HyukjinKwon opened a new pull request #28459:
URL: https://github.com/apache/spark/pull/28459
### What changes were proposed in this pull request?
This PR proposes to deprecate 'spark.sql.optimizer.metadataOnly'
configuration and remove it in the future release.
### Why are the changes needed?
This optimization can cause a potential correctness issue, see also
SPARK-26709.
Also, it seems difficult to extend the optimization. Basically you should
whitelist all available functions. It costs some maintenance overhead, see also
SPARK-31590.
Looks we should just better let users use `SparkSessionExtensions` instead
if they must use, and remove it in Spark side.
### Does this PR introduce _any_ user-facing change?
Yes, setting `spark.sql.optimizer.metadataOnly` will shod a deprecation
warning:
```scala
scala> spark.conf.unset("spark.sql.optimizer.metadataOnly")
```
```
20/05/06 12:57:23 WARN SQLConf: The SQL config
'spark.sql.optimizer.metadataOnly' has been
deprecated in Spark v3.0 and may be removed in the future. Avoid to depend
on this optimization
to prevent a potential correctness issue. If you must use, use
'SparkSessionExtensions' instead to
inject it as a custom rule.
```
```scala
scala> spark.conf.set("spark.sql.optimizer.metadataOnly", "true")
```
```
20/05/06 12:57:44 WARN SQLConf: The SQL config
'spark.sql.optimizer.metadataOnly' has been
deprecated in Spark v3.0 and may be removed in the future. Avoid to depend
on this optimization
to prevent a potential correctness issue.If you must use, use
'SparkSessionExtensions' instead to
inject it as a custom rule.
```
### How was this patch tested?
Manually tested.
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