昨晚在线用户急剧增加后，我遇到了mysql CPU使用问题。平均服务器负载为150(1分钟)，top中mysql CPU使用率为3500-4000%。显示进程列表；结果是 250 个查询。以下是一些设置和状态:
max_connections=400
query_cache_type=1
join_buffer_size=4096
query_cache_size=5M
query_cache_limit=1048576
query_cache_min_res_unit=4096
这里是执行
show status like '%qcach%';
30秒内3次
+-------------------------+------------+
| Variable_name | Value |
+-------------------------+------------+
| Qcache_free_blocks | 597 |
| Qcache_free_memory | 1658184 |
| Qcache_hits | 1813237610 |
| Qcache_inserts | 456473072 |
| Qcache_lowmem_prunes | 433310255 |
| Qcache_not_cached | 105476947 |
| Qcache_queries_in_cache | 1564 |
| Qcache_total_blocks | 4027 |
+-------------------------+------------+
+-------------------------+------------+
| Variable_name | Value |
+-------------------------+------------+
| Qcache_free_blocks | 429 |
| Qcache_free_memory | 1422288 |
| Qcache_hits | 1813245095 |
| Qcache_inserts | 456475419 |
| Qcache_lowmem_prunes | 433312602 |
| Qcache_not_cached | 105477523 |
| Qcache_queries_in_cache | 1553 |
| Qcache_total_blocks | 3896 |
+-------------------------+------------+
+-------------------------+------------+
| Variable_name | Value |
+-------------------------+------------+
| Qcache_free_blocks | 481 |
| Qcache_free_memory | 1546088 |
| Qcache_hits | 1813254695 |
| Qcache_inserts | 456477824 |
| Qcache_lowmem_prunes | 433314721 |
| Qcache_not_cached | 105478263 |
| Qcache_queries_in_cache | 1699 |
| Qcache_total_blocks | 4146 |
+-------------------------+------------+
服务器配置:
2 x Intel(R) Xeon(R) CPU E5-2650 v4 @ 2.20GHz.
64GB RAM
Mysql running on SSDs.
最佳答案
我已将query_cache_size更改为128M。 mysql 进程使用的 CPU 比以前少得多。
冲洗状态2分钟后结果:
| Qcache_free_blocks | 15777 |
| Qcache_free_memory | 66772864 |
| Qcache_hits | 74013 |
| Qcache_inserts | 5293 |
| Qcache_lowmem_prunes | 0 |
| Qcache_not_cached | 5125 |
| Qcache_queries_in_cache | 37880 |
| Qcache_total_blocks | 92907
但是，5-10分钟后Qcache_lowmem_prunes再次开始增加(可能比以前慢，但仍然以每秒50-100点的速度增加)。
我认为问题不再是query_cache_size。
冲水后7分钟:
| Qcache_free_blocks | 14825 |
| Qcache_free_memory | 54665504 |
| Qcache_hits | 534784 |
| Qcache_inserts | 44569 |
| Qcache_lowmem_prunes | 6194 |
| Qcache_not_cached | 34718 |
| Qcache_queries_in_cache | 49212 |
| Qcache_total_blocks | 114243 |
+-------------------------+----------+
AVG Query Size = 1616
Frag Indicator = 12.98%
Utilisation = 59.27%
Removal Ratio = 13.9%
Hit Rate = 87.09%
之后我将 query_cache_min_res_unit 更改为 2048。 冲洗后10分钟状态:
| Qcache_free_blocks | 21987 |
| Qcache_free_memory | 38858856 |
| Qcache_hits | 255849 |
| Qcache_inserts | 20100 |
| Qcache_lowmem_prunes | 15638 |
| Qcache_not_cached | 16691 |
| Qcache_queries_in_cache | 64573 |
| Qcache_total_blocks | 152132 |
AVG Query Size = 1477
Frag Indicator = 14.45%
Utilisation = 71%
Removal Ratio = 79%
Hit Rate = 87%
关于Mysql 进程 CPU 使用率超过 3500%，Qcache_lowmem_prunes 过高，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/48923630/