mirror of
https://github.com/berkeleydb/libdb.git
synced 2024-11-17 01:26:25 +00:00
367 lines
16 KiB
HTML
367 lines
16 KiB
HTML
|
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
|
|||
|
|
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
|
|||
|
|
<html xmlns="http://www.w3.org/1999/xhtml">
|
|||
|
|
<head>
|
|||
|
|
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
|
|||
|
|
<title>Permanent Message Handling</title>
|
|||
|
|
<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
|
|||
|
|
<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
|
|||
|
|
<link rel="start" href="index.html" title="Getting Started with Replicated Berkeley DB Applications" />
|
|||
|
|
<link rel="up" href="repapp.html" title="Chapter 3. The DB Replication Manager" />
|
|||
|
|
<link rel="prev" href="repmgr_init_example_c.html" title="Adding the Replication Manager to SimpleTxn" />
|
|||
|
|
<link rel="next" href="electiontimes.html" title="Managing Election Times" />
|
|||
|
|
</head>
|
|||
|
|
<body>
|
|||
|
|
<div xmlns="" class="navheader">
|
|||
|
|
<div class="libver">
|
|||
|
|
<p>Library Version 11.2.5.2</p>
|
|||
|
|
</div>
|
|||
|
|
<table width="100%" summary="Navigation header">
|
|||
|
|
<tr>
|
|||
|
|
<th colspan="3" align="center">Permanent Message Handling</th>
|
|||
|
|
</tr>
|
|||
|
|
<tr>
|
|||
|
|
<td width="20%" align="left"><a accesskey="p" href="repmgr_init_example_c.html">Prev</a> </td>
|
|||
|
|
<th width="60%" align="center">Chapter 3. The DB Replication Manager</th>
|
|||
|
|
<td width="20%" align="right"> <a accesskey="n" href="electiontimes.html">Next</a></td>
|
|||
|
|
</tr>
|
|||
|
|
</table>
|
|||
|
|
<hr />
|
|||
|
|
</div>
|
|||
|
|
<div class="sect1" lang="en" xml:lang="en">
|
|||
|
|
<div class="titlepage">
|
|||
|
|
<div>
|
|||
|
|
<div>
|
|||
|
|
<h2 class="title" style="clear: both"><a id="fwrkpermmessage"></a>Permanent Message Handling</h2>
|
|||
|
|
</div>
|
|||
|
|
</div>
|
|||
|
|
</div>
|
|||
|
|
<div class="toc">
|
|||
|
|
<dl>
|
|||
|
|
<dt>
|
|||
|
|
<span class="sect2">
|
|||
|
|
<a href="fwrkpermmessage.html#fmwrkpermpolicy">Identifying Permanent Message Policies</a>
|
|||
|
|
</span>
|
|||
|
|
</dt>
|
|||
|
|
<dt>
|
|||
|
|
<span class="sect2">
|
|||
|
|
<a href="fwrkpermmessage.html#fmwrkpermtimeout">Setting the Permanent Message Timeout</a>
|
|||
|
|
</span>
|
|||
|
|
</dt>
|
|||
|
|
<dt>
|
|||
|
|
<span class="sect2">
|
|||
|
|
<a href="fwrkpermmessage.html#perm2fmwrkexample">Adding a Permanent Message Policy to
|
|||
|
|
|
|||
|
|
|
|||
|
|
<span>RepQuoteExampleGSG</span>
|
|||
|
|
</a>
|
|||
|
|
</span>
|
|||
|
|
</dt>
|
|||
|
|
</dl>
|
|||
|
|
</div>
|
|||
|
|
<p>
|
|||
|
|
As described in <a class="xref" href="permmessages.html" title="Permanent Message Handling">Permanent Message Handling</a>,
|
|||
|
|
messages are marked permanent if they contain database
|
|||
|
|
modifications that should be committed at the replica.
|
|||
|
|
DB's replication code decides if it must flush its
|
|||
|
|
transaction logs to disk depending on whether it receives
|
|||
|
|
sufficient permanent message acknowledgments from the
|
|||
|
|
participating replicas. More importantly, the thread
|
|||
|
|
performing the transaction commit blocks
|
|||
|
|
until it either receives enough acknowledgments, or the
|
|||
|
|
acknowledgment timeout expires.
|
|||
|
|
</p>
|
|||
|
|
<p>
|
|||
|
|
The Replication Manager is fully capable of managing permanent messages
|
|||
|
|
for you if your application requires it (most do).
|
|||
|
|
Almost all of the details of this are handled by the
|
|||
|
|
Replication Manager for you. However, you do have to set some policies
|
|||
|
|
that tell the Replication Manager how to handle permanent messages.
