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<p>
<span class="bold"><strong>What priorities should
threads/tasks executing Berkeley DB functions be
given?</strong></span>
</p>
<p>
Tasks executing Berkeley DB functions should have
the same, or roughly equivalent, system priorities.
For example, it can be dangerous to give tasks of
control performing checkpoints a lower priority than
tasks of control doing database lookups, and
starvation can sometimes result.
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<li>
<p>
<span class="bold"><strong>Why isn't the C++ API exception
safe?</strong></span>
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<p>
The Berkeley DB C++ API is a thin wrapper around
the C API that maps most return values to exceptions,
and gives the C++ handles the same lifecycles as their
C counterparts. One consequence is that if an
exception occurs while a cursor or transaction handle
is open, the application must explicitly close the
cursor or abort the transaction.
</p>
<p>
Applications can be simplified and bugs avoided by
creating wrapper classes around <a href="../api_reference/C/dbc.html" class="olink">DBC</a> and <a href="../api_reference/C/txn.html" class="olink">TXN</a> that
call the appropriate cleanup method in the wrapper's
destructor. By creating an instance of the wrappers on
the stack, C++ scoping rules will ensure that the
destructor is called before exception handling unrolls
the block that contains the wrapper object.
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<p>
<span class="bold"><strong> How do I handle a "pass 4"
error when trying to run one of the example
Performance Event Monitoring scripts on my Linux
system? The library was configured with
<code class="literal">--enable-dtrace</code> and built
without error. </strong></span>
</p>
<p>
A Linux installation can have SystemTap support for
kernel probe points without including the kernel
"utrace" module needed to use userspace probes. Pass 4
errors can occur when this required userspace support
is not present.
</p>
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<p>
<span class="bold"><strong> I have a program with multiple
threads running on multi-core systems, and it uses
a shared DB handle for all the threads. The
program does not behave as well as I expect and I
see a lot of contention on the dbp->mutex, what
should I do to reduce this contention ?
</strong></span>
</p>
<p>
When running multi-threaded program on a
multi-core/multi-processor system, we suggest using a
DB handle per thread instead of using a shared handle
accorss threads. Since many operations(like creating
cursors) requires to lock the DB handle first, and if
using a shared handle, there could be a lot of lock
contention on the handle.
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