$obj = \Magento\Framework\App\ObjectManager::getInstance();
$fileHandler = $obj->create(\Magento\Framework\Logger\Handler\Base::class, ['fileName' => 'var/log/debug.log']);
$logger = $obj->create(\Monolog\Logger::class, [
                'name' => 'save',
                'handlers' => ['file' => $fileHandler],
                'processors' => ['process_id' => $obj->get(\Monolog\Processor\ProcessIdProcessor::class)]
            ]);
$logger->info(var_export(\Magento\Framework\Debug::backtrace(1, 0, 1), 1));

Result could be found in var/log/debug.log

The following solutions helps to find duplicate image file for each product and to remove it.
Create file delete.php in Magento base directory, put the following code into the file.

<?php
include('app/Mage.php');
Mage::app()->setCurrentStore(Mage_Core_Model_App::ADMIN_STORE_ID);
error_reporting(E_ALL | E_STRICT);
ini_set('display_errors', 1);
ob_implicit_flush(1);

$mediaApi  = Mage::getModel("catalog/product_attribute_media_api");
$_products = Mage::getModel('catalog/product')->getCollection();
$i         = 0;
$total     = count($_products);
$count     = 0;
foreach ($_products as $_prod) {
    $_product   = Mage::getModel('catalog/product')->load($_prod->getId());
    $_md5Values = array();

    //protected base image
    $baseImage = $_product->getImage();
    if ($baseImage != 'no_selection') {
        $filePath = Mage::getBaseDir('media') . '/catalog/product' . $baseImage;
        if (file_exists($filePath)) {
            $_md5Values[] = md5(file_get_contents($filePath));
        }
    }

    $i++;
    echo "processing product $i of $total " . PHP_EOL;

    // Loop through product images
    $_images = $_product->getMediaGalleryImages();
    if ($_images) {
        foreach ($_images as $_image) {
            //protected base image
            if ($_image->getFile() == $baseImage) {
                continue;
            }

            $filePath = Mage::getBaseDir('media') . '/catalog/product' . $_image->getFile();
            if (!file_exists($filePath)) {
                continue;
            }
            $md5 = md5(file_get_contents($filePath));
            if (in_array($md5, $_md5Values)) {
                $mediaApi->remove($_product->getId(), $_image->getFile());
                echo 'removed duplicate image from ' . $_product->getSku() . PHP_EOL;
                $count++;
            } else {
                $_md5Values[] = $md5;
            }
        }
    }
}

To launch the script just launch in terminal

>php delete.php

Or visit

http://YourWebsiteURL/delete.php

from your browser.

Thanks to Aadil for a solution.

Reindex category products index at first and then execute following sql-script.

UPDATE `catalog_category_entity_int` AS `status`
INNER JOIN `eav_attribute` AS `attr` ON `attr`.`attribute_code` = 'is_active'
AND `attr`.`entity_type_id` = 3
AND `status`.`attribute_id` = `attr`.`attribute_id`
SET `status`.`value` = IF((SELECT COUNT(`index`.`product_id`)
	FROM `catalog_category_product_index` AS `index`
	WHERE `index`.`category_id` = `status`.`entity_id` GROUP BY `index`.`category_id`) > 0, 1, 0)
WHERE `status`.`store_id` = 0

Magento has two attributes “Set Product As New From Date” and “Set Product As New To Date” to set a product as new. If both fields are empty the product is not new. If only “Set Product As New To Date” is set, the product will be marked as “new” from current time until “Set Product As New To Date”. And If you set only “Set Product As New From Date” attribute the product will be marked as new from that date until forever. But how to check is product “new” currently?

Unfortunately Magento doesn’t have special method for this. But in Mage_Core_Model_Locale model there is a method called isStoreDateInInterval($store, $dateFrom, $dateTo) which checks is current date in two passed dates interval. But we need additional validation two dates are not empty, otherwise that method will return true. So we can create such method in some helper class:

<?php
public function isProductNew(Mage_Catalog_Model_Product $product)
{
    $newsFromDate = $product->getNewsFromDate();
    $newsToDate   = $product->getNewsToDate();
    if (!$newsFromDate && !$newsToDate) {
        return false;
    }
    return Mage::app()->getLocale()
            ->isStoreDateInInterval($product->getStoreId(), $newsFromDate, $newsToDate);
}

If you wan’t automatically make all simple products which are configurable options of configurable products to be hidden in catalog, you have to change their visibility to “Not Visible Individually”.

Next SQL-query will help you with that task.

UPDATE
`catalog_product_entity_int`
SET 
`value` = 1
WHERE
`attribute_id`=(SELECT `attribute_id` FROM `eav_attribute` WHERE `attribute_code` = 'visibility')
AND
`entity_id` IN (SELECT `product_id` FROM `catalog_product_super_link`);

Sometimes you need to work with a production’s DB dump on a staging or on a dev server. To avoid emails be sent to real customers you should replace their email addresses with safe values. We will use Mailinator service which receives all emails and allows to access them if you know full email address.

Just execute this SQL-query in your DB

UPDATE `customer_entity`
SET `email` = CONCAT(
	SUBSTRING(`email`, 1, locate('@', `email`)),
	'mailinator.com'
);

If you need to left your organization domain email addresses unchanged, just add such condition:

UPDATE `customer_entity`
SET `email` = CONCAT(
	SUBSTRING(`email`, 1, locate('@', `email`)),
	'mailinator.com'
)
WHERE  SUBSTRING(`email`, locate('@', `email`) + 1) != 'my-organization.com';

For instance, we need to convert all .gif to .jpg

Execute next commands in terminal

> cd /vaw/www/media/catalog/product/
> for i in $(find $(pwd) -name \*.gif -print); do convert $i $(echo $i.jpg | sed s/.gif//g); done
> rm -r cache/

Then, run these SQL-statements in DB

UPDATE `catalog_product_entity_varchar`
SET `value` = REPLACE(`value`, '.gif', '.jpg') 
WHERE `attribute_id` IN 
    (SELECT `attribute_id` FROM `eav_attribute`
        WHERE `attribute_code` IN ('image', 'small_image', 'thumbnail') AND `entity_type_id` = 4
    )
; 
UPDATE `catalog_product_entity_media_gallery`
SET `value` = REPLACE(`value`, '.gif', '.jpg');