|
|||
|
|
</p>
|
|||
|
|
<p>
|
|||
|
|
There are two things that you have to do:
|
|||
|
|
</p>
|
|||
|
|
<div class="itemizedlist">
|
|||
|
|
<ul type="disc">
|
|||
|
|
<li>
|
|||
|
|
<p>
|
|||
|
|
Determine how many acknowledgments
|
|||
|
|
must be received by the master.
|
|||
|
|
</p>
|
|||
|
|
</li>
|
|||
|
|
<li>
|
|||
|
|
<p>
|
|||
|
|
Identify the amount of time that
|
|||
|
|
replicas have to send their
|
|||
|
|
acknowledgments.
|
|||
|
|
</p>
|
|||
|
|
</li>
|
|||
|
|
</ul>
|
|||
|
|
</div>
|
|||
|
|
<div class="sect2" lang="en" xml:lang="en">
|
|||
|
|
<div class="titlepage">
|
|||
|
|
<div>
|
|||
|
|
<div>
|
|||
|
|
<h3 class="title"><a id="fmwrkpermpolicy"></a>Identifying Permanent Message Policies</h3>
|
|||
|
|
</div>
|
|||
|
|
</div>
|
|||
|
|
</div>
|
|||
|
|
<p>
|
|||
|
|
|
|||
|
|
You identify permanent message policies using the
|
|||
|
|
|
|||
|
|
|
|||
|
|
<span>
|
|||
|
|
<code class="classname">ReplicationManagerAckPolicy</code>
|
|||
|
|
class which you pass to the environment
|
|||
|
|
using the
|
|||
|
|
<code class="methodname">EnvironmentConfig.setReplicationManagerAckPolicy</code>
|
|||
|
|
method.
|
|||
|
|
</span>
|
|||
|
|
|
|||
|
|
Note that you can set permanent message
|
|||
|
|
policies at any time during the life of the
|
|||
|
|
application.
|
|||
|
|
</p>
|
|||
|
|
<p>
|
|||
|
|
The following permanent message policies are available when you use
|
|||
|
|
the Replication Manager:
|
|||
|
|
</p>
|
|||
|
|
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
|
|||
|
|
<h3 class="title">Note</h3>
|
|||
|
|
<p>
|
|||
|
|
The following list mentions <span class="emphasis"><em>electable peer</em></span>
|
|||
|
|
several times. This is simply another environment that can be
|
|||
|
|
elected to be a master (that is, it has a priority greater than 0).
|
|||
|
|
Do not confuse this with the concept of a peer as used for client
|
|||
|
|
to client transfers. See <a class="xref" href="c2ctransfer.html" title="Client to Client Transfer">Client to Client Transfer</a> for more information on client
|
|||
|
|
to client transfers.
|
|||
|
|
</p>
|
|||
|
|
</div>
|
|||
|
|
<div class="itemizedlist">
|
|||
|
|
<ul type="disc">
|
|||
|
|
<li>
|
|||
|
|
<p>
|
|||
|
|
|
|||
|
|
<code class="literal">ReplicationManagerAckPolicy.NONE</code>
|
|||
|
|
</p>
|
|||
|
|
<p>
|
|||
|
|
No permanent message acknowledgments are required. If
|
|||
|
|
this policy is selected, permanent message handling is
|
|||
|
|
essentially "turned off." That is, the master will
|
|||
|
|
never wait for replica acknowledgments. In this case,
|
|||
|
|
transaction log data is either flushed or not strictly
|
|||
|
|
depending on the type of commit that is being performed
|
|||
|
|
(synchronous or asynchronous).
|
|||
|
|
</p>
|
|||
|
|
</li>
|
|||
|
|
<li>
|
|||
|
|
<p>
|
|||
|
|
|
|||
|
|
<code class="literal">ReplicationManagerAckPolicy.ONE</code>
|
|||
|
|
</p>
|
|||
|
|
<p>
|
|||
|
|
At least one replica must acknowledge the permanent
|
|||
|
|
message within the timeout period.
|
|||
|
|
</p>
|
|||
|
|
</li>
|
|||
|
|
<li>
|
|||
|
|
<p>
|
|||
|
|
|
|||
|
|
<code class="literal">ReplicationManagerAckPolicy.ONE_PEER</code>
|
|||
|
|
</p>
|
|||
|
|
<p>
|
|||
|
|
At least one electable peer must acknowledge the permanent
|
|||
|
|
message within the timeout period.
|
|||
|
|
</p>
|
|||
|
|
</li>
|
|||
|
|
<li>
|
|||
|
|
<p>
|
|||
|
|
|
|||
|
|
<code class="literal">ReplicationManagerAckPolicy.ALL</code>
|
|||
|
|
</p>
|
|||
|
|
<p>
|
|||
|
|
All replicas must acknowledge the message within
|
|||
|
|
the timeout period. This
|
|||
|
|
policy should be selected only if your replication
|
|||
|
|
group has a small number of replicas, and those replicas
|
|||
|
|
are on extremely reliable networks and servers.
