Asynchronous PHP MySQL Query Library
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README.mdown

Spider

Spider is a PHP library offering asynchronous MySQL querying. While there are other ways to achieve this, such as mysqlnd or pthreads, Spider was built to have no outside dependencies except for a connection to a MySQL database.

Usage

Install the latest version with composer require jessecascio/spider

<?php

use Spider\Connection;
use Spider\Component;

// build an array of queries
$queries   = array();
$queries[] = "SELECT SLEEP(FLOOR(0 + (RAND() * 1)))";
$queries[] = "SELECT SLEEP(FLOOR(0 + (RAND() * 1)))";
$queries[] = "SELECT SLEEP(FLOOR(0 + (RAND() * 1)))";

// create a MySQL Connection
$connection = new Connection\MySQL($dbname, $usr, $pwd, $host, $port);

// execute
$web = new Component\Web($connection);
$web->queries($queries);
$web->crawl();

// proceed
$web->results();

Concepts

Since PHP does not natively support threading, or parallel execution, Spider takes the queries and processes them in their own process. After the query executes, it is placed into temporary storage until all queries have completed. Once all queries are done, the results are returned to the calling process.

Docs

Configurations

With the use of multiple processes it becomes very important to control both the number and the size of the processes. Also, by defining a log output, errors can be correctly logged during process failure.

use Spider\Component;

$config = new Component\Config();
$config->processes(5);
$config->memory(100); // MB
$config->trace('/path/to/log');

$web = new Component\Web($connection, $config);

Alternatively these can be loaded from an .ini file to allow for different settings in different environments.

use Spider\Component;

$config = new Component\Config();
$config->parse('/path/to/file.ini');

Storage

By default Spider will store results in a temporary MySQL table. There are however other Storage objects. For example, if you would rather have results stored in Memcached, simply instantiate the correct Storage object

use Spider\Component;
use Spider\Storage;

$memcached = new Storage\Memcached($host, $port);

$config = new Component\Config();
$config->storage($memcached);

Callbacks

Often times it is beneficial to process queries as they complete and not have to wait until all queries are done. This can be done with either a single callback applied to all queries, or specific callbacks mapped to query keys.

// single callback
$web->crawl(function($data) {
    // do work
    return $data;
});

// multiple callbacks
$queries = array();
$queries['users']  = "SELECT * FROM users";
$queries['orders'] = "SELECT * FROM orders"

$web->queries($queries);
$web->crawl([
    'users' => function ($data) {
        // do work on users data
        return $data;
    },
    'orders' => function ($data) {
        // do work on orders data
        return $data;
    }
])

Considerations

Special considerations will need to be made for the number of processes to run and that allowed size. Since most web servers are limited on resources you need to ensure that Spider does not spin up too many processes and that those processes do not get too large. With can be done with the Component\Config object.

There is additional overhead for running the queries in this manner. Not only the cost of spinning up and monitoring the processes, but also of all the additional reads and writes into the temporary storages. Typically Spider would not be beneficial unless your total query time is over 1s. Some good use cases for Spider are querying a large horizontal star table where each component can be queried individually, to return to PHP for aggregation building, or for querying across multiple shards.

Testing should be done to determine optimal process count/size and typical return times on batch queries.