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110 lines
4.6 KiB
HTML
110 lines
4.6 KiB
HTML
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<?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 15. 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 16. 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 11.2.5.2</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 15.
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Programmer Notes
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</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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<span class="bold">
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<strong>What priorities should threads/tasks executing Berkeley DB functions
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be given?</strong>
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</span>
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<p>Tasks executing Berkeley DB functions should have the same, or roughly
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equivalent, system priorities. For example, it can be dangerous to give
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tasks of control performing checkpoints a lower priority than tasks of
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control doing database lookups, and starvation can sometimes result.</p>
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</li>
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<li>
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<span class="bold">
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<strong>Why isn't the C++ API exception safe?</strong>
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</span>
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<p>The Berkeley DB C++ API is a thin wrapper around the C API that maps most
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return values to exceptions, and gives the C++ handles the same
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lifecycles as their C counterparts. One consequence is that if an
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exception occurs while a cursor or transaction handle is open, the
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application must explicitly close the cursor or abort the transaction.</p>
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<p>Applications can be simplified and bugs avoided by creating wrapper
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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
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cleanup method in the wrapper's destructor. By creating an instance
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of the wrappers on the stack, C++ scoping rules will ensure that the
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destructor is called before exception handling unrolls the block that
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contains the wrapper object.</p>
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</li>
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<li>
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<span class="bold">
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<strong>
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How do I handle a "pass 4" error when trying to run one of the
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example Performance Event Monitoring scripts on my Linux system?
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The library configured with --enable-dtrace and built without error.
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</strong>
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</span>
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<p>
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A Linux installation can have SystemTap support for kernel probe points
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without including the kernel "utrace" module needed to use userspace
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probes. Pass 4 errors can occur when this required userspace
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support is not present.
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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 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 16.
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The Locking Subsystem
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</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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