To create image thumbnails for all products, you may use “Re-generate all product image thumbnails” link in “Settings → Product images” section.
Sometimes this function may require very much server computing power. When this happens, your hosting company may temporarily suspend your website operation, or the website may become very slow.
To avoid this, slow down the image thumbnails generation function by adding the following line to configuration file wa-config/apps/shop/config.php:
'image_thumb_delay' => 100,
In this example, 100 denotes the delay, expressed in milliseconds, between the calls of the thumbnail generation function. If necessary, change this number to achieve normal operation of your website and to ensure that the image generation does not take too long.
If you do not have file wa-config/apps/shop/config.php on your server, create it with the following contents:
<?php return array( 'image_thumb_delay' => 100, );