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Daniele Alessandri
100 lines
5.4 KiB
Markdown
100 lines
5.4 KiB
Markdown
# Some frequently asked questions about Predis #
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### What is the point of Predis? ###
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The main point of Predis is about offering a highly customizable client for Redis that can be easily
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extended by developers while still being reasonabily fast. With Predis you can swap almost any class
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used internally with your own custom implementation: you can build connection classes, or new
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distribution strategies for client-side sharding, or class handlers to replace existing commands or
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add new ones. All of this can be achieved without messing with the source code of the library and
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directly in your own application. Given the fast pace at which Redis is developed and adds new
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features, this can be a great asset that allows you to add new and still missing features or commands,
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or change the behaviour of the library without the need to break your dependencies in production code
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(well, at least to some degree).
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### How about performances? ###
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Please refer to the dedicated __FAQ.PERFORMANCES__ file.
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### Why PHP 5.3? ###
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Seriously, are you still using PHP 5.2 to build new applications? I assume that if you are throwing Redis
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in the mix, then you are probably coding something new after all. PHP 5.3 is faster, less memory hungry
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and has a few nice features such as namespaces and closures (kind of). More importantly, PHP 5.2 is not
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even officially supported anymore (aside from security patches). PHP 5.3 is not the future of PHP, but
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its current present. Furthermore, most of the existing frameworks out there are also making the switch
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with their respective new major versions. If you still insist on using PHP 5.2, you can get any recent
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backported release of Predis 0.6.x, or just use a different library.
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### Why so many files for just one library? ###
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Before v0.7, Predis used the one-big-file approach to distribute the library. As much as you prefer having
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just one file for everything, this kind of solution is actually not that good. Predis now complies with the
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[PSR-0](http://groups.google.com/group/php-standards/web/psr-0-final-proposal) standard to play nice with
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the major recent frameworks and libraries, so it needs an autoloader function to be defined. If you still
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want to have just one file grouping all the classes for whatever reason, then the __bin/create-single-file.php__
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script in the repository can generate it for you. There is also the __bin/create-phar.php__ script that
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generates a single [Phar archive](http://www.php.net/manual/en/intro.phar.php) of the whole library.
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### Does Predis support UNIX domain sockets and persistent connections? ###
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Yes. Obviously, persistent connections actually work when using PHP configured as a persistent process that
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gets recycled between requests (see [PHP-FPM](http://php-fpm.org/)).
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### Does Predis support transparent (de)serialization of values? ###
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No, and it will not ever do that for you by default. The reason behind this decision is that serialization
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is usually something that developers prefer to customize depending on their needs and can not be easily
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generalized when using Redis because of the many possible access patterns for the data. This does not
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mean that it is impossible to have such a feature, you can leverage Predis' extensibility to define your
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own serialization-aware commands. See [here](http://github.com/nrk/predis/issues/29#issuecomment-1202624)
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for more details on how to implement such a feature with a practical example.
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### How can I force Predis to connect to Redis before sending any command? ###
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Explicitly connecting to Redis is usually not needed since the client library relies on lazily initialized
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connections to the server, but this behavior can be inconvenient in certain scenarios when you absolutely
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need to do an upfront check to detect if the server is up and running and eventually catch exceptions on
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failures. In this case developers can use `Predis\Client::connect()` to explicitly connect to the server:
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```
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$client = new Predis\Client();
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try {
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$client->connect();
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} catch (Predis\Connection\ConnectionException $exception) {
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// We could not connect to Redis! Your handling code goes here.
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}
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$client->info();
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```
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### How Predis implements abstraction of Redis commands? ###
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The approach used in Predis to implement the abstraction of Redis commands is quite simple. By default
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every command in the library follows exactly the same argument list as defined in the great online
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[Redis documentation](http://redis.io/commands) which makes things pretty easy if you already know how
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Redis works or if you need to look up how to use certain commands. Alternatively, variadic commands can
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accept an array for keys or values (depending on the command) instead of a list of arguments. See for
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example how [RPUSH](http://redis.io/commands/rpush) or [HMSET](http://redis.io/commands/hmset) work:
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```
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$client->rpush('my:list', 'value1', 'value2', 'value3'); // values as arguments
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$client->rpush('my:list', array('value1', 'value2', 'value3')); // values as single argument array
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$client->hmset('my:hash', 'field1', 'value1', 'field2', 'value2'); // values as arguments
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$client->hmset('my:hash', array('field1'=>'value1', 'field2'=>'value2'); // values as single named array
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```
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The only exception to this _rule_ is the [SORT](http://redis.io/commands/sort) command for which modifiers are
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[passed using a named array](https://github.com/nrk/predis/blob/master/tests/Predis/Command/KeySortTest.php#L56-77).
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