Error in generating BdB:tree

Question

Hi,
I don't have much experience using BDB's (or perl), but currently I'm working on storing a huge collection of data into one via perl. I'm using a combination of Records and Btrees, and have recently ran into a problem where when I try retrieving a tied handle to a BDB subdatabase, I run into following error:
No such file or directory subname: unexpected file type or format
Where subname is the db that I'm querying for.
When I ran db_verify against the bdb, it returned the following message:
db_verify: Subdatabase entry references page 11188 of invalid type 5
db_verify: DB->verify: daily_percs_log.db: DB_VERIFY_BAD: Database verification failed
which tells me that the data in the bdb is probably corrupt.
Would anyone have any idea why this is happening?
The program that I wrote isn't multi-threaded, so I shouldn't have to worry about using transactions, right?

Answer 1

Hi,
For recoverability you should use transactions and logging. In addition, unless you're using the subdatabases (logical databases in a single physical file) in read-only mode, then you need to enable locking. Even if you're running single-threaded locking is needed as there may be conflicts during page allocation.
Enabling the transaction, logging and locking subsystems implies using a database environment, and moreover, if any of the subdatabases in the file is opened for update, all of the subdatabases in the file must share a memory pool (the memory pool subsystem need to be enabled).
Here is more information on subdatabases:
http://www.oracle.com/technology/documentation/berkeley-db/db/ref/am/opensub.html
The Reference Guide is a good place to get information on architecting a transactional application:
http://www.oracle.com/technology/documentation/berkeley-db/db/ref/toc.html
Now, since you don't have any logs around to recover, and probably no recent snapshot that on top of which to reiterate the last changes (if possible), the solution is to do a salvage dump (-r or -R) / reload of the data if you cannot recreate the databases from scratch:
http://www.oracle.com/technology/documentation/berkeley-db/db/ref/dumpload/utility.html
http://www.oracle.com/technology/documentation/berkeley-db/db/utility/db_dump.html
http://www.oracle.com/technology/documentation/berkeley-db/db/utility/db_load.html
Regards,
Andrei