Interbase transaction number bug

While performing a necropsy on a database recently, I ran into a bug which may be of interest to some people.

Attempts to attach to the database failed with the error "gds internal consistency check, can't find tip." Checking the database header showed that the next transaction number was 131,596,294 and the page size was 1024. As it happens, a 1024 byte page will hold 4016 transaction states. Dividing the next transaction number by 4016 to get the tip page sequence number gives 32768.001494. A very interesting number.

There is a bug in InterBase 5.6, 6.01, and the current Firebird beta that causes the lookup of a transaction inventory page to fail if there are more than 32767 transaction pages. That makes the maximum safe transaction id for a database with:

   1024 byte pages 131,596,287.
   2048 byte pages 265,814,016.
   4096 byte pages 534,249,472.
   8192 byte pages 1,071,120,384.

Although those are large numbers, this particular
database exceeded 131 million transactions in six
months.

Suggestions:


  1. don't use a 1024 byte page size.
  2. do check your next transaction number from time to time.
  3. if you see the next transaction number approaching the limit, backup and restore the database.
  4. Gfix won't fix this problem, but I can. (Please contact me for details).

    Regards,

    Ann

 

Share this article!

Follow us!

Find more helpful articles: