我有一个表,对于给定的(time, country, asn)
元组,它存储了几个指标:
+----------+---------+-------+-------+--------+--------+
| time | country | asn | rtt | rexb | reqs |
+----------+---------+-------+-------+--------+--------+
| 10000000 | US | 12345 | 40 | 0.05 | 5000 |
| 10000000 | US | 54321 | 120 | 0.15 | 500 |
| 10000000 | MX | 12345 | 300 | 0.25 | 1000 |
| 10000000 | MX | 54321 | 160 | 0.10 | 200 |
| .... | ... | ... | ... | .... | .... |
在一般使用期间,我将这些指标中的每一个标准化为 0 到 100 之间的值,然后返回最大值,以便粗略估计该国家与 ASN 的连接“有多好”:
SELECT
country,
asn,
least(
-- least(100, greatest(0, ...)) = clip value between 0 and 100
least(100, greatest(0,
-- normalize and protect against null values
-- sample normalization:
-- 0 ms RTT = "100% good"
-- 300 ms RTT = "0% good"
coalesce((300 - rtt) / 3, 0)
)),
least(100, greatest(0,
-- sample normalization:
-- 0% REXB = "100% good"
-- 50% REXB = "0% good"
coalesce((0.5 - rexb) / 0.5, 0)
)),
-- Other metrics may follow
) as quality
FROM
metrics
WHERE
time = 10000000 -- "current time"
有时我可能会通过使用reqs
(对该国家/地区的请求数+ASN)列进行加权来执行加权平均:
SELECT
country,
least(
least(100, greatest(0,
coalesce((300 - sum(rtt*reqs)/sum(reqs)) / 3, 0)
)),
least(100, greatest(0,
coalesce((0.5 - sum(rexb*reqs)/sum(reqs)) / 0.5, 0)
))
) as avg_quality
FROM
metrics
WHERE
time = 10000000 -- "current time"
GROUP BY
country
此查询完美运行。但是,当我尝试在子查询中使用它时,我遇到了一个问题。
我的目标是找出有多少国家的“平均质量”低于某个阈值:
SELECT
count(*)
FROM (
SELECT
country,
least(
least(100, greatest(0,
coalesce((300 - sum(rtt*reqs)/sum(reqs)) / 3, 0)
)),
least(100, greatest(0,
coalesce((0.5 - sum(rexb*reqs)/sum(reqs)) / 0.5, 0)
))
) as avg_quality
FROM
metrics
WHERE
time = 10000000 -- "current time"
GROUP BY
time, country
) t1
WHERE t1.avg_quality < 50
这引发了错误:
ERROR 1815 (HY000): Internal error: Lost connection to ExeMgr. Please contact your administrator
我可以毫无问题地执行更简单的子查询。为什么这个失败,我该如何解决?
我正在使用 MariaDB,并且该metrics
表使用 ColumnStore 引擎。
快速更新
当我WHERE t1.avg_quality < 50
用WHERE country = "US"
查询替换时执行没有问题。所以执行子查询或过滤没有问题。严格来说,当我尝试过滤计算列时它会失败。