|
|||
|
|
</p>
|
|||
|
|
</li>
|
|||
|
|
<li>
|
|||
|
|
<p>
|
|||
|
|
|
|||
|
|
<code class="literal">ReplicationManagerAckPolicy.ALL_AVAILABLE</code>
|
|||
|
|
</p>
|
|||
|
|
<p>
|
|||
|
|
All currently connected replication clients must
|
|||
|
|
acknowledge the message. This policy will invoke the
|
|||
|
|
<code class="literal">DB_EVENT_REP_PERM_FAILED</code> event if
|
|||
|
|
fewer than a quorum of clients acknowledged during that
|
|||
|
|
time.
|
|||
|
|
</p>
|
|||
|
|
</li>
|
|||
|
|
<li>
|
|||
|
|
<p>
|
|||
|
|
|
|||
|
|
<code class="literal">ReplicationManagerAckPolicy.ALL_PEERS</code>
|
|||
|
|
</p>
|
|||
|
|
<p>
|
|||
|
|
All electable peers must acknowledge the message within the
|
|||
|
|
timeout period. This
|
|||
|
|
policy should be selected only if your replication
|
|||
|
|
group is small, and its various environments
|
|||
|
|
are on extremely reliable networks and servers.
|
|||
|
|
</p>
|
|||
|
|
</li>
|
|||
|
|
<li>
|
|||
|
|
<p>
|
|||
|
|
|
|||
|
|
<code class="literal">ReplicationManagerAckPolicy.QUORUM</code>
|
|||
|
|
</p>
|
|||
|
|
<p>
|
|||
|
|
A quorum of electable peers must acknowledge the message within the timeout period.
|
|||
|
|
A quorum is reached when acknowledgments are received from the minimum number
|
|||
|
|
of environments needed to ensure that the record remains durable
|
|||
|
|
if an election is held. That is, the master wants to hear from enough
|
|||
|
|
electable replicas that they have committed the record so that if an election
|
|||
|
|
is held, the master knows the record will exist even if a new master is selected.
|
|||
|
|
</p>
|
|||
|
|
</li>
|
|||
|
|
</ul>
|
|||
|
|
</div>
|
|||
|
|
<p>
|
|||
|
|
By default, a quorum of electable peers must must acknowledge a permanent
|
|||
|
|
message in order for it considered to have been successfully
|
|||
|
|
transmitted.
|
|||
|
|
</p>
|
|||
|
|
</div>
|
|||
|
|
<div class="sect2" lang="en" xml:lang="en">
|
|||
|
|
<div class="titlepage">
|
|||
|
|
<div>
|
|||
|
|
<div>
|
|||
|
|
<h3 class="title"><a id="fmwrkpermtimeout"></a>Setting the Permanent Message Timeout</h3>
|
|||
|
|
</div>
|
|||
|
|
</div>
|
|||
|
|
</div>
|
|||
|
|
<p>
|
|||
|
|
The permanent message timeout represents the
|
|||
|
|
maximum amount of time the committing thread
|
|||
|
|
will block waiting for message
|
|||
|
|
acknowledgments. If sufficient
|
|||
|
|
acknowledgments arrive before this timeout has
|
|||
|
|
expired, the thread continues operations as
|
|||
|
|
normal. However, if this timeout expires, the
|
|||
|
|
committing thread flushes its transaction log
|
|||
|
|
buffer before continuing with normal
|
|||
|
|
operations.
|
|||
|
|
</p>
|
|||
|
|
<p>
|
|||
|
|
You set the timeout value using
|
|||
|
|
<code class="methodname">Environment.setReplicationTimeout()</code>.
|
|||
|
|
You pass this method the
|
|||
|
|
<code class="methodname">ReplicationTimeoutType.ACK_TIMEOUT</code>
|
|||
|
|
constant and a timeout value in microseconds.
|
|||
|
|
</p>
|
|||
|
|
<p>
|
|||
|
|
For example:
|
|||
|
|
</p>
|
|||
|
|
<pre class="programlisting"> dbenv.setReplicationTimeout(ReplicationTimeoutType.ACK_TIMEOUT, 100); </pre>
|
|||
|
|
<p>
|
|||
|
|
This timeout value can be set at anytime during the
|
|||
|
|
life of the application.
