1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
|
<?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>Adding the Replication Manager to ex_rep_gsg_simple</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="rep_init_code.html" title="Starting and Stopping Replication" />
<link rel="next" href="fwrkpermmessage.html" title="Permanent Message Handling" />
</head>
<body>
<div xmlns="" class="navheader">
<div class="libver">
<p>Library Version 11.2.5.3</p>
</div>
<table width="100%" summary="Navigation header">
<tr>
<th colspan="3" align="center">Adding the Replication Manager to
<span xmlns="http://www.w3.org/1999/xhtml">ex_rep_gsg_simple</span>
</th>
</tr>
<tr>
<td width="20%" align="left"><a accesskey="p" href="rep_init_code.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="fwrkpermmessage.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="repmgr_init_example_c"></a>Adding the Replication Manager to
<span>ex_rep_gsg_simple</span>
</h2>
</div>
</div>
</div>
<p>
We now use the methods described above to add partial
support to the
<span>ex_rep_gsg_simple</span>
example that we presented in
<a class="xref" href="txnapp.html" title="Chapter 2. Transactional Application">Transactional Application</a>.
That is, in this section we will:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
Enhance our command line options to accept information
of interest to a replicated application.
</p>
</li>
<li>
<p>
Configure our environment handle to use replication and
the Replication Manager.
</p>
</li>
<li>
<p>
Minimally configure the Replication Manager.
</p>
</li>
<li>
<p>
Start replication.
</p>
</li>
</ul>
</div>
<p>
Note that when we are done with this section, we will be
only partially ready to run the application. Some critical
pieces will be missing; specifically, we will not yet be
handling the differences between a master and a
replica. (We do that in the next chapter).
</p>
<p>
Also, note that in the following code fragments, additions
and changes to the code are marked in <strong class="userinput"><code>bold</code></strong>.
</p>
<p>
To begin, we copy the
<span>ex_rep_gsg_simple</span>
code to a new file called
<code class="literal">ex_rep_gsg_repmgr.c</code>.
<span>
We then make the corresponding change to the program name.
</span>
</p>
<pre class="programlisting">/*
<strong class="userinput"><code>* File: ex_rep_gsg_repmgr.c</code></strong>
*/
#include <stdlib.h>
#include <string.h>
#ifndef _WIN32
#include <unistd.h>
#endif
#include <db.h>
#ifdef _WIN32
extern int getopt(int, char * const *, const char *);
#endif
#define CACHESIZE (10 * 1024 * 1024)
#define DATABASE "quote.db"
const char *progname = <strong class="userinput"><code>"ex_rep_gsg_repmgr";</code></strong>
int create_env(const char *, DB_ENV **);
int env_init(DB_ENV *, const char *);
int doloop (DB_ENV *);
int print_stocks(DBC *); </pre>
<p>
Next we update our usage function. The application will continue to
accept the <code class="literal">-h</code> parameter so that we can identify
the environment home directory used by this application. However,
we also add the:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
<code class="literal">-l</code> parameter which allows us to identify the
host and port used by this application to listen for
replication messages. This parameter is required unless the -L
parameter is specified.
</p>
</li>
<li>
<p>
<code class="literal">-L</code> parameter, which allows us to identify
the local site as the group creator.
</p>
</li>
<li>
<p>
<code class="literal">-r</code> parameter which allows us to specify
other replicas.
</p>
</li>
<li>
<p>
<code class="literal">-p</code> option, which is used to identify this
replica's priority (recall that the priority is used as a tie
breaker for elections)
</p>
</li>
</ul>
</div>
<pre class="programlisting">/* Usage function */
static void
usage()
{
fprintf(stderr, "usage: %s ", progname);
fprintf(stderr, "-h home <strong class="userinput"><code>-l|-L host:port</code></strong>\n");
<strong class="userinput"><code>fprintf(stderr, "\t\t[-r host:port][-p priority]\n");
fprintf(stderr, "where:\n");
fprintf(stderr, "\t-h identifies the environment home directory ");
fprintf(stderr, "(required).\n");
fprintf(stderr, "\t-l identifies the host and port used by this ");
fprintf(stderr, "site (required, unless -L is specified).\n");
fprintf(stderr, "\t-L identifies the host and port used by this ");
fprintf(stderr, "site, which is the group creator.\n");
fprintf(stderr, "\t-r identifies another site participating in ");
fprintf(stderr, "this replication group\n");
fprintf(stderr, "\t-p identifies the election priority used by ");
fprintf(stderr, "this replica.\n");</code></strong>
exit(EXIT_FAILURE);
} </pre>
<p>
Now we can begin working on our <code class="literal">main()</code> function.
We begin by adding a couple of variables that we will use to
collect TCP/IP host and port information.
<span>
We also declare a couple
of flags that we use to make sure some required information is
provided to this application.
</span>
</p>
<pre class="programlisting">int
main(int argc, char *argv[])
{
DB_ENV *dbenv;
<strong class="userinput"><code>DB_SITE *dbsite;</code></strong>
extern char *optarg;
const char *home;
char ch, <strong class="userinput"><code>*host, *portstr</code></strong>;
int ret, <strong class="userinput"><code>local_is_set, is_group_creator</code></strong>;
<strong class="userinput"><code>u_int32_t port</code></strong>;
dbenv = NULL;
ret = <strong class="userinput"><code>local_is_set = is_group_creator = </code></strong>0;
home = NULL; </pre>
<p>
At this time we can create our environment handle and configure it
exactly as we did for <code class="literal">simple_txn</code>.
