This is just a quick and simple script for importing MySQL data into a Solr index. Very basic and only handles data in a single table; if your data is spread across multiple tables using JOINs, etc, then you're out of luck. Feel free to repurpose any of this code to fit your specific needs.

mysql2solr.php

<?php
// A quick and dirty script for bulk importing MySQL data into a Solr index

// Edit this array with the MySQL fields that will be sent to the SOLR index
// The key is the name of the MySQL column and the value is its respective Solr field
//
// Example: 'mysql_col_name' => 'solr_field'
//
$field_mappings = array(
	'id'			=> 'id',
	'name'			=> 'name',
	'manufacturer'		=> 'manufacturer',
	'description'		=> 'description',
	'created_at'		=> 'created_at',
);

// Edit these fields to match your database:
const DB_HOST     	= 'localhost';
const DB_USERNAME 	= 'admin';
const DB_PASSWORD 	= 'password';
const DB_DBNAME   	= 'database';
const DB_TABLE    	= 'table';

// Edit these fields to match your Solr index:
const SOLR_PROTOCOL 	= 'http://';
const SOLR_HOST 	= 'localhost';
const SOLR_PORT 	= 8080;
const SOLR_LOCATION 	= '/solr';

// Set your batch size. Note that if the fields you're sending have lots of text
// it may get truncated or timed out:
const BATCH_SIZE = 10;


// ----------------------------------------------------
// Begin importation process:
// ----------------------------------------------------

$batch 		= 0;					// A counter for the number of items in the batch
$total 		= 0;					// A counter for the total items processed
$xmlString 	= "<add>\n";				// An XML string of data to send to the Solr index

// A MySQL query to select the indexed fields from the database:
$query 		= "SELECT " . implode(",", $field_mappings) . " FROM " . DB_TABLE;

$result 	= dbquery($query);			// The matching data from the db
$totals 	= mysql_num_rows($result);		// The total number of matching rows in the db

// Iterate through the data and build 
while ($row = mysql_fetch_assoc($result)) {
	$xmlString .= "\t<doc>\n";
	foreach ($field_mappings as $mysql_col => $solr_field) {
		$xmlString .= "\t\t<field name=\"" . $solr_field . "\">" . $row[$mysql_col] . "</field>\n";
	}
	$xmlString .= "\t</doc>\n";
	$batch++;
	$total++;
	if ($batch == BATCH_SIZE || $total == $totals) {
		$batch = 0;
		$xmlString .= "</add>\n\n";
		$server_status = sendXML($xmlString);
		if ($server_status['status'] == TRUE) {
			print "Successfully sent " . $batch . " rows to the Solr index. Server returned: " . $server_status['message'] . "<br />";
			$xmlString = "<add>\n";
		}
		else {
			print "Script reached an error. cURL returned the following message: " . $server_status['message'] . "<br />Stopping";
			exit();
		}
	}
}

/*
	A helper function for making MySQL queries
	Input: A MySQL query
	Return: The query results
*/
function dbquery($query) {
	mysql_connect(DB_HOST, DB_USERNAME, DB_PASSWORD) or die(mysql_error());
	mysql_select_db(DB_DBNAME) or die(mysql_error());
	return mysql_query($query);
}

/*
	A helper function for sending data to the Solr index
	Input: An XML-formatted string to send to the Solr index
	Return: An array containing a return status and message

	Adapted from code by  Robert Capra
	http://www.ils.unc.edu/~rcapra/solr-update-php.php
*/
function sendXML($xmlString) {
	$url = SOLR_PROTOCOL . SOLR_HOST . ":" . SOLR_PORT . SOLR_LOCATION . "/update";

	print "Sending the following data to " . $url . ": " . $xmlString;

	$header = array("Content-type:text/xml; charset=utf-8");
	$ch = curl_init();
	curl_setopt($ch, CURLOPT_URL, $url);
	curl_setopt($ch, CURLOPT_HTTPHEADER, $header);
	curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
	curl_setopt($ch, CURLOPT_POST, 1);
	curl_setopt($ch, CURLOPT_POSTFIELDS, $xmlString);
	curl_setopt($ch, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_1_1);
	curl_setopt($ch, CURLINFO_HEADER_OUT, 1);
	$data = curl_exec($ch);

	if (curl_errno($ch)) {
	   return array('status' => FALSE, 'message' => curl_error($ch));
	} else {
	   curl_close($ch);
	   return array('status' => TRUE, 'message' => $data);
	}
}
?>

Websolr customers should use the following settings:

const SOLR_PROTOCOL = 'http://';
const SOLR_HOST = 'YOUR_SUBDOMAIN.websolr.com';
const SOLR_PORT = 80;
const SOLR_LOCATION = '/solr/YOUR_API_KEY';

For example:

const SOLR_PROTOCOL = 'http://';
const SOLR_HOST = 'ec2-west.websolr.com';
const SOLR_PORT = 80;
const SOLR_LOCATION = '/solr/1a2b3c4d5e';