Magento Admin > CMS > Pages > Manage Content image insertion fails
If when attempting to insert an image via the WYSIWYG editor images are not
listed, or take a very long time to display, this is likely due to MySQL scanning
through the large number of rows in the
core_file_storage table matching
directory = 'wysiwyg' without using an index.
To fix this issue, add the following index to your Magento database:
CREATE INDEX IDX_CORE_FILE_STORAGE_DIRECTORY ON core_file_storage (directory ASC);
If you are using a table prefix you will need to adjust the above command to include the prefix.