The only thing that we will do differently here is that we will set a priority,
arbitrarily picked to be 100, so that we can be sure the environment has
a priority other than 0 (the default value). This ensures that the
environment can become a master via an election.
</p>
<pre class="programlisting"> if ((ret = create_env(progname, &dbenv)) != 0)
goto err;
/* Default priority is 100 */
<strong class="userinput"><code>dbenv->rep_set_priority(dbenv, 100);</code></strong> </pre>
<p>
Now we collect our command line arguments. As we do so, we will
configure host and port information as required, and we will
configure the application's election priority if necessary.
</p>
<pre class="programlisting"> /* Collect the command line options */
while ((ch = getopt(argc, argv, "h:<strong class="userinput"><code>l:L:p:r:</code></strong>")) != EOF)
switch (ch) {
case 'h':
home = optarg;
break;
<strong class="userinput"><code>/* Set the host and port used by this environment */
case 'l':
host = strtok(optarg, ":");
if ((portstr = strtok(NULL, ":")) == NULL) {
fprintf(stderr, "Bad host specification.\n");
goto err;
}
port = (unsigned short)atoi(portstr);
if ((ret = dbenv->repmgr_site(dbenv, host, port, &dbsite
0)) != 0 ) {
fprintf(stderr,
"Could not set local address %s.\n", host);
goto err;
}
dbsite->set_config(dbsite, DB_LOCAL_SITE, 1);
if (is_group_creator)
dbsite->set_config(dbsite, DB_GROUP_CREATOR, 1);
if ((ret = dbsite->close(dbsite)) != 0) {
dbenv->(dbenv, ret, "DB_SITE->close");
goto err;
}
local_is_set = 1;
break;
/* Set this replica's election priority */
case 'p':
dbenv->rep_set_priority(dbenv, atoi(optarg));
break;
/* Identify another site in the replication group */
case 'r':
host = strtok(optarg, ":");
if ((portstr = strtok(NULL, ":")) == NULL) {
fprintf(stderr, "Bad host specification.\n");
goto err;
}
port = (unsigned short)atoi(portstr);
if ((dbenv->repmgr_site(dbenv, host, port, &dbsite,
0)) != 0) {
fprintf(stderr,
"Could not add site %s.\n", host);
goto err;
}
dbenv->set_config(dbsite, DB_BOOTSTRAP_HELPER, 1);
if ((dbenv->close(dbsite)) != 0) {
dbenv->err(dbenv, ret, "DB_SITE->close");
goto err;
}
break;</code></strong>
case '?':
default:
usage();
}
/* Error check command line. */
if (home == NULL <strong class="userinput"><code>|| !local_is_set</code></strong>)
usage(); </pre>
<p>
Having done that, we can call <code class="function">env_init()</code>,
which we use to open our environment handle. Note that this
function changes slightly for this update (see below).
</p>
<pre class="programlisting"> if ((ret = env_init(dbenv, home)) != 0)
goto err; </pre>
<p>
Finally, we start replication before we go into the
<code class="function">doloop()</code> function (where we perform all our
database access).
</p>
<pre class="programlisting">
<strong class="userinput"><code>if ((ret = dbenv->repmgr_start(dbenv, 3, DB_REP_ELECTION)) != 0)
goto err; </code></strong>
if ((ret = doloop(dbenv)) != 0) {
dbenv->err(dbenv, ret, "Application failed");
goto err;
}
err: if (dbenv != NULL)
(void)dbenv->close(dbenv, 0);
return (ret);
} </pre>
<p>
<span>Beyond that, the rest of our application remains the same for
now, with the exception of the <code class="function">env_init()</code>
function, which we use to actually open our environment handle.
The flags </span>
we use to open the environment are slightly different for a
replicated application than they are for a non-replicated
application. Namely, replication requires the
<span>
<code class="literal">DB_INIT_REP</code> flag.
</span>
</p>
<p>
Also, because we are using the Replication Manager, we must prepare
our environment for threaded usage. For this reason, we also
need the <code class="literal">DB_THREAD</code> flag.
</p>
<pre class="programlisting">int
env_init(DB_ENV *dbenv, const char *home)
{
u_int32_t flags;
int ret;
(void)dbenv->set_cachesize(dbenv, 0, CACHESIZE, 0);
(void)dbenv->set_flags(dbenv, DB_TXN_NOSYNC, 1);
flags = DB_CREATE |
DB_INIT_LOCK |
DB_INIT_LOG |
DB_INIT_MPOOL |
<strong class="userinput"><code>DB_INIT_REP |</code></strong>
DB_INIT_TXN |
DB_RECOVER <strong class="userinput"><code>|
DB_THREAD;</code></strong>
if ((ret = dbenv->open(dbenv, home, flags, 0)) != 0)
dbenv->err(dbenv, ret, "can't open environment");
return (ret);
}</pre>
<p>
This completes our replication updates for the moment. We are not as
yet ready to actually run this program; there remains a few
critical pieces left to add to it. However, the work that we
performed in this section represents a solid foundation for the
remainder of our replication work.
</p>
</div>
<div class="navfooter">
<hr />
<table width="100%" summary="Navigation footer">
<tr>
<td width="40%" align="left"><a accesskey="p" href="rep_init_code.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="fwrkpermmessage.html">Next</a></td>
</tr>
<tr>
<td width="40%" align="left" valign="top">
Starting and Stopping Replication
</td>
<td width="20%" align="center">
<a accesskey="h" href="index.html">Home</a>
</td>
<td width="40%" align="right" valign="top"> Permanent Message Handling</td>
</tr>
</table>
</div>
</body>
</html>
|
