Avoid creating the .frm file twice in some cases

Other things:
- Updated code comments & fixed indentation
- Removed an old QQ (temporary) comment that does not apply anymore

sql/datadict.cc

@@ -194,6 +194,6 @@ bool dd_recreate_table(THD *thd, const char *db, const char *table_name)
   build_table_filename(path_buf, sizeof(path_buf) - 1,
                        db, table_name, "", 0);
   /* Attempt to reconstruct the table. */
-  DBUG_RETURN(ha_create_table(thd, path_buf, db, table_name, &create_info, 0));
+  DBUG_RETURN(ha_create_table(thd, path_buf, db, table_name, &create_info, 0, 0));
 }
 

sql/handler.cc

@@ -5525,9 +5525,9 @@ int handler::calculate_checksum()
   @retval
    1  error
 */
-int ha_create_table(THD *thd, const char *path,
-                    const char *db, const char *table_name,
-                    HA_CREATE_INFO *create_info, LEX_CUSTRING *frm)
+int ha_create_table(THD *thd, const char *path, const char *db,
+                    const char *table_name, HA_CREATE_INFO *create_info,
+                    LEX_CUSTRING *frm, bool skip_frm_file)
 {
   int error= 1;
   TABLE table;
@@ -5543,8 +5543,8 @@ int ha_create_table(THD *thd, const char *path,
 
   if (frm)
   {
-    bool write_frm_now= !create_info->db_type->discover_table &&
-                        !create_info->tmp_table();
+    bool write_frm_now= (!create_info->db_type->discover_table &&
+                         !create_info->tmp_table() && !skip_frm_file);
 
     share.frm_image= frm;
 

sql/handler.h

@@ -5172,9 +5172,9 @@ bool ha_flush_logs();
 void ha_drop_database(char* path);
 void ha_checkpoint_state(bool disable);
 void ha_commit_checkpoint_request(void *cookie, void (*pre_hook)(void *));
-int ha_create_table(THD *thd, const char *path,
-                    const char *db, const char *table_name,
-                    HA_CREATE_INFO *create_info, LEX_CUSTRING *frm);
+int ha_create_table(THD *thd, const char *path, const char *db,
+                    const char *table_name, HA_CREATE_INFO *create_info,
+                    LEX_CUSTRING *frm, bool skip_frm_file);
 int ha_delete_table(THD *thd, handlerton *db_type, const char *path,
                     const LEX_CSTRING *db, const LEX_CSTRING *alias,
                     bool generate_warning);

sql/item_vers.h

@@ -46,7 +46,7 @@ class Item_func_history: public Item_bool_func
   LEX_CSTRING func_name_cstring() const override
   {
     static LEX_CSTRING name= {STRING_WITH_LEN("is_history") };
-   return name;
+    return name;
   }
   void print(String *str, enum_query_type query_type) override;
   Item *get_copy(THD *thd) override

sql/sql_table.cc

@@ -549,8 +549,13 @@ uint build_table_filename(char *buff, size_t bufflen, const char *db,
 
   (void) tablename_to_filename(db, dbbuff, sizeof(dbbuff));
 
-  /* Check if this is a temporary table name. Allow it if a corresponding .frm file exists */
-  if (is_prefix(table_name, tmp_file_prefix) && strlen(table_name) < NAME_CHAR_LEN &&
+  /*
+    Check if this is a temporary table name. Allow it if a corresponding .frm
+    file exists.
+  */
+  if (!(flags & FN_IS_TMP) &&
+      is_prefix(table_name, tmp_file_prefix) &&
+      strlen(table_name) < NAME_CHAR_LEN &&
       check_if_frm_exists(tbbuff, dbbuff, table_name))
     flags|= FN_IS_TMP;
 
@@ -3997,13 +4002,17 @@ handler *mysql_create_frm_image(THD *thd, const LEX_CSTRING &db,
                              the extension).
   @param create_info         Create information (like MAX_ROWS)
   @param alter_info          Description of fields and keys for new table
-  @param create_table_mode   C_ORDINARY_CREATE, C_ALTER_TABLE, C_ASSISTED_DISCOVERY
+  @param create_table_mode   C_ORDINARY_CREATE, C_ALTER_TABLE,
+                             C_ASSISTED_DISCOVERY or C_ALTER_TABLE_FRM_ONLY.
                              or any positive number (for C_CREATE_SELECT).
+                             If set to C_ALTER_TABLE_FRM_ONY then no frm or
+                             table is created, only the frm image in memory.
   @param[out] is_trans       Identifies the type of engine where the table
                              was created: either trans or non-trans.
   @param[out] key_info       Array of KEY objects describing keys in table
                              which was created.
   @param[out] key_count      Number of keys in table which was created.
+  @param[out] frm            The frm image.
 
