GitHub user ianluyan opened a pull request:
https://github.com/apache/spark/pull/4394
[SPARK-5614][SQL] Predicate pushdown through Generate.
Now in Catalyst's rules, predicates can not be pushed through "Generate"
nodes. Further more, partition pruning in HiveTableScan can not be applied on
those queries involves "Generate". This makes such queries very inefficient. In
practice, it finds patterns like
```scala
Filter(predicate, Generate(generator, _, _, _, grandChild))
```
and splits the predicate into 2 parts by referencing the generated column
from Generate node or not. And a new Filter will be created for those conjuncts
can be pushed beneath Generate node. If nothing left for the original Filter,
it will be removed.
For example, physical plan for query
```sql
select len, bk
from s_server lateral view explode(len_arr) len_table as len
where len > 5 and day = '20150102';
```
where 'day' is a partition column in metastore is like this in current
version of Spark SQL:
> Project [len, bk]
>
> Filter ((len > "5") && "(day = "20150102")")
>
> Generate explode(len_arr), true, false
>
> HiveTableScan [bk, len_arr, day], (MetastoreRelation default, s_server,
None), None
But theoretically the plan should be like this
> Project [len, bk]
>
> Filter (len > "5")
>
> Generate explode(len_arr), true, false
>
> HiveTableScan [bk, len_arr, day], (MetastoreRelation default, s_server,
None), Some(day = "20150102")
Where partition pruning predicates can be pushed to HiveTableScan nodes.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/ianluyan/spark ppd
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/4394.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #4394
----
commit d312f20fb00faeda2f0a207fad75555896102e05
Author: Lu Yan <[email protected]>
Date: 2015-02-05T11:13:39Z
[SPARK-5614][SQL] Predicate pushdown through Generate.
With this patch, queries involves 'explode' can benefit from predicate
pushdown, thus partition pruning.
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