This fixes the duplicate url_key issue in a Magento 1.8 / 1.13 installation.

fix-url-keys.php

<?php

/**
 * Drop this into the shell directory in the Magento root and run with -h to see all options.
 */

require_once 'abstract.php';

/**
 * Fix duplicate url keys for categories and products to work with the 1.8 alpha1 CE url key constraints.
 * Run this if the URL Rewrite index does not want to run.
 *
 * @author    Vinai Kopp <[email protected]>
 * @author    Fabrizio Branca <mail@{firstname}-{lastname}.de>
 * @author    Erik Dannenberg <[email protected]>
 */
class Netzarbeiter_Fix_UrlKeys extends Mage_Shell_Abstract
{
    /** @var Mage_Eav_Model_Entity_Attribute */
    protected $_attr;
    /** @var string */
    protected $_qualifyAttrCode;
    /** @var Varien_Db_Adapter_Pdo_Mysql */
    protected $_connection;
    /** @var string */
    protected $_table;

    public function run()
    {
        $this->_showHelp();
        $dupesCat = $this->_gatherDupeUrlKeys('categories');
        $dupesProd = $this->_gatherDupeUrlKeys();

        if ($this->getArg('listProd')) {
            $this->_listDupes($dupesProd);
        } elseif ($this->getArg('listCat')) {
            $this->_listDupes($dupesCat, 'categories');
        } elseif ($this->getArg('fix')) {
            $this->_fixDupes($dupesCat, 'categories');
            if ($this->getArg('qualifyByAttrCode')) {
                $this->_qualifyAttrCode = $this->getArg('qualifyByAttrCode');
            }
            $this->_fixDupes($dupesProd);
        } else {
            die($this->usageHelp());
        }
    }

    protected function _gatherDupeUrlKeys($mode='products')
    {
        $this->_initMode($mode);
        $this->_connection = Mage::getSingleton('core/resource')->getConnection('eav_write');
        /** @var Varien_Db_Select $select */
        $select = $this->_connection->select()->from($this->_table, array(
            'num' => new Zend_Db_Expr('COUNT(*)'),
            'url_key' => 'value',
            'store' => 'store_id'
        ))
            ->where('attribute_id=?', $this->_attr->getId())
            ->group('value')
            ->group('store_id')
            ->order('num')
            ->having('num > 1');
        Mage::getResourceHelper('core')->addGroupConcatColumn($select, 'entities', 'entity_id');
        $result = $this->_connection->fetchAll($select);
        return $result;
    }

    protected function _initMode($mode='products') {
        if ($mode === 'categories') {
            $this->_attr = Mage::getSingleton('eav/config')->getAttribute(Mage_Catalog_Model_Category::ENTITY, 'url_key');
            $this->_table = Mage::getSingleton('core/resource')->getTableName('catalog_category_entity_varchar');
        } else {
            $this->_attr = Mage::getSingleton('eav/config')->getAttribute(Mage_Catalog_Model_Product::ENTITY, 'url_key');
            $this->_table = Mage::getSingleton('core/resource')->getTableName('catalog_product_entity_varchar');
        }
    }

    protected function _listDupes(array $dupes, $mode = 'products')
    {
        $emailMessage = '';
        if (sizeof($dupes) == 0) {
            echo 'No ' . $mode . ' with duplicate url keys found! ^^' . "\n";
            die();
        }
        foreach ($dupes as $row) {
            if ($this->getArg('email')) {
                $productIds = explode(',', $row['entities']);
                $links = array();
                foreach ($productIds as $key => $productId) {
                    $links[] = "<a href='" . Mage::helper('adminhtml')->getUrl(
                            'adminhtml/catalog_product/edit',
                            array('id' => $productId, '_type' => Mage_Core_Model_Store::URL_TYPE_WEB)
                        ) . "'>" . $productId . "</a>";
                }
                $emailMessage .= sprintf(
                        "Found %d %s with url_key '%s':\n %s.\n Store: %s\n", $row['num'], $mode, $row['url_key'],
                        implode("\n", $links),
                        $row['store']
                    )
                    . "\n";
            } else {
                printf(
                    "Found %d %s with url_key '%s': %s. Store: %s\n", $row['num'], $mode, $row['url_key'],
                    $row['entities'],
                    $row['store']
                );
            }
        }
        if (!$emailMessage == '') {
            $this->sendEmail('Duplicate url_keys report', nl2br($emailMessage), 'general', $this->getArg('email'));
        }
    }

    protected function _fixDupes(array $dupes, $mode='products')
    {
        $this->_initMode($mode);
        $processed = array();
        foreach ($dupes as $row) {
            echo "Processing ids: {$row['entities']} for store{$row['store']}\n";
            $ids = explode(',', $row['entities']);
            foreach ($ids as $idx => $entityId) {
                if (0 === $idx && !$this->_qualifyAttrCode) {
                    continue; // keep the first url key unmodified unless --qualifyByAttrCode is set
                }
                if (isset($processed[$entityId])) {
                    echo "Already processed id: {$entityId}. Skipping.\n";
                    continue;
                }
                $key = $this->_qualifyUrlKey($row['url_key'], $entityId);
                echo "$entityId: $key\n";
                $where = array(
                    'attribute_id=?' => $this->_attr->getId(),
                    'entity_id=?' => $entityId,
                    'store_id=?' => $row['store']
                );

                // If record exists in the new table, update it. If not, insert
                if ($this->_recordInNewTableExists($where)) {
                    $this->_updateRow($key, $where);
                } else {
                    $this->_insertRow($entityId, $row['store'], $key);
                }

