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79 lines
2.8 KiB
79 lines
2.8 KiB
1 year ago
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---
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docid: getting-started
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title: Getting started
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layout: docs
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permalink: /docs/getting-started.html
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---
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## Overview
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The RocksDB library provides a persistent key value store. Keys and values are arbitrary byte arrays. The keys are ordered within the key value store according to a user-specified comparator function.
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The library is maintained by the Facebook Database Engineering Team, and is based on [LevelDB](https://github.com/google/leveldb), by Sanjay Ghemawat and Jeff Dean at Google.
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This overview gives some simple examples of how RocksDB is used. For the story of why RocksDB was created in the first place, see [Dhruba Borthakur’s introductory talk](https://github.com/facebook/rocksdb/blob/gh-pages-old/intro.pdf?raw=true) from the Data @ Scale 2013 conference.
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## Opening A Database
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A rocksdb database has a name which corresponds to a file system directory. All of the contents of database are stored in this directory. The following example shows how to open a database, creating it if necessary:
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```c++
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#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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...
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```
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If you want to raise an error if the database already exists, add the following line before the rocksdb::DB::Open call:
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```c++
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options.error_if_exists = true;
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```
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## Status
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You may have noticed the `rocksdb::Status` type above. Values of this type are returned by most functions in RocksDB that may encounter
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an error. You can check if such a result is ok, and also print an associated error message:
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```c++
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rocksdb::Status s = ...;
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if (!s.ok()) cerr << s.ToString() << endl;
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```
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## Closing A Database
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When you are done with a database, just delete the database object. For example:
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```c++
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/* open the db as described above */
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/* do something with db */
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delete db;
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```
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## Reads And Writes
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The database provides Put, Delete, and Get methods to modify/query the database. For example, the following code moves the value stored under `key1` to `key2`.
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```c++
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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);
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```
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## Further documentation
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These are just simple examples of how RocksDB is used. The full documentation is currently on the [GitHub wiki](https://github.com/facebook/rocksdb/wiki).
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Here are some specific details about the RocksDB implementation:
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- [RocksDB Overview](https://github.com/facebook/rocksdb/wiki/RocksDB-Overview)
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- [Immutable BlockBased Table file format](https://github.com/facebook/rocksdb/wiki/Rocksdb-BlockBasedTable-Format)
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- [Log file format](https://github.com/facebook/rocksdb/wiki/Write-Ahead-Log-File-Format)
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