SELECT 
  cscart_products.*, 
  cscart_products.ebay_status, 
  cscart_products.ebay_template_id 
FROM 
  cscart_products 
WHERE 
  cscart_products.product_id IN (
    20941, 20942, 20943, 20944, 20945, 20946, 
    20947, 20948, 20949, 20950, 20951, 
    20952, 20953, 20954, 20955, 20956
  )

Query time 0.00029

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_products",
      "access_type": "range",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "3",
      "used_key_parts": ["product_id"],
      "rows": 16,
      "filtered": 100,
      "index_condition": "cscart_products.product_id in (20941,20942,20943,20944,20945,20946,20947,20948,20949,20950,20951,20952,20953,20954,20955,20956)"
    }
  }
}