                // Just for consistency, update the old url_key eav value table, too
                $this->_connection->update($this->_table, array('value' => $key), $where);
                $processed[$entityId]=true;
            }
        }
    }

    protected function _updateRow($value, $where) {
        echo "Updating\n";
        try {
            $this->_connection->update(
                $this->_attr->getBackend()->getTable(), array('value' => $value), $where
            );
        } catch (Exception $e) {
            echo 'ERROR: ' . $e->getMessage() . "\n";
        }
    }

    protected function _insertRow($entityId, $store, $value) {
        echo "Inserting\n";
        try {
            $this->_connection->insert(
                $this->_attr->getBackend()->getTable(),
                array(
                    'entity_type_id' => $this->_attr->getEntityTypeId(),
                    'attribute_id' => $this->_attr->getId(),
                    'entity_id' => $entityId,
                    'store_id' => $store,
                    'value' => $value
                )
            );
        } catch (Exception $e) {
            echo 'ERROR: ' . $e->getMessage() . "\n";
        }
    }

    protected function _recordInNewTableExists(array $where)
    {
        $select = $this->_connection->select()
            ->from($this->_attr->getBackend()->getTable(), array(
                new Zend_Db_Expr('COUNT(*)'),
            ));
        foreach ($where as $cond => $bind) {
            $select->where($cond, $bind);
        }
        $count = $this->_connection->fetchOne($select);
        return (bool) $count;
    }

    protected function _qualifyUrlKey($key, $entityId)
    {
        $sentry = 0;
        $select = $this->_connection->select()->from($this->_table, array(
            new Zend_Db_Expr('COUNT(*)'),
        ))
            ->where('attribute_id=?', $this->_attr->getId())
            ->where('value=:key');
        $candidateBase = $key;
        do {
            if ($sentry++ == 1000) {
                Mage::throwException(sprintf('Unable to qualify url_key "%s": reached 1000 tries', $key));
            }
            if ($sentry == 1 && $this->_qualifyAttrCode) {
                if ($qualifyValue = $this->_getQualifyAttrValue($entityId)) {
                    $candidate = $candidateBase = $key . '-' . $qualifyValue;
                }
            } else {
                $candidate = $candidateBase . '-'. $sentry;
            }
            $bind = array('key' => $candidate);
        } while ($this->_connection->fetchOne($select, $bind));
        return $candidate;
    }

    protected function _getQualifyAttrValue($entityId) {
        $product = Mage::getModel('catalog/product')->load($entityId);
        $attributes = $product->getAttributes();
        $v = $attributes[$this->_qualifyAttrCode]->getFrontend()->getValue($product);
        return iconv("UTF-8", "ASCII//TRANSLIT", strtolower(str_replace(' ', '_', trim($v))));
    }

    /**
     * Send an email
     *
     * @param $subject
     * @param $message
     * @param $sender
     * @param $to
     *
     * @return bool
     */
    protected function sendEmail($subject, $message, $sender, $to)
    {
        try {
            // this is preferred over using Zend_Mail directly, as it will not bypass 3rd party mailer hooks
            // (like mandrill or various smtp senders)
            $template = Mage::getModel('core/email_template');
            // populate the template with data
            $template->setTemplateSubject($subject);
            $template->setTemplateText($message);
            $template->setSenderName(Mage::getStoreConfig('trans_email/ident_' . $sender . '/name'));
            $template->setSenderEmail(Mage::getStoreConfig('trans_email/ident_' . $sender . '/email'));
            $template->isPlain(false);
            if (!$template->send(
                $to,
                null, array()
            )
            ) {
                Mage::log("could not send email with subject {$subject}");

                return false;
            }
        } catch (Exception $e) {
            mage::logException($e);
        }

        return true;
    }

    /**
     * Retrieve Usage Help Message
     *
     */
    public function usageHelp()
    {
        return <<<USAGE
Usage:  php -f fix-url-keys.php
  listProd               List products with duplicate url keys [--email <email address>]
  listCat                List categories with duplicate url keys [--email <email address>]
  fix                    Uniquely qualify duplicate URL keys (default)
                            --qualifyByAttrCode to use attribute value of given attribute code for qualifying
                                    duplicates (will fall back to default number scheme if no value is found)
  help                   This help

USAGE;
    }
}

$shell = new Netzarbeiter_Fix_UrlKeys();
$shell->run();

some-background.md

url_key storage in Magento 1.8

I assume you are basically familiar with Magento's EAV table structure. I'll won't explain that here, only the changes introduces in regards to the url_key attribute in Magento 1.8.

Up to Magento 1.8 the url_key attribute values for products and categories where stored in the table catalog_product_entity_varchar. Uniqueness was only enforced on an application level.

Since Magento 1.8 the values are stored in a new attribute value table called catalog_product_entity_url_key. There uniqueness is enforced on the database level by a unique index on store_id and value (that is, the URL key).

The problem is, the 1.6.1 sample data contains some non-unique url_key values.

When upgrading to 1.8 alpha1, or when installing 1.8 alpha1 with the 1.6.1 sample data, the duplicate url_key values are silently dropped during the migration to the new table (well, all duplicates except one each).

Because of that, the URL rewrite indexer refuses to run.

This script will find the duplicate URL keys using the old values in catalog_product_entity_varchar, uniquely qualify each one, update (or insert) the record into the new catalog_product_entity_url_key table, and then also update the old attribute value table so everything is consistant, even if the old table values aren't used any more (except maybe by third party extensions).

UPDATE: Merged in the store level url_key changes Fabrizio made from here: https://gist.github.com/fbrnc/5464097

UPDATE: Will now also check for categories with duplicate url keys. Added --qualifyByAttrCode, useful if you have products that really should be 2 dimensional but are not.

UPDATE: Merged in the category url_keyfix support from @edannenberg from here: https://gist.github.com/edannenberg/5540108

UPDATE: ability to email basic report.