Database.exists fails with "illegal flag specified to DB- exists" in 4.7.25

Question

Hello all!
We are using the Java interface to the C based Oracle Berkeley DB version 4.7.25 under Solaris, Linux, and Winwoes XP, all using a 32-bit address space.
Our code is calling Database.get just to check to see if a key exists in the database.
That is working.
When I change our code to call Database.exists (as recommended in the FAQ) I get the error "illegal flag specified to DB->exists":
<blockquote><pre>
java.lang.IllegalArgumentException: Invalid argument: illegal flag specified to DB->exists
at com.sleepycat.db.internal.db_javaJNI.Db_exists(Native Method)
at com.sleepycat.db.internal.Db.exists(Db.java:323)
at com.sleepycat.db.Database.exists(Database.java:584)
</pre></blockquote>
In the call to Database.exists I am passing null for the txn parameter, just like the call to Database.get did.
If I construct a Transaction object and pass that in the call to Database.exists, exists works correctly.
Looking at the Berkeley DB source code for Database.exists shows the Java wrapper adds a flag if the txn parameter is null:
<blockquote><pre>
return OperationStatus.fromInt(
db.exists((txn == null) ? null : txn.txn, key,
((txn == null) ? autoCommitFlag : 0)));
</pre></blockquote>
The autoCommitFlag is initialized to DbConstants.DB_AUTO_COMMIT by the Database class if transactions are enabled for the database, which they are in our case.
The method __db_exists in the Berkeley DB C code does not accept the DB_AUTO_COMMIT:
<blockquote><pre>
     if ((ret = __db_fchk(dbp->env, "DB-\>exists", flags,
     DB_READ_COMMITTED | DB_READ_UNCOMMITTED | DB_RMW)) != 0)
          return (ret);
</pre></blockquote>
In the Berkeley DB Reference Guide found here:
[http://www.oracle.com/technology/documentation/berkeley-db/db/ref/upgrade.4.4/autocommit.html]
There is this statement concerning the DB_AUTO_COMMIT flag and changes in 4.4:
<blockquote>
In previous Berkeley DB releases, the DB_AUTO_COMMIT flag was used in the C and C++ Berkeley DB APIs to wrap operations within a transaction without explicitly creating a transaction and passing the DB_TXN handle as part of the operation method call. In the 4.4 release, the DB_AUTO_COMMIT flag no longer needs to be explicitly specified.
</blockquote>
It also says:
<blockquote>
No related application changes are required for this release, as the DB_AUTO_COMMIT flag is ignored where it is no longer needed. However, application writers are encouraged to remove uses of the DB_AUTO_COMMIT flag in places where it is no longer needed.
</blockquote>
Maybe the situation has changed since 4.4, but that text from the reference manual seems to indicate that the Berkeley DB Database.exists Java code should not be passing the DB_AUTO_COMMIT flag and the Berkeley DB C method __db_exists must ignore DB_AUTO_COMMIT if it is passed.
Does this represent a defect in Oracle Berkeley DB, or has the situation changed in 4.7?
Thanks for any help!
Greg

Answer 1

Hi Greg, thanks for the thorough diagnosis! You've definitely found a bug in BDB, we are currently validating a patch and hope to have it available for you soon.
Ben Schmeckpeper