Import BSDDB 4.7.25 (as of svn r89086)
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Zachary Ware
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docs/gsg_txn/JAVA/reversesplit.html
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docs/gsg_txn/JAVA/reversesplit.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>Reverse BTree Splits</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 V1.62.4" />
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<link rel="home" href="index.html" title="Getting Started with Berkeley DB Transaction Processing" />
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<link rel="up" href="txnconcurrency.html" title="Chapter 4. Concurrency" />
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<link rel="previous" href="txnnowait.html" title="No Wait on Blocks" />
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<link rel="next" href="filemanagement.html" title="Chapter 5. Managing DB Files" />
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</head>
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<body>
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<div class="navheader">
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">Reverse BTree Splits</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="txnnowait.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 4. Concurrency</th>
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<td width="20%" align="right"> <a accesskey="n" href="filemanagement.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="reversesplit"></a>Reverse BTree Splits</h2>
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</div>
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</div>
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<div></div>
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</div>
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<p>
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If your application is using the Btree access method, and your
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application is repeatedly deleting then adding records to your
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database, then you might be able to reduce lock contention by
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turning off reverse Btree splits.
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</p>
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<p>
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As pages are emptied in a database, DB attempts to
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delete empty pages in order to keep
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the database as small as possible and minimize search time.
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Moreover, when a page in the database fills
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up, DB, of course, adds additional pages
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to make room for more data.
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</p>
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<p>
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Adding and deleting pages in the database requires that the
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writing thread lock the parent page. Consequently, as the
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number of pages in your database diminishes, your application
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will see increasingly more lock contention; the maximum level
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of concurrency in a database of two pages is far smaller than
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that in a database of 100 pages, because there are fewer pages
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that can be locked.
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</p>
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<p>
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Therefore, if you prevent the database from being reduced to a
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minimum number of pages, you can improve your application's
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concurrency throughput. Note, however, that you should do so
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only if your application tends to delete and then add the same
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data. If this is not the case, then preventing reverse Btree
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splits can harm your database search time.
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</p>
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<p>
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To turn off reverse Btree splits,
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<span>
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set
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<tt class="methodname">DatabaseConfig.setReverseSplitOff()</tt>.
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to <tt class="literal">true</tt>.
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</span>
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</p>
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<p>
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For example:
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</p>
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<pre class="programlisting">package db.txn;
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import com.sleepycat.db.Database;
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import com.sleepycat.db.DatabaseType;
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import com.sleepycat.db.DatabaseConfig;
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import com.sleepycat.db.DatabaseException;
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import com.sleepycat.db.Environment;
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import com.sleepycat.db.EnvironmentConfig;
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import java.io.File;
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import java.io.FileNotFoundException;
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...
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Database myDatabase = null;
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Environment myEnv = null;
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try {
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EnvironmentConfig myEnvConfig = new EnvironmentConfig();
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myEnvConfig.setInitializeCache(true);
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myEnvConfig.setInitializeLocking(true);
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myEnvConfig.setInitializeLogging(true);
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myEnvConfig.setTransactional(true);
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myEnv = new Environment(new File("/my/env/home"),
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myEnvConfig);
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// Open the database.
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DatabaseConfig dbConfig = new DatabaseConfig();
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dbConfig.setTransactional(true);
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dbConfig.setType(DatabaseType.BTREE);
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// Set BTree reverse split to off
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dbConfig.setReverseSplitOff(true);
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myDatabase = myEnv.openDatabase(null, // txn handle
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"sampleDatabase", // db file name
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"null", // db name
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dbConfig);
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} catch (DatabaseException de) {
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// Exception handling goes here
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} catch (FileNotFoundException fnfe) {
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// Exception handling goes here
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}</pre>
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<p>
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Or, if you are using the DPL:
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</p>
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<pre class="programlisting">package db.txn;
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import com.sleepycat.db.Database;
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import com.sleepycat.db.DatabaseType;
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import com.sleepycat.db.DatabaseConfig;
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import com.sleepycat.db.DatabaseException;
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import com.sleepycat.db.Environment;
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import com.sleepycat.db.EnvironmentConfig;
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import java.io.File;
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import java.io.FileNotFoundException;
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...
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EntityStore myStore = null;
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Environment myEnv = null;
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try {
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EnvironmentConfig myEnvConfig = new EnvironmentConfig();
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myEnvConfig.setInitializeCache(true);
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myEnvConfig.setInitializeLocking(true);
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myEnvConfig.setInitializeLogging(true);
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myEnvConfig.setTransactional(true);
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myEnv = new Environment(new File("/my/env/home"),
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myEnvConfig);
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// Configure the store.
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StoreConfig myStoreConfig = new StoreConfig();
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myStoreConfig.setAllowCreate(true);
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myStoreConfig.setTransactional(true);
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// Configure the underlying database.
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DatabaseConfig dbConfig = new DatabaseConfig();
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dbConfig.setTransactional(true);
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dbConfig.setAllowCreate(true);
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dbConfig.setType(DatabaseType.BTREE);
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// Set BTree reverse split to off
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dbConfig.setReverseSplitOff(true);
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// Instantiate the store
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myStore = new EntityStore(myEnv, "store_name", myStoreConfig);
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// Set the DatabaseConfig object, so that the underlying
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// database is configured for uncommitted reads.
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myStore.setPrimaryConfig(SomeEntityClass.class, dbConfig);
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} catch (DatabaseException de) {
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// Exception handling goes here
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} catch (FileNotFoundException fnfe) {
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// Exception handling goes here
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}</pre>
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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="txnnowait.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="txnconcurrency.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="filemanagement.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">No Wait on Blocks </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 5. Managing DB Files</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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