MySQL Query IN（）子句在索引列上变慢

Question

我有一个由PHP脚本生成的MySQL查询，该查询将如下所示：

SELECT * FROM Recipe_Data WHERE 404_Without_200 = 0 AND Failures_Without_Success = 0 AND RHD_No IN (10, 24, 34, 41, 43, 51, 57, 59, 61, 67, 84, 90, 272, 324, 402, 405, 414, 498, 500, 501, 510, 559, 562, 595, 632, 634, 640, 643, 647, 651, 703, 714, 719, 762, 765, 776, 796, 812, 814, 815, 822, 848, 853, 855, 858, 866, 891, 920, 947, 956, 962, 968, 1049, 1054, 1064, 1065, 1070, 1100, 1113, 1119, 1130, 1262, 1287, 1292, 1313, 1320, 1327, 1332, 1333, 1335, 1340, 1343, 1344, 1346, 1349, 1352, 1358, 1362, 1365, 1482, 1495, 1532, 1533, 1537, 1549, 1550, 1569, 1571, 1573, 1574, 1596, 1628, 1691, 1714, 1720, 1735, 1755, 1759, 1829, 1837, 1844, 1881, 1919, 2005, 2022, 2034, 2035, 2039, 2054, 2076, 2079, 2087, 2088, 2089, 2090, 2091, 2092, 2154, 2155, 2156, 2157, 2160, 2162, 2164, 2166, 2169, 2171, 2174, 2176, 2178, 2179, 2183, 2185, 2186, 2187, 2201, 2234, 2236, 2244, 2245, 2250, 2255, 2260, 2272, 2280, 2281, 2282, 2291, 2329, 2357, 2375, 2444, 2451, 2452, 2453, 2454, 2456, 2457, 2460, 2462, 2464, 2465, 2467, 2468, 2469, 2470, 2473, 2474, 2481, 2485, 2487, 2510, 2516, 2519, 2525, 2540, 2545, 2547, 2553, 2571, 2579, 2580, 2587, 2589, 2597, 2602, 2611, 2629, 2660, 2662, 2700, 2756, 2825, 2833, 2835, 2858, 2958, 2963, 2964, 3009, 3090, 3117, 3118, 3120, 3121, 3122, 3123, 3126, 3127, 3129, 3130, 3133, 3135, 3137, 3138, 3139, 3141, 3142, 3145, 3146, 3147, 3151, 3152, 3155, 3193, 3201, 3204, 3219, 3221, 3222, 3223, 3224, 3225, 3226, 3227, 3228, 3229, 3231, 3232, 3233, 3234, 3235, 3237, 3239, 3246, 3250, 3253, 3259, 3261, 3291, 3315, 3328, 3377, 3381, 3383, 3384, 3385, 3387, 3388, 3389, 3390, 3396, 3436, 3463, 3465, 3467, 3470, 3471, 3484, 3507, 3515, 3554, 3572, 3641, 3672, 3683, 3689, 3690, 3692, 3693, 3694, 3697, 3698, 3705, 3711, 3713, 3715, 3716, 3717, 3719, 3720, 3722, 3726, 3727, 3732, 3737, 3763, 3767, 3770, 3771, 3772, 3773, 3803, 3810, 3812, 3816, 3846, 3847, 3848, 3851, 3874, 3882, 3902, 3903, 3906, 3908, 3916, 3924, 3967, 3987, 4006, 4030, 4043, 4045, 4047, 4058, 4067, 4107, 4108, 4114, 4115, 4131, 4132, 4133, 4137, 4138, 4139, 4140, 4141, 4142, 4146, 4150, 4151, 4152, 4153, 4157, 4158, 4160, 4163, 4166, 4167, 4171, 4179, 4183, 4221, 4225, 4242, 4257, 4435, 4437, 4438, 4443, 4446, 4449, 4450, 4451, 4452, 4454, 4460, 4550, 4557, 4618, 4731, 4775, 4804, 4972, 5025, 5026, 5039, 5042, 5294, 5578, 5580, 5599, 5602, 5649, 5726, 5779, 5783, 5931, 5934, 5936, 5939, 5940, 5941, 5978, 6044, 6056, 6113, 6116, 6118, 6122, 6123, 6125, 6127, 6128, 6129, 6130, 6131, 6135, 6141, 6145, 6147, 6150, 6152, 6153, 6154, 6160, 6166, 6169);

RHD_No列是此数据库的主键，总共约有40万行。问题是，查询速度非常慢，通常需要2秒钟左右，但我发现查询的时间长达10秒钟。

当我尝试解释查询时，一切似乎都应该没问题：

+----+-------------+-------------+-------+---------------+---------+---------+------+------+-------------+
| id | select_type | table       | type  | possible_keys | key     | key_len | ref  | rows | Extra       |
+----+-------------+-------------+-------+---------------+---------+---------+------+------+-------------+
|  1 | SIMPLE      | Recipe_Data | range | PRIMARY       | PRIMARY | 4       | NULL |  420 | Using where |
+----+-------------+-------------+-------+---------------+---------+---------+------+------+-------------+

当我配置查询时，我得到：

mysql> show profile;
+--------------------------------+----------+
| Status                         | Duration |
+--------------------------------+----------+
| starting                       | 0.000015 |
| checking query cache for query | 0.000266 |
| Opening tables                 | 0.000009 |
| System lock                    | 0.000004 |
| Table lock                     | 0.000006 |
| init                           | 0.000115 |
| optimizing                     | 0.000038 |
| statistics                     | 0.000797 |
| preparing                      | 0.000047 |
| executing                      | 0.000002 |
| Sending data                   | 2.675270 |
| end                            | 0.000007 |
| query end                      | 0.000003 |
| freeing items                  | 0.000071 |
| logging slow query             | 0.000002 |
| logging slow query             | 0.000058 |
| cleaning up                    | 0.000005 |
+--------------------------------+----------+

我已经在这个问题上研究了很长时间了，但一直没有找到解决方案。这个查询有什么明显的错误吗？我看不到查看420行应该花2秒钟以上的时间。

Answer 1

您正在通过主键访问420行，这可能会导致索引访问路径。每个键可以访问2个索引页和一个数据页。如果它们在缓存中，则查询应运行得很快。否则，对磁盘的每个页面访问都会产生通常的磁盘延迟。如果我们假设磁盘延迟为5毫秒，高速缓存命中率为80％，则得出的时间为420 * 3 * 0.2 * 5ms = 1.2秒，与您看到的顺序相同。