|
|||
|
|
</p>
|
|||
|
|
</div>
|
|||
|
|
<div class="sect2" lang="en" xml:lang="en">
|
|||
|
|
<div class="titlepage">
|
|||
|
|
<div>
|
|||
|
|
<div>
|
|||
|
|
<h3 class="title"><a id="perm2fmwrkexample"></a>Adding a Permanent Message Policy to
|
|||
|
|
|
|||
|
|
|
|||
|
|
<span>RepQuoteExampleGSG</span>
|
|||
|
|
</h3>
|
|||
|
|
</div>
|
|||
|
|
</div>
|
|||
|
|
</div>
|
|||
|
|
<p>
|
|||
|
|
For illustration purposes, we will now update
|
|||
|
|
|
|||
|
|
|
|||
|
|
<code class="literal">RepQuoteExampleGSG</code>
|
|||
|
|
such that it requires only one acknowledgment from
|
|||
|
|
a replica on transactional commits. Also, we will give
|
|||
|
|
this acknowledgment a 500 microsecond timeout
|
|||
|
|
value. This means that our application's main
|
|||
|
|
thread will block for up to 500 microseconds waiting
|
|||
|
|
for an acknowledgment. If it does not receive at
|
|||
|
|
least one acknowledgment in that amount of time,
|
|||
|
|
DB will flush the transaction logs to disk
|
|||
|
|
before continuing on.
|
|||
|
|
</p>
|
|||
|
|
<p>
|
|||
|
|
This is a very simple update. We can perform the
|
|||
|
|
entire thing in
|
|||
|
|
|
|||
|
|
<code class="methodname">RepQuoteExampleGSG.init()</code>
|
|||
|
|
immediately after we set the application's priority
|
|||
|
|
and before we open our environment handle.
|
|||
|
|
</p>
|
|||
|
|
<pre class="programlisting"> public int init(RepConfig config)
|
|||
|
|
throws DatabaseException
|
|||
|
|
{
|
|||
|
|
int ret = 0;
|
|||
|
|
repConfig = config;
|
|||
|
|
EnvironmentConfig envConfig = new EnvironmentConfig();
|
|||
|
|
envConfig.setErrorStream(System.err);
|
|||
|
|
envConfig.setErrorPrefix(RepConfig.progname);
|
|||
|
|
|
|||
|
|
envConfig.addReplicationManagerSite(repConfig.getThisHost());
|
|||
|
|
for (ReplicationHostAddress host =
|
|||
|
|
repConfig.getFirstOtherHost();
|
|||
|
|
host != null; host = repConfig.getNextOtherHost()){
|
|||
|
|
|
|||
|
|
ReplicationManagerSiteConfig repmgrRemoteSiteConfig =
|
|||
|
|
new ReplicationManagerSiteConfig(host.host, host.port);
|
|||
|
|
repmgrRemoteSiteConfig.setBootstrapHelper(true);
|
|||
|
|
envConfig.addReplicationManagerSite(
|
|||
|
|
repmgrRemoteSiteConfig);
|
|||
|
|
}
|
|||
|
|
envConfig.setReplicationPriority(appConfig.priority);
|
|||
|
|
|
|||
|
|
<strong class="userinput"><code>envConfig.setReplicationManagerAckPolicy(
|
|||
|
|
ReplicationManagerAckPolicy.ALL);
|
|||
|
|
envConfig.setReplicationTimeout(ReplicationTimeoutType.ACK_TIMEOUT,
|
|||
|
|
500); </code></strong>
|
|||
|
|
|
|||
|
|
envConfig.setCacheSize(RepConfig.CACHESIZE);
|
|||
|
|
envConfig.setTxnNoSync(true);
|
|||
|
|
... </pre>
|
|||
|
|
</div>
|
|||
|
|
</div>
|
|||
|
|
<div class="navfooter">
|
|||
|
|
<hr />
|
|||
|
|
<table width="100%" summary="Navigation footer">
|
|||
|
|
<tr>
|
|||
|
|
<td width="40%" align="left"><a accesskey="p" href="repmgr_init_example_c.html">Prev</a> </td>
|
|||
|
|
<td width="20%" align="center">
|
|||
|
|
<a accesskey="u" href="repapp.html">Up</a>
|
|||
|
|
</td>
|
|||
|
|
<td width="40%" align="right"> <a accesskey="n" href="electiontimes.html">Next</a></td>
|
|||
|
|
</tr>
|
|||
|
|
<tr>
|
|||
|
|
<td width="40%" align="left" valign="top">Adding the Replication Manager to
|
|||
|
|
|
|||
|
|
|
|||
|
|
<span>SimpleTxn</span>
|
|||
|
|
</td>
|
|||
|
|
<td width="20%" align="center">
|
|||
|
|
<a accesskey="h" href="index.html">Home</a>
|
|||
|
|
</td>
|
|||
|
|
<td width="40%" align="right" valign="top"> Managing Election Times</td>
|
|||
|
|
</tr>
|
|||
|
|
</table>
|
|||
|
|
</div>
|
|||
|
|
</body>
|
|||
|
|
</html>
|