PHP-LevelDB: The PHP Binding for LevelDB

Requirements

• PHP >= 5.2
• LevelDB

You could get leveldb from: http://code.google.com/p/leveldb/

$ wget http://leveldb.googlecode.com/files/leveldb-1.5.0.tar.gz
$ tar zxvf leveldb-1.5.0.tar.gz
$ cd leveldb-1.5.0
$ make

NOTE LevelDB didn't have make install target in Makefile: http://code.google.com/p/leveldb/issues/detail?id=27， If you want to install to a specific dir, you could: make INSTALL_PATH=/Your/Path/

Installation

$ git clone https://github.com/reeze/php-leveldb.git
$ cd php-leveldb
$ phpize
$ ./configure --with-leveldb=/path/to/your/leveldb-1.*.*
$ make
$ make install

1. Install from PECL

   PHP-LevelDB havn't been hosted in PECL Yet

Usage

Since PHP-LevelDB is a binding for LevelDB, most of the interface are the same as LevelDB document: http://leveldb.googlecode.com/git/doc/index.html

Open options

When open a leveldb database you could specify options to override default value:

<?php
/* default open options */
$options = array(
	'create_if_missing' => true,	// if the specified database didn't exist will create a new one
	'error_if_exists'	=> false,	// if the opened database exsits will throw exception
	'paranoid_checks'	=> false,
	'block_cache_size'	=> 8 * (2 << 20),
	'write_buffer_size' => 4<<20,
	'block_size'		=> 4096,
	'max_open_files'	=> 1000,
	'block_restart_interval' => 16,
	'compression'		=> LEVELDB_SNAPPY_COMPRESSION,
	'comparator'		=> NULL,   // any callable parameter return 0, -1, 1
);
/* default readoptions */
$readoptions = array(
	'verify_check_sum'	=> false,
	'fill_cache'		=> true,
);

/* default write options */
$writeoptions = array(
	'sync' => false
);

$db = new LevelDB("/path/to/db", $options, $readoptions, $writeoptions);

NOTE The readoptions and writeoptions will take effect when operate on db afterward, but you could override it by specify read/write options when accessing

Using custom comparator

You could write your own comparator, the comparator can be anything callale in php it the same as usort()'s compare function: http://php.net/usort, and the comparator could be:

<?php
int callback(string $a, string $b );
$db = new LevelDB("/path/to/db", array('comparator' => 'cmp'));
function cmp($a, $b)
{
	return strcmp($a, $b);
}

NOTE If you create a database with custom comparator, you can only open it again with the same comparator.

Basic operations: get(), put(), delete()

LevelDB is a key-value database, you could do those basic operations on it:

<?php

$db = new LevelDB("/path/to/leveldb-test-db");

/*
 * Basic operate methods: set(), get(), delete()
 */
$db->put("Key", "Value");
$db->set("Key2", "Value2"); // set() is an alias of put()
$db->get("Key");
$db->delete("Key");

NOTE Some key-value db use set instead of put to set value, so if like set(), you could use set() to save value.

Write in a batch

If you want to do a sequence of update and want to make it atomically, then writebatch will be your friend.

The WriteBatch holds a sequence of edits to be made to the database, and these edits within the batch are applied in order.

Apart from its atomicity benefits, WriteBatch may also be used to speed up bulk updates by placing lots of individual mutations into the same batch.

<?php

$db = new LevelDB("/path/to/leveldb-test-db");

$batch = new LevelDBWriteBatch();
$batch->put("key2", "batch value");
$batch->put("key3", "batch value");
$batch->set("key4", "a bounch of values"); // set() is an alias of put()
$batch->delete("some key");

// Write once
$db->write($batch);

Iterate throught db

You can iterate through the whole database by iteration:

<?php

$db = new LevelDB("/path/to/leveldb-test-db");
$it = new LevelDBIterator($db);

// Loop in iterator style
while($it->valid()) {
	var_dump($it->key() . " => " . $it->current() . "\n");
}

// Or loop in foreach
foreach($it as $key => $value) {
	echo "{$key} => {$value}\n";
}

if you want to iterate by reverse order, you could:

<?php

$db = new LevelDB("/path/to/leveldb-test-db");
$it = new LevelDBIterator($db);

for($it->last(); $it->valid(); $it->prev()) {
	echo "{$key} => {$value}\n";
}

/*
 * And you could seek with: rewind(), next(), prev(), seek()
 */

NOTE In LevelDB LevelDB::seek() will success even when the key didn't exists, it will seek to the latest key: db-with-key('a', 'b', 'd', 'e'); $db->seek('c'); iterator will point to key 'd'

Operations on database

LevelDB::close()

Since leveldb can only accessed by a single proccess once, so you may want to close it when you don't use it anymore.

<?php

$db = new LevelDB("/path/to/leveldb-test-db");
$it = new LevelDBIterator($db);
$db->close();
$it->next();				// noop you can't do that, exception thrown
$db->set("key", "value");	// you can't do this either

after database closed, you can't do anything related to it;

LevelDB::destroy()

If you want to destroy a database, you could delete the whole database by hand: rm -rf /path/to/db or you could use LevelDB::destroy('/path/to/db').

Be careful with this.

LevelDB::repair()

If you can't open a database, neither been locked or other error, if it's corrupted, you could use LevelDB::repair('/path/to/db') to repair it. it will try to recover as much data as possible.

Reference

More info could be found at:

• LevelDB project home: http://code.google.com/p/leveldb/
• LevelDB document: http://leveldb.googlecode.com/git/doc/index.html
• A LevelDB internals analysis in Chinese http://dirlt.com/LevelDB.html 推荐关注博主的博客

License

PHP-LevelDB is licensed under PHP License