GitHub user ericl opened a pull request:
https://github.com/apache/spark/pull/17749
[SPARK-20450] [SQL] Unexpected first-query schema inference cost with 2.1.1
## What changes were proposed in this pull request?
https://issues.apache.org/jira/browse/SPARK-19611 fixes a regression from
2.0 where Spark silently fails to read case-sensitive fields missing a
case-sensitive schema in the table properties. The fix is to detect this
situation, infer the schema, and write the case-sensitive schema into the
metastore.
However this can incur an unexpected performance hit the first time such a
problematic table is queried (and there is a high false-positive rate here
since most tables don't actually have case-sensitive fields).
This PR changes the default to NEVER_INFER (same behavior as 2.1.0). In
2.2, we can consider leaving the default to INFER_AND_SAVE.
## How was this patch tested?
Unit tests.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/ericl/spark spark-20450
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/17749.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 #17749
----
commit 4c0ff63044199f59ae25ce887485c16b4b83e663
Author: Eric Liang <e...@databricks.com>
Date: 2017-04-24T19:28:11Z
[SPARK-20450] [SQL] Unexpected first-query schema inference cost with 2.1.1
RC
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