GitHub user hvanhovell opened a pull request:
https://github.com/apache/spark/pull/16843
[SPARK-18609][SPARK-18841][SQL] Fix redundant Alias removal in the
optimizer [Backport-2.1]
This is a backport of
https://github.com/apache/spark/commit/73ee73945e369a862480ef4ac64e55c797bd7d90
## What changes were proposed in this pull request?
The optimizer tries to remove redundant alias only projections from the
query plan using the `RemoveAliasOnlyProject` rule. The current rule identifies
removes such a project and rewrites the project's attributes in the **entire**
tree. This causes problems when parts of the tree are duplicated (for instance
a self join on a temporary view/CTE) and the duplicated part contains the
alias only project, in this case the rewrite will break the tree.
This PR fixes these problems by using a blacklist for attributes that are
not to be moved, and by making sure that attribute remapping is only done for
the parent tree, and not for unrelated parts of the query plan.
The current tree transformation infrastructure works very well if the
transformation at hand requires little or a global contextual information. In
this case we need to know both the attributes that were not to be moved, and we
also needed to know which child attributes were modified. This cannot be done
easily using the current infrastructure, and solutions typically involves
transversing the query plan multiple times (which is super slow). I have moved
around some code in `TreeNode`, `QueryPlan` and `LogicalPlan`to make this much
more straightforward; this basically allows you to manually traverse the tree.
## How was this patch tested?
I have added unit tests to `RemoveRedundantAliasAndProjectSuite` and I have
added integration tests to the `SQLQueryTestSuite.union` and
`SQLQueryTestSuite.cte` test cases.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/hvanhovell/spark SPARK-18609-2.1
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/16843.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 #16843
----
commit 4f0c368b6642d1cfa524cb20de0d1b98e7c35f72
Author: Herman van Hovell <[email protected]>
Date: 2017-02-07T21:28:59Z
[SPARK-18609][SPARK-18841][SQL] Fix redundant Alias removal in the optimizer
This is a backport of
https://github.com/apache/spark/commit/73ee73945e369a862480ef4ac64e55c797bd7d90
## What changes were proposed in this pull request?
The optimizer tries to remove redundant alias only projections from the
query plan using the `RemoveAliasOnlyProject` rule. The current rule identifies
removes such a project and rewrites the project's attributes in the **entire**
tree. This causes problems when parts of the tree are duplicated (for instance
a self join on a temporary view/CTE) and the duplicated part contains the
alias only project, in this case the rewrite will break the tree.
This PR fixes these problems by using a blacklist for attributes that are
not to be moved, and by making sure that attribute remapping is only done for
the parent tree, and not for unrelated parts of the query plan.
The current tree transformation infrastructure works very well if the
transformation at hand requires little or a global contextual information. In
this case we need to know both the attributes that were not to be moved, and we
also needed to know which child attributes were modified. This cannot be done
easily using the current infrastructure, and solutions typically involves
transversing the query plan multiple times (which is super slow). I have moved
around some code in `TreeNode`, `QueryPlan` and `LogicalPlan`to make this much
more straightforward; this basically allows you to manually traverse the tree.
## How was this patch tested?
I have added unit tests to `RemoveRedundantAliasAndProjectSuite` and I have
added integration tests to the `SQLQueryTestSuite.union` and
`SQLQueryTestSuite.cte` test cases.
----
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