1<?xml version="1.0" encoding="UTF-8" standalone="no"?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml"> 4 <head> 5 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> 6 <title>Chapter��5.��Managing DB Files</title> 7 <link rel="stylesheet" href="gettingStarted.css" type="text/css" /> 8 <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /> 9 <link rel="start" href="index.html" title="Getting Started with Berkeley DB Transaction Processing" /> 10 <link rel="up" href="index.html" title="Getting Started with Berkeley DB Transaction Processing" /> 11 <link rel="prev" href="reversesplit.html" title="Reverse BTree Splits" /> 12 <link rel="next" href="backuprestore.html" title="Backup Procedures" /> 13 </head> 14 <body> 15 <div class="navheader"> 16 <table width="100%" summary="Navigation header"> 17 <tr> 18 <th colspan="3" align="center">Chapter��5.��Managing DB Files</th> 19 </tr> 20 <tr> 21 <td width="20%" align="left"><a accesskey="p" href="reversesplit.html">Prev</a>��</td> 22 <th width="60%" align="center">��</th> 23 <td width="20%" align="right">��<a accesskey="n" href="backuprestore.html">Next</a></td> 24 </tr> 25 </table> 26 <hr /> 27 </div> 28 <div class="chapter" lang="en" xml:lang="en"> 29 <div class="titlepage"> 30 <div> 31 <div> 32 <h2 class="title"><a id="filemanagement"></a>Chapter��5.��Managing DB Files</h2> 33 </div> 34 </div> 35 </div> 36 <div class="toc"> 37 <p> 38 <b>Table of Contents</b> 39 </p> 40 <dl> 41 <dt> 42 <span class="sect1"> 43 <a href="filemanagement.html#checkpoints">Checkpoints</a> 44 </span> 45 </dt> 46 <dt> 47 <span class="sect1"> 48 <a href="backuprestore.html">Backup Procedures</a> 49 </span> 50 </dt> 51 <dd> 52 <dl> 53 <dt> 54 <span class="sect2"> 55 <a href="backuprestore.html#copyutilities">About Unix Copy Utilities</a> 56 </span> 57 </dt> 58 <dt> 59 <span class="sect2"> 60 <a href="backuprestore.html#standardbackup">Offline Backups</a> 61 </span> 62 </dt> 63 <dt> 64 <span class="sect2"> 65 <a href="backuprestore.html#hotbackup">Hot Backup</a> 66 </span> 67 </dt> 68 <dt> 69 <span class="sect2"> 70 <a href="backuprestore.html#incrementalbackups">Incremental Backups</a> 71 </span> 72 </dt> 73 </dl> 74 </dd> 75 <dt> 76 <span class="sect1"> 77 <a href="recovery.html">Recovery Procedures</a> 78 </span> 79 </dt> 80 <dd> 81 <dl> 82 <dt> 83 <span class="sect2"> 84 <a href="recovery.html#normalrecovery">Normal Recovery</a> 85 </span> 86 </dt> 87 <dt> 88 <span class="sect2"> 89 <a href="recovery.html#catastrophicrecovery">Catastrophic Recovery</a> 90 </span> 91 </dt> 92 </dl> 93 </dd> 94 <dt> 95 <span class="sect1"> 96 <a href="architectrecovery.html">Designing Your Application for Recovery</a> 97 </span> 98 </dt> 99 <dd> 100 <dl> 101 <dt> 102 <span class="sect2"> 103 <a href="architectrecovery.html#multithreadrecovery">Recovery for Multi-Threaded Applications</a> 104 </span> 105 </dt> 106 <dt> 107 <span class="sect2"> 108 <a href="architectrecovery.html#multiprocessrecovery">Recovery in Multi-Process Applications</a> 109 </span> 110 </dt> 111 </dl> 112 </dd> 113 <dt> 114 <span class="sect1"> 115 <a href="hotfailover.html">Using Hot Failovers</a> 116 </span> 117 </dt> 118 <dt> 119 <span class="sect1"> 120 <a href="logfileremoval.html">Removing Log Files</a> 121 </span> 122 </dt> 123 <dt> 124 <span class="sect1"> 125 <a href="logconfig.html">Configuring the Logging Subsystem</a> 126 </span> 127 </dt> 128 <dd> 129 <dl> 130 <dt> 131 <span class="sect2"> 132 <a href="logconfig.html#logfilesize">Setting the Log File Size</a> 133 </span> 134 </dt> 135 <dt> 136 <span class="sect2"> 137 <a href="logconfig.html#logregionsize">Configuring the Logging Region Size</a> 138 </span> 139 </dt> 140 <dt> 141 <span class="sect2"> 142 <a href="logconfig.html#inmemorylogging">Configuring In-Memory Logging</a> 143 </span> 144 </dt> 145 <dt> 146 <span class="sect2"> 147 <a href="logconfig.html#logbuffer">Setting the In-Memory Log Buffer Size</a> 148 </span> 149 </dt> 150 </dl> 151 </dd> 152 </dl> 153 </div> 154 <p> 155 DB is capable of storing several types of files on disk: 156 </p> 157 <div class="itemizedlist"> 158 <ul type="disc"> 159 <li> 160 <p> 161 Data files, which contain the actual data in your database. 162 </p> 163 </li> 164 <li> 165 <p> 166 Log files, which contain information required to recover your 167 database in the event of a system or application failure. 168 </p> 169 </li> 170 <li> 171 <p> 172 Region files, which contain information necessary for the 173 overall operation of your application. 174 </p> 175 </li> 176 <li> 177 <p> 178 Temporary files, which are created only under certain special circumstances. These files never need to 179 be backed up or otherwise managed and so they are not a consideration for the topics described in this 180 chapter. See <a class="xref" href="enabletxn.html#security" title="Security Considerations">Security Considerations</a> 181 for more information on temporary files. 