   If one creates a temporary table, its is automatically opened and its
   TABLE_SHARE is added to THD::all_temp_tables list.
@@ -4264,7 +4273,8 @@ int create_table_impl(THD *thd, const LEX_CSTRING &orig_db,
 
     if (!frm_only)
     {
-      if (ha_create_table(thd, path, db.str, table_name.str, create_info, frm))
+      if (ha_create_table(thd, path, db.str, table_name.str, create_info,
+                          frm, 0))
       {
         file->ha_create_partitioning_metadata(path, NULL, CHF_DELETE_FLAG);
         deletefrm(path);
@@ -7083,18 +7093,14 @@ static bool mysql_inplace_alter_table(THD *thd,
           goto rollback;
         }
         if (trt.update(trx_start_id, trx_end_id))
-        {
           goto rollback;
-        }
       }
     }
 
     if (table->file->ha_commit_inplace_alter_table(altered_table,
                                                   ha_alter_info,
                                                   true))
-    {
       goto rollback;
-    }
     DEBUG_SYNC(thd, "alter_table_inplace_after_commit");
   }
 
@@ -7197,7 +7203,6 @@ static bool mysql_inplace_alter_table(THD *thd,
                               NULL);
     if (thd->locked_tables_list.reopen_tables(thd, false))
       thd->locked_tables_list.unlink_all_closed_tables(thd, NULL, 0);
-    /* QQ; do something about metadata locks ? */
   }
   DBUG_RETURN(true);
 }
@@ -8709,6 +8714,7 @@ simple_rename_or_index_change(THD *thd, TABLE_LIST *table_list,
   {
     THD_STAGE_INFO(thd, stage_rename);
     handlerton *old_db_type= table->s->db_type();
+
     /*
       Then do a 'simple' rename of the table. First we need to close all
       instances of 'source' table.
@@ -8878,7 +8884,7 @@ bool mysql_alter_table(THD *thd, const LEX_CSTRING *new_db,
                        uint order_num, ORDER *order, bool ignore,
                        bool if_exists)
 {
-  bool engine_changed, error;
+  bool engine_changed, error, frm_is_created= false;
   bool no_ha_table= true;  /* We have not created table in storage engine yet */
   TABLE *table, *new_table;
 #ifdef WITH_PARTITION_STORAGE_ENGINE
@@ -9633,6 +9639,11 @@ do_continue:;
     if (create_table_for_inplace_alter(thd, alter_ctx, &frm, &altered_share,
                                        &altered_table))
       goto err_new_table_cleanup;
+    /*
+      Avoid creating frm again in ha_create_table() if inline alter will not
+      be used.
+    */
+    frm_is_created= 1;
 
     /* Set markers for fields in TABLE object for altered table. */
     update_altered_table(ha_alter_info, &altered_table);
@@ -9764,7 +9775,7 @@ do_continue:;
 
   if (ha_create_table(thd, alter_ctx.get_tmp_path(),
                       alter_ctx.new_db.str, alter_ctx.new_name.str,
-                      create_info, &frm))
+                      create_info, &frm, frm_is_created))
     goto err_new_table_cleanup;
 
   /* Mark that we have created table in storage engine. */
@@ -9867,7 +9878,7 @@ do_continue:;
 
   if (table->s->tmp_table != NO_TMP_TABLE)
   {
-    /* Close lock if this is a transactional table */
+    /* Release lock if this is a transactional temporary table */
     if (thd->lock)
     {
       if (thd->locked_tables_mode != LTM_LOCK_TABLES &&
@@ -9888,6 +9899,7 @@ do_continue:;
           goto err_new_table_cleanup;
       }
     }
+
     new_table->s->table_creation_was_logged=
       table->s->table_creation_was_logged;
     /* Remove link to old table and rename the new one */