Kazuho at Work

    int4store(follower_keybuff, user_id);
    if (follower_tbl->file->index_read_map(follower_tbl->record[0],
					   follower_keybuff, 1, HA_READ_PREFIX)
	== 0) {
      do {
	unsigned follower_id = follower_follower_id_fld->val_int();
	int4store(message_keybuff, follower_id);
	if (message_tbl->file->index_read_map(message_tbl->record[0],
					      message_keybuff, 1,
					      HA_READ_PREFIX_LAST)
	    == 0) {
	  do {
	    if (! test_add_id(message_id_fld->val_int())) {
	      break;
	    }
	  } while (message_tbl->file->index_prev(message_tbl->record[0]) == 0
		   && message_user_id_fld->val_int() == follower_id);
	}
      } while (follower_tbl->file->index_next(follower_tbl->record[0]) == 0
	       && follower_user_id_fld->val_int() == user_id);
    }

To use the code, all you have to do is to compile to a shared library, and install it as an ordinal UDF.

% g++ -I ~/dev/mysql/51/32-src/include -I ~/dev/mysql/51/32-src/sql -I ~/dev/mysql/51/32-src/regex -g -Wall -O1 -fno-rtti -fno-exceptions  -shared -o timeline.so timeline.cc
(snip)
% cp timeline.so ~/dev/mysql/51/32-bin/lib/plugin
% mysql -u root -p test
mysql> CREATE FUNCTION timeline returns int soname 'timeline.so';
Query OK, 0 rows affected (0.00 sec)

mysql> CREATE TEMPORARY TABLE fetch_timeline_tt (id int unsigned NOT NULL) ENGINE=heap;
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT timeline(123);

mysql> SELECT message.* FROM message INNER JOIN fetch_timeline_tt USING (id);

And it returns the timeline for user id 123. A quick hack, but easy to implement, and very fast. No more need for writing custom servers. Whenever SQL doesn't do well, I can just call InnoDB directly.