182 </p> 183 </li> 184 </ul> 185 </div> 186 <p> 187 Of these, you must manage your data and log files by ensuring that they 188 are backed up. You should also pay attention to the amount of disk space 189 your log files are consuming, and periodically remove any unneeded 190 files. Finally, you can optionally tune your logging subsystem to best 191 suit your application's needs and requirements. 192 These topics are discussed in this chapter. 193 </p> 194 <div class="sect1" lang="en" xml:lang="en"> 195 <div class="titlepage"> 196 <div> 197 <div> 198 <h2 class="title" style="clear: both"><a id="checkpoints"></a>Checkpoints</h2> 199 </div> 200 </div> 201 </div> 202 <p> 203 Before we can discuss DB file management, we need to 204 describe checkpoints. When databases are modified (that is, a 205 transaction is committed), the modifications are recorded in 206 DB's logs, but they are <span class="emphasis"><em>not</em></span> 207 necessarily reflected in the actual database files on disk. 208 </p> 209 <p> 210 This means that as time goes on, increasingly 211 more data is contained in your log files that is not 212 contained in your data files. As a result, you must keep more 213 log files around than you might actually need. Also, any 214 recovery run from your log files will take increasingly longer 215 amounts of time, because there is more data in the log files 216 that must be reflected back into the data files during the 217 recovery process. 218 </p> 219 <p> 220 You can reduce these problems by periodically 221 running a checkpoint against your environment. The checkpoint: 222 </p> 223 <div class="itemizedlist"> 224 <ul type="disc"> 225 <li> 226 <p> 227 Flushes dirty pages from the in-memory cache. This means that data modifications found in your 228 in-memory cache are written to the database files on disk. Note that a checkpoint also causes data 229 dirtied by an uncommitted transaction to also be written to your database files on disk. In this latter 230 case, DB's normal recovery is used to remove any such modifications that were subsequently 231 abandoned by your application using a transaction abort. 232 </p> 233 <p> 234 Normal recovery is describe in <a class="xref" href="recovery.html" title="Recovery Procedures">Recovery Procedures</a>. 235 </p> 236 </li> 237 <li> 238 <p> 239 Writes a checkpoint record. 240 </p> 241 </li> 242 <li> 243 <p> 244 Flushes the log. This causes all log data that has not yet been written to disk to be written. 245 </p> 246 </li> 247 <li> 248 <p> 249 Writes a list of open databases. 250 </p> 251 </li> 252 </ul> 253 </div> 254 <p> 255 There are several ways to run a checkpoint. One way is to use 256 the <span class="command"><strong>db_checkpoint</strong></span> command line utility. (Note, however, that this command line utility 257 cannot be used if your environment was opened using 258 259 <span> 260 <code class="methodname">EnvironmentConfig.setPrivate()</code>.) 261 </span> 262 </p> 263 <p> 264 You can also run a thread that periodically checkpoints your 265 environment for you by calling the 266 267 268 <code class="methodname">Environment.checkpoint()</code> 269 method. 270 </p> 271 <p> 272 Note that you can prevent a checkpoint from occurring unless more 273 than a specified amount of log data has been written since the 274 last checkpoint. You can also prevent the checkpoint from 275 running unless more than a specified amount of time has 276 occurred since the last checkpoint. These conditions are 277 particularly interesting if you have multiple threads 278 <span>or processes</span> 279 running checkpoints. 280 </p> 281 <p> 282 For configuration information, see the 283 284 285 <a class="ulink" href="http://www.oracle.com/technology/documentation/berkeley-db/db/java/com/sleepycat/db/CheckpointConfig.html" target="_top"> 286 CheckpointConfig Javadoc page. 287 </a> 288 </p> 289 <p> 290 Note that running checkpoints can be quite expensive. DB must 291 flush every dirty page to the backing database files. On the 292 other hand, if you do not run checkpoints often enough, your 293 recovery time can be unnecessarily long and you may be using more 294 disk space than you really need. Also, you cannot remove log files 295 until a checkpoint is run. Therefore, deciding how frequently 296 to run a checkpoint is one of the most 297 common tuning activity for DB applications. 