GitHub user seancxmao opened a pull request:
https://github.com/apache/spark/pull/22846
[SPARK-25797][SQL][DOCS] Add migration doc for solving issues caused by
view canonicalization approach change
## What changes were proposed in this pull request?
Since Spark 2.2, view definitions are stored in a different way from prior
versions. This may cause Spark unable to read views created by prior versions.
See [SPARK-25797](https://issues.apache.org/jira/browse/SPARK-25797) for more
details.
Basically, we have 2 options.
1) Make Spark 2.2+ able to get older view definitions back. Since the
expanded text is buggy and unusable, we have to use original text (this is
possible with
[SPARK-25459](https://issues.apache.org/jira/browse/SPARK-25459)). However,
because older Spark versions don't save the context for the database, we cannot
always get correct view definitions without view default database.
2) Recreate the views by `ALTER VIEW AS` or `CREATE OR REPLACE VIEW AS`.
This PR aims to add migration doc to help users troubleshoot this issue by
above option 2.
## How was this patch tested?
N/A.
Docs are generated and checked locally
```
cd docs
SKIP_API=1 jekyll serve --watch
```
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/seancxmao/spark SPARK-25797
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/22846.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 #22846
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commit a6f4d540d948a887d9dd88b5fc83d3dcf065491f
Author: seancxmao <seancxmao@...>
Date: 2018-10-26T06:08:42Z
add migration doc
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