2013-11-12 19:50:46 +01:00
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2013-11-15 02:32:57 +01:00
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2013-11-12 19:50:46 +01:00
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<meta charset='utf-8'>
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<title>RocksDB | A persistent key-value store for fast storage environments</title>
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<meta property='og:title' content='RocksDB | A persistent key-value store for fast storage environments'>
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<meta property='og:description' content='A persistent key-value store for fast storage environments'>
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2013-11-13 00:13:32 +01:00
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2013-11-12 19:50:46 +01:00
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</head>
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<body>
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<header class='topbar'><nav class='width'>
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<a href='index.html'><h1>RocksDB</h1></a>
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<ul>
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<li><a href='overview.html' class='active'>Overview</a></li>
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<li><a href='https://github.com/facebook/rocksdb/wiki/_pages'>Wiki</a></li>
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<li><a href='https://github.com/facebook/rocksdb'>GitHub</a>
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</ul>
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</nav></header>
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<header class='hero'><div class='width'>
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<hgroup>
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<h1>
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Overview
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</h1>
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</hgroup>
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</div></header>
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<section class='content'><div class='width'>
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<article>
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2013-11-14 05:40:05 +01:00
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<p> The <code>rocksdb</code> library provides a persistent key value store. Keys
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and values are arbitrary byte arrays. The keys are ordered within the key value
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store according to a user-specified comparator function. </p>
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<p> The library is maintained by the Facebook Database Engineering Team, and is
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based on leveldb, by Sanjay Ghemawat and Jeff Dean at Google. </p>
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<h2>Opening A Database</h2>
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<p> A <code>rocksdb</code> database has a name which corresponds to a file
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system directory. All of the contents of database are stored in this directory.
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The following example shows how to open a database, creating it if necessary:
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</p>
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<pre>#include <assert>
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#include "rocksdb/db.h"
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rocksdb::DB* db;
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rocksdb::Options options;
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options.create_if_missing = true;
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rocksdb::Status status =
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rocksdb::DB::Open(options, "/tmp/testdb", &db);
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assert(status.ok());
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...</pre>
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2013-11-14 05:40:05 +01:00
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<p>
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If you want to raise an error if the database already exists, add the following
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line before the <code>rocksdb::DB::Open</code> call:
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</p>
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<pre>options.error_if_exists = true;</pre>
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2013-11-14 05:40:05 +01:00
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<h2>Status</h2>
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<p>
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You may have noticed the <code>rocksdb::Status</code> type above. Values of this
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type are returned by most functions in <code>rocksdb</code> that may encounter
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an error. You can check if such a result is ok, and also print an associated
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error message:
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</p>
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<pre>rocksdb::Status s = ...;
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if (!s.ok()) cerr << s.ToString() << endl;</pre>
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<h2>Closing A Database</h2>
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<p>
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When you are done with a database, just delete the database object. For example:
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</p>
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<pre>/* open the db as described above */
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/* do something with db */
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delete db;</pre>
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<h2>Reads And Writes</h2>
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<p>
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The database provides <code>Put</code>, <code>Delete</code>, and
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<code>Get</code> methods to modify/query the database. For example, the
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following code moves the value stored under <code>key1</code> to
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<code>key2</code>.
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</p>
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<pre>std::string value;
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rocksdb::Status s = db->Get(rocksdb::ReadOptions(), key1, &value);
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if (s.ok()) s = db->Put(rocksdb::WriteOptions(), key2, value);
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if (s.ok()) s = db->Delete(rocksdb::WriteOptions(), key1);</pre>
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<h2>Further documentation</h2>
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<p>
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These are just simple examples of how RocksDB is used. The full documentation is
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available within the
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<a href='https://github.com/facebook/rocksdb/blob/master/doc/'><code>/doc</code></a>
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folder of the project.
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</p>
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<p>
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In addition, further details about the RocksDB implementation may be found in
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the following documents:
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</p>
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<ul>
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<li><a href='https://github.com/facebook/rocksdb/wiki/_pages'>
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RocksDB Project Wiki</a></li>
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<li><a href='https://github.com/facebook/rocksdb/wiki/Rocksdb-Architecture-Guide'>
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Architecture Guide</a></li>
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<li><a href='https://github.com/facebook/rocksdb/wiki/Rocksdb-Table-Format'>
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Format of an immutable Table file</a></li>
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<li> <a href='https://github.com/facebook/rocksdb/blob/master/doc/log_format.txt'>
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Format of a log file</a></li>
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</ul>
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2013-11-12 19:50:46 +01:00
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</article>
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</div></section>
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© Copyright 2013, Facebook
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