So… in removing the FRM file in Drizzle, I found a bit of a nugget on how drop table works (currently in the MySQL server and now “did” in Drizzle).

If you DROP TABLE t1; this is what happens

• open the .frm file
• read first 10bytes (oh, and if you get EIO there, in a SELECT * FROM INFORMATION_SCHEMA.TABLES you’ll get “Error” instead of “Base Table”)
• if (header[0] != (unsigned char) 254 || header[1] != 1 ||
  (header[2] != FRM_VER && header[2] != FRM_VER+1 &&
  (header[2] < FRM_VER+3 || header[2] > FRM_VER+4)))
  return true;
  Which means that you probably (well, should have) set your enum legacy_db_type to DB_TYPE_UNKNOWN in the caller of bool mysql_frm_type(Session *, char *path, enum legacy_db_type *dbt) otherwise you end up in some form of pain.
• Else, *dbt= (enum legacy_db_type) (uint) *(header + 3);
  return true;                   // Is probably a .frm table

I do like the “probably”.

Oh, and on a “storage engine api” front, some places seem to expect handler::delete_table(const char* name) to return ENOENT on table not existing. In reality however:

• int ha_heap::delete_table(const char *name)
  {
  -  int error= heap_delete_table(name);
  -  return error == ENOENT ? 0 : error;
  +  return heap_delete_table(name);
  }
• InnoDB (note the behaviour of returning DB_TABLE_NOT_FOUND… which isn’t ENOENT)
  err = DB_TABLE_NOT_FOUND;
  ut_print_timestamp(stderr);

  fputs(“  InnoDB: Error: table “, stderr);
  ut_print_name(stderr, trx, TRUE, name);
  fputs(” does not exist in the InnoDB internaln”
  “InnoDB: data dictionary though MySQL is”
  ” trying to drop it.n”
  “InnoDB: Have you copied the .frm file”
  ” of the table to then”
  “InnoDB: MySQL database directory”
  ” from another database?n”
  “InnoDB: You can look for further help fromn”
  “InnoDB: http://dev.mysql.com/doc/refman/5.1/en/”
  “innodb-troubleshooting.htmln”,
  stderr);

• and MyISAM would generate the error message itself, but that’s fixed with:
  -  if (my_delete_with_symlink(from, MYF(MY_WME)))
  +  if (my_delete_with_symlink(from, 0))
  return(my_errno);

and just to add to the fun, elsewhere in the code, a access(2) call on the frm file name is used to determine if the table exists or not.

The road to removing the FRM has all sorts of these weird-ass things along it. Kinda nice to be able to replace this with something better (and, hopefully – good).

But let me sum up with sql_table.cc:

“This code is wrong and will be removed, please do not copy.”