Description:
The Falcon storage engine does not detect if its tablespace files have gone missing. It
will recreate them (and maybe apply the serial log), at which point there will be an
inconsistency between the server metadata and the Falcon metadata.

Server will still list the tables in SHOW TABLES, however SHOW TABLE STATUS will report no
tables. No error message will be written to the error log.

In contrast, when faced with the same situation, Innodb will report:

080519  4:51:26 [ERROR] Cannot find or open table test/i from
the internal data dictionary of InnoDB though the .frm file for the
table exists. Maybe you have deleted and recreated InnoDB data
files but have forgotten to delete the corresponding .frm files
of InnoDB tables, or you have moved .frm files to another database?
or, the table contains indexes that this version of the engine
doesn't support.
See http://dev.mysql.com/doc/refman/5.1/en/innodb-troubleshooting.html
how you can resolve the problem.

How to repeat:
1. Start server

$ ./mysqld --language=/build/6.0-falcon-team/sql/share/english/ --innodb
--datadir=/build/datadir --skip-grant-tables --falcon_debug_mask=65535

2. Create tables
create database test;
create table test.f (f1 integer) engine=falcon;
create table test.i (f1 integer) engine=innodb;

3. Shutdown server

4. Delete Falcon and Innodb files:

rm -f datadir/falcon*
rm -f datadir/ib*

5. Restart server (same as step #1)

6. Run queries:

> SHOW TABLE STATUS; -- returns empty list, Innodb complains vocally in error log
> SELECT * FROM f; -- complains table does not exist, Falcon puts nothing in the log
> SELECT * FROM i; -- complains table does not exist, Innodb complains vocally in error
log
> DROP TABLE f; -- succeeds, Falcon log message "Exception: can't find table "TEST.F" in
log
> DROP TABLE i; -- complains table does not exist, long message from Innodb in log.

Suggested fix:
If it is not possible to prevent the server from starting altogether, than at least:

* complain in log when metadata is messed up;
* prevent tables that are not there from being dropped sucessfully;

What we need here is an error from Falcon that indicates the tablespace is not found

A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/commits/58010

2905 Sergey Vojtovich	2008-11-06
      BUG#36804 - Falcon does not detect deleted tablespace files
      
      Falcon silently recreates it's system data files if it wasn't
      able to open them. With this fix Falcon provides some
      additional information in error log.
      
      When starting mysql server with Falcon and we were unable
      to open Falcon system data files, write a warning to error
      log.
      
      Write an error message to error log when attempting to access
      a table that doesn't exist in Falcon.

A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/commits/58455

2905 Sergey Vojtovich	2008-11-11
      BUG#36804 - Falcon does not detect deleted tablespace files
      
      Falcon silently recreates it's system data files if it wasn't
      able to open them. With this fix Falcon provides some
      additional information in error log.
      
      When starting mysql server with Falcon and we were unable
      to open Falcon system data files, write a warning to error
      log.
      
      Write an error message to error log when attempting to access
      a table that doesn't exist in Falcon.

A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/commits/58649

2905 Sergey Vojtovich	2008-11-13
      BUG#36804 - Falcon does not detect deleted tablespace files
      
      Falcon silently recreates it's system data files if it wasn't
      able to open them. With this fix Falcon provides some
      additional information in error log.
      
      When starting mysql server with Falcon and we were unable
      to open Falcon system data files, write a warning to error
      log.
      
      Write an error message to error log when attempting to access
      a table that doesn't exist in Falcon.

Was approved by Kevin.

Pushed into 6.0.9-alpha  (revid:svoj@mysql.com-20081113132713-ax39hfodu75yjgzr) (version
source revid:svoj@mysql.com-20081114103602-9ka2uls5cck9k1oq) (pib:5)

A note has been added to the 6.0.9 changelog: 

The FALCON storage would silently recreate missing tablespace files if they did not exist.
Errors are now written to the MySQL error log when the FALCON system tablespace files are
found to be missing. Warnings are produce in the log file when attempting to access data
tablespace files that do not exist.