我有一个表,对于给定的'{{1,2},{3,4},{5,6}'
元组,它存储了几个指标:
(time, country, asn)
在一般使用过程中,我将这些指标中的每一个规范化为0到100之间的值,然后返回最大值,以便粗略估计该国家与该ASN的连接“有多好”:
+----------+---------+-------+-------+--------+--------+
| 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 |
| .... | ... | ... | ... | .... | .... |
有时,我可以使用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"
(对该国家/地区的ASN请求数)列进行加权,以执行加权平均值:
reqs
此查询完美无缺。然而,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
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
这引发了错误:
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
我可以毫无问题地执行更简单的子查询。为什么这个失败了,我该如何解决?
我正在使用MariaDB,ERROR 1815 (HY000): Internal error: Lost connection to ExeMgr. Please contact your administrator
表使用ColumnStore引擎。
当我用metrics
替换WHERE t1.avg_quality < 50
时,查询执行时没有问题。因此,执行子查询或过滤没有问题。当我尝试过滤计算列失败时,这是严格的。
答案 0 :(得分:0)
我联系了我公司的DBA,看看他们是否有任何答案或建议。他们无法为行为提供解释,但他们能够提供解决方法:
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
HAVING
avg_quality < 50
) t1