当前状态
我们有一个运行2个多小时的查询。在检查进度时,查询在表T5的连接期间和查询的最后阶段花费了大量时间。有什么办法可以简化这个查询吗?我无法使用聚合函数代替rank(),因为使用的orderby有点复杂。
我们已经尝试过的
我们已经将子查询转换为select子句中的case语句,并且有助于减少执行时间,但这并不重要。我们简化了T3,T4和T6的共同相关查询。
SELECT * FROM
(SELECT T2.f1, T2.f2 .... T5.f19, T5.f20,
case when T1.trxn_id is null then T2.crt_ts
when T1.trxn_id is not null and T5.acct_trxn_id is not null and T2.crt_ts >= T5.crt_ts then T2.crt_ts
when T1.trxn_id is not null and T5.acct_trxn_id is not null and T2.crt_ts < T5.crt_ts then T5.crt_ts
end as crt_ts ,
row_number() over ( partition by T2.w_trxn_id,
if(T1.trxn_id is null, 'NULL', T1.trxn_id)
order by T2.business_effective_ts desc,
case when T1.trxn_id is null then T2.crt_ts
when T1.trxn_id is not null and T5.acct_trxn_id is not null and T2.crt_ts >= T5.crt_ts then T2.crt_ts
when T1.trxn_id is not null and T5.acct_trxn_id is not null and T2.crt_ts < T5.crt_ts then T5.crt_ts
when T1.trxn_id is not null and T5.acct_trxn_id is null then T2.crt_ts end desc
) as rnk
FROM(SELECT * FROM T3 WHERE title_name = 'CAPTURE' and tr_dt IN (SELECT tr_dt FROM DT_LKP))
T2
LEFT JOIN (SELECT * FROM T6 WHERE tr_dt IN (SELECT tr_dt FROM DT_LKP))
T1 ON T2.w_trxn_id = T1.w_trxn_id AND T2.business_effective_ts = T1.business_effective_ts
LEFT JOIN (SELECT f1, f3. ... f20 FROM T4 WHERE tr_dt IN (SELECT tr_dt FROM DT_LKP))
T5 ON T1.trxn_id = T5.acct_trxn_id
WHERE if(T1.trxn_id is null, 'NULL', T1.trxn_id) = if(T5.acct_trxn_id is null, 'NULL', T5.acct_trxn_id)
) FNL WHERE rnk = 1
不确定这对你有多大帮助。有一些相当奇怪的WHERE子句:
WHERE if(T1.trxn_id is null, 'NULL', T1.trxn_id) = if(T5.acct_trxn_id is null, 'NULL', T5.acct_trxn_id)
这可能是为了加入NULL
s以及正常值。然后它不起作用,因为首先连接条件是T5 ON T1.trxn_id = T5.acct_trxn_id
这意味着NULL没有连接,然后WHERE
在连接后作为过滤器。如果没有连接T5
,那么T5.acct_trxn_id在WHERE中转换为'NULL'字符串,并与NOT NULL T1.trxn_id值进行比较,并且很可能被过滤掉,在这种情况下就像INNER JOIN一样。如果它发生T1.trxn_id是NULL(驱动表),它转换为字符串'NULL'并与always字符串'NULL'进行比较(因为根据ON子句无论如何都没有加入)并且这样的行被传递(我没有测试它虽然)。逻辑看起来很奇怪,我认为它不能按预期工作或转换为INNER。如果要加入包括NULL的所有内容,请将此WHERE移动到JOIN ON子句。
如果有很多行有NULL,那么使用字符串'NULL'替换的NULL连接将使行相乘并导致重复。
实际上在调查JOIN性能不佳时,请检查两件事:
如果一切看起来都很好,那么调整适当的减速器并行度,减少hive.exec.reducers.bytes.per.reducer
以使更多的减速器运行
也尽可能减少DT_LKP
,即使你知道它包含一些绝对不是/不应该是实际表格的日期,如果可能的话使用CTE过滤它。
还可以简化逻辑(这不会提高性能,但会简化代码)。案例在选择中:
when T1.trxn_id is not null and T5.acct_trxn_id is not null and T2.crt_ts >= T5.crt_ts then T2.crt_ts
when T1.trxn_id is not null and T5.acct_trxn_id is not null and T2.crt_ts < T5.crt_ts then T5.crt_ts
<=>
else greatest(T2.trxn_id,T5.crt_ts)
如果T5.crt_ts为null,则case语句将返回null,maximum()也将返回null
row_number中的CASE语句简化:
case when case when (T1.trxn_id is null) or (T5.acct_trxn_id is null) then T2.crt_ts
else greatest(T2.trxn_id,T5.crt_ts)
end
这也是:if(T1.trxn_id is null, 'NULL', T1.trxn_id)
<=> NVL(T1.trxn_id,'NULL')
当然这些只是建议,我没有测试它们