SELECT 
  * 
FROM 
  cscart_product_feature_variants 
WHERE 
  variant_id IN (
    2908, 2595, 3705, 5136, 2099, 1913, 1858, 
    1862, 1882, 1855, 1879, 5135, 1917, 
    2178, 2230, 2076, 2338, 2945, 1910, 
    5134, 2543, 2127, 2049, 3095, 72, 1834, 
    21, 182, 20, 1856, 1919, 2030, 1859, 
    1870, 137, 434, 62, 11, 1702, 79, 1512, 
    1400, 170, 1813, 0, 3543, 10, 1520, 443, 
    142, 68, 70, 345, 1615
  )

Query time 0.00068

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_product_feature_variants",
          "access_type": "range",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["variant_id"],
          "rows": 54,
          "filtered": 100,
          "index_condition": "cscart_product_feature_variants.variant_id in (2908,2595,3705,5136,2099,1913,1858,1862,1882,1855,1879,5135,1917,2178,2230,2076,2338,2945,1910,5134,2543,2127,2049,3095,72,1834,21,182,20,1856,1919,2030,1859,1870,137,434,62,11,1702,79,1512,1400,170,1813,0,3543,10,1520,443,142,68,70,345,1615)"
        }
      }
    ]
  }
}