298 </p> 299 <p> 300 For example, the following class performs a checkpoint every 60 seconds, so long as 500 kb of logging data has been 301 written since the last checkpoint: 302</p> 303 <pre class="programlisting"><span>package db.txn;</span> 304 305import com.sleepycat.db.CheckpointConfig; 306import com.sleepycat.db.DatabaseException; 307import com.sleepycat.db.Environment; 308 309public class CheckPointer extends Thread 310{ 311 private CheckpointConfig cpc = new CheckpointConfig(); 312 private Environment myEnv = null; 313 private static boolean canRun = true; 314 315 316 // Constructor. 317 CheckPointer(Environment env) { 318 myEnv = env; 319 // Run a checkpoint only if 500 kbytes of log data has been 320 // written. 321 cpc.setKBytes(500); 322 } 323 324 // Thread method that performs a checkpoint every 325 // 60 seconds 326 public void run () { 327 while (canRun) { 328 try { 329 myEnv.checkpoint(cpc); 330 sleep(60000); 331 } catch (DatabaseException de) { 332 System.err.println("Checkpoint error: " + 333 de.toString()); 334 } catch (InterruptedException e) { 335 // Should never get here 336 System.err.println("got interrupted exception"); 337 } 338 } 339 } 340 341 public static void stopRunning() { 342 canRun = false; 343 } 344} </pre> 345 <p> 346 And you use this class as follows. Note that we add the call to shutdown the checkpoint thread in our application's 347 shutdown code: 348</p> 349 <pre class="programlisting">package db.txn; 350 351import com.sleepycat.db.DatabaseException; 352import com.sleepycat.db.Environment; 353import com.sleepycat.db.EnvironmentConfig; 354 355import java.io.File; 356import java.io.FileNotFoundException; 357 358 359public class TryCheckPoint { 360 361 private static String myEnvPath = "./"; 362 363 private static Environment myEnv = null; 364 365 366 private static void usage() { 367 System.out.println("TxnGuide [-h <env directory>]"); 368 System.exit(-1); 369 } 370 371 public static void main(String args[]) { 372 try { 373 // Parse the arguments list 374 parseArgs(args); 375 // Open the environment and databases 376 openEnv(); 377 378 // Start the checkpoint thread 379 CheckPointer cp = new CheckPointer(myEnv); 380 cp.start(); 381 382 ////////////////////////////////// 383 // Do database work here as normal 384 ////////////////////////////////// 385 386 // Once all database work is completed, stop the checkpoint 387 // thread. 388 CheckPointer.stopRunning(); 389 390 // Join the checkpoint thread in case it needs some time to 391 // cleanly shutdown. 392 cp.join(); 393 394 } catch (Exception e) { 395 System.err.println("TryCheckPoint: " + e.toString()); 396 e.printStackTrace(); 397 } finally { 398 closeEnv(); 399 } 400 System.out.println("All done."); 401 } 402 403 // Open an environment and databases 404 private static void openEnv() throws DatabaseException { 405 System.out.println("opening env"); 406 407 // Set up the environment. 408 EnvironmentConfig myEnvConfig = new EnvironmentConfig(); 409 myEnvConfig.setAllowCreate(true); 410 myEnvConfig.setInitializeCache(true); 411 myEnvConfig.setInitializeLocking(true); 412 myEnvConfig.setInitializeLogging(true); 413 myEnvConfig.setTransactional(true); 414 // EnvironmentConfig.setThreaded(true) is the default behavior 415 // in Java, so we do not have to do anything to cause the 416 // environment handle to be free-threaded. 417 418 try { 419 // Open the environment 420 myEnv = new Environment(new File(myEnvPath), // Env home 421 myEnvConfig); 422 423 // Skipping the database opens and closes for brevity 424 425 } catch (FileNotFoundException fnfe) { 426 System.err.println("openEnv: " + fnfe.toString()); 427 System.exit(-1); 428 } 429 } 430 431 // Close the environment and databases 432 private static void closeEnv() { 433 System.out.println("Closing env"); 434 if (myEnv != null ) { 435 try { 436 myEnv.close(); 437 } catch (DatabaseException e) { 438 System.err.println("closeEnv: " + e.toString()); 439 e.printStackTrace(); 440 } 441 } 442 } 443 444 private TryCheckPoint() {} 445 446 private static void parseArgs(String args[]) { 447 for(int i = 0; i < args.length; ++i) { 448 if (args[i].startsWith("-")) { 449 switch(args[i].charAt(1)) { 450 case 'h': 451 myEnvPath = new String(args[++i]); 452 break; 453 default: 454 usage(); 455 } 456 } 457 } 458 } 459} </pre> 460 </div> 461 </div> 462 <div class="navfooter"> 463 <hr /> 464 <table width="100%" summary="Navigation footer"> 465 <tr> 466 <td width="40%" align="left"><a accesskey="p" href="reversesplit.html">Prev</a>��</td> 467 <td width="20%" align="center">��</td> 468 <td width="40%" align="right">��<a accesskey="n" href="backuprestore.html">Next</a></td> 469 </tr> 470 <tr> 471 <td width="40%" align="left" valign="top">Reverse BTree Splits��</td> 472 <td width="20%" align="center"> 473 <a accesskey="h" href="index.html">Home</a> 474 </td> 475 <td width="40%" align="right" valign="top">��Backup Procedures</td> 476 </tr> 477 </table> 478 </div> 479 </body> 480</html> 481