mirror of
https://github.com/yasuhirokimura/db18
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Yasuhiro KIMURA
142 lines
6.2 KiB
HTML
142 lines
6.2 KiB
HTML
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>Programmer notes FAQ</title>
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<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
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<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
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<link rel="start" href="index.html" title="Berkeley DB Programmer's Reference Guide" />
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<link rel="up" href="program.html" title="Chapter 17. Programmer Notes" />
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<link rel="prev" href="program_perfmon.html" title="Performance Event Monitoring" />
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<link rel="next" href="lock.html" title="Chapter 18. The Locking Subsystem" />
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</head>
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<body>
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<div xmlns="" class="navheader">
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<div class="libver">
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<p>Library Version 18.1.32</p>
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</div>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">Programmer notes FAQ</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="program_perfmon.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 17. Programmer Notes </th>
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<td width="20%" align="right"> <a accesskey="n" href="lock.html">Next</a></td>
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</tr>
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</table>
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<hr />
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</div>
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<div class="sect1" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title" style="clear: both"><a id="program_faq"></a>Programmer notes FAQ</h2>
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</div>
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</div>
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</div>
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<div class="orderedlist">
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<ol type="1">
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<li>
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<p>
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<span class="bold"><strong>What priorities should
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threads/tasks executing Berkeley DB functions be
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given?</strong></span>
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</p>
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<p>
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Tasks executing Berkeley DB functions should have
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the same, or roughly equivalent, system priorities.
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For example, it can be dangerous to give tasks of
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control performing checkpoints a lower priority than
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tasks of control doing database lookups, and
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starvation can sometimes result.
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</p>
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</li>
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<li>
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<p>
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<span class="bold"><strong>Why isn't the C++ API exception
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safe?</strong></span>
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</p>
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<p>
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The Berkeley DB C++ API is a thin wrapper around
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the C API that maps most return values to exceptions,
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and gives the C++ handles the same lifecycles as their
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C counterparts. One consequence is that if an
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exception occurs while a cursor or transaction handle
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is open, the application must explicitly close the
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cursor or abort the transaction.
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</p>
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<p>
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Applications can be simplified and bugs avoided by
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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
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call the appropriate cleanup method in the wrapper's
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destructor. By creating an instance of the wrappers on
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the stack, C++ scoping rules will ensure that the
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destructor is called before exception handling unrolls
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the block that contains the wrapper object.
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</p>
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</li>
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<li>
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<p>
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<span class="bold"><strong> How do I handle a "pass 4"
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error when trying to run one of the example
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Performance Event Monitoring scripts on my Linux
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system? The library was configured with
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<code class="literal">--enable-dtrace</code> and built
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without error. </strong></span>
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</p>
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<p>
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A Linux installation can have SystemTap support for
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kernel probe points without including the kernel
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"utrace" module needed to use userspace probes. Pass 4
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errors can occur when this required userspace support
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is not present.
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</p>
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</li>
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<li>
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<p>
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<span class="bold"><strong> I have a program with multiple
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threads running on multi-core systems, and it uses
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a shared DB handle for all the threads. The
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program does not behave as well as I expect and I
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see a lot of contention on the dbp->mutex, what
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should I do to reduce this contention ?
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</strong></span>
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</p>
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<p>
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When running multi-threaded program on a
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multi-core/multi-processor system, we suggest using a
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DB handle per thread instead of using a shared handle
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accorss threads. Since many operations(like creating
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cursors) requires to lock the DB handle first, and if
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using a shared handle, there could be a lot of lock
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contention on the handle.
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</p>
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</li>
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</ol>
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</div>
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</div>
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<div class="navfooter">
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<hr />
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<table width="100%" summary="Navigation footer">
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<tr>
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<td width="40%" align="left"><a accesskey="p" href="program_perfmon.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="program.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="lock.html">Next</a></td>
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</tr>
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<tr>
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<td width="40%" align="left" valign="top">Performance Event
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Monitoring </td>
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<td width="20%" align="center">
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<a accesskey="h" href="index.html">Home</a>
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</td>
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<td width="40%" align="right" valign="top"> Chapter 18. The Locking Subsystem </td>
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</tr>
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</table>
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</div>
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</body>
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</html>
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