ? fields_info->field_length : 0, cs)))
-      {
+      if (!(item= new (mem_root) Item_empty_string(thd, "",
+                                               fields_info->field_length, cs)))
         DBUG_RETURN(0);
-      }
-      item->set_name(thd, fields_info->field_name,
-                     field_name_length, cs);
+      item->set_name(thd, fields_info->field_name, field_name_length, cs);
       break;
     }
-    }
     field_list.push_back(item, thd->mem_root);
     item->maybe_null= (fields_info->field_flags & MY_I_S_MAYBE_NULL);
     field_count++;
@@ -8335,7 +8247,7 @@ TABLE *create_schema_table(THD *thd, TABLE_LIST *table_list)
   if (!(table= create_tmp_table(thd, tmp_table_param, field_list, (ORDER*) 0, 0,
                  0, (select_lex->options | thd->variables.option_bits |
                  TMP_TABLE_ALL_COLUMNS), HA_POS_ERROR,
-                 &table_list->alias, false, keep_row_order)))
+                 &table_list->alias, !need_all_fieds, keep_row_order)))
     DBUG_RETURN(0);
   my_bitmap_map* bitmaps=
     (my_bitmap_map*) thd->alloc(bitmap_buffer_size(field_count));
@@ -8751,6 +8663,67 @@ end:
 }
 
 
+static int optimize_schema_tables_memory_usage(TABLE_LIST *table_list)
+{
+  TABLE *table= table_list->table;
+  THD *thd=table->in_use;
+  if (!table->is_created())
+  {
+    TMP_TABLE_PARAM *p= table_list->schema_table_param;
+    TMP_ENGINE_COLUMNDEF *from_recinfo, *to_recinfo;
+    DBUG_ASSERT(table->s->keys == 0);
+    DBUG_ASSERT(table->s->uniques == 0);
+
+    // XXX HACK HACK HACK: in a stored function, RETURN (SELECT ...)
+    // enables warnings (in THD::sp_eval_expr) for the whole val_xxx/store pair,
+    // while the intention is to warn only for store(). Until this is
+    // fixed let's avoid data truncation warnings in I_S->fill_table()
+    if (thd->count_cuted_fields == CHECK_FIELD_IGNORE)
+    {
+
+    uchar *cur= table->field[0]->ptr;
+    /* first recinfo could be a NULL bitmap, not an actual Field */
+    from_recinfo= to_recinfo= p->start_recinfo + (cur != table->record[0]);
+    for (uint i=0; i < table->s->fields; i++, from_recinfo++)
+    {
+      Field *field= table->field[i];
+      DBUG_ASSERT(field->vcol_info == 0);
+      DBUG_ASSERT(from_recinfo->length= field->pack_length_in_rec());
+      if (bitmap_is_set(table->read_set, i))
+      {
+        field->move_field(cur);
+        *to_recinfo++= *from_recinfo;
+        cur+= from_recinfo->length;
+      }
+      else
+      {
+        field= new (thd->mem_root) Field_string(cur, 0, field->null_ptr,
+                              field->null_bit, Field::NONE,
+                              &field->field_name, field->dtcollation());
+        field->init(table);
+        field->field_index= i;
+        DBUG_ASSERT(field->pack_length_in_rec() == 0);
+        table->field[i]= field;
+      }
+    }
+    if ((table->s->reclength= (ulong)(cur - table->record[0])) == 0)
+    {
+      /* all fields were optimized away. Force a non-0-length row */
+      table->s->reclength= to_recinfo->length= 1;
+      to_recinfo++;
+    }
+    p->recinfo= to_recinfo;
+    } // XXX end of HACK HACK HACK
+
+    // TODO switch from Aria to Memory if all blobs were optimized away?
+    if (instantiate_tmp_table(table, p->keyinfo, p->start_recinfo, &p->recinfo,
+                 table_list->select_lex->options | thd->variables.option_bits))
+      return 1;
+  }
+  return 0;
+}
+
+
 /*
   This is the optimizer part of get_schema_tables_result().
 */
@@ -8771,6 +8744,9 @@ bool optimize_schema_tables_reads(JOIN *join)
     TABLE_LIST *table_list= tab->table->pos_in_table_list;
     if (table_list->schema_table && thd->fill_information_schema_tables())
     {
+      if (optimize_schema_tables_memory_usage(table_list))
+        DBUG_RETURN(1);
+
       /* A value of 0 indicates a dummy implementation */
       if (table_list->schema_table->fill_table == 0)
         continue;