Github user zsxwing commented on the pull request:

    https://github.com/apache/spark/pull/6747#issuecomment-110789261
  
    A simple example of the `conf` command:
    ```Scala
    scala> sqlContext.sql("conf").collect().foreach(v => 
println(v.toSeq.mkString("\t")))
    spark.sql.inMemoryColumnarStorage.batchSize 10000   Controls the size of 
batches for columnar caching.  Larger batch sizes can improve memory 
utilization and compression, but risk OOMs when caching data.
    spark.sql.hive.verifyPartitionPath  true    <TODO>
    spark.sql.retainGroupColumns        true    <TODO>
    spark.sql.codegen   false   When true, code will be dynamically generated 
at runtime for expression evaluation in a specific query. For some queries with 
complicated expression this option can lead to significant speed-ups. However, 
for simple queries this can actually slow down query execution.
    spark.sql.planner.sortMergeJoin     false   <TODO>
    spark.sql.shuffle.partitions        200     Configures the number of 
partitions to use when shuffling data for joins or aggregations.
    spark.sql.planner.externalSort      false   When true, performs sorts 
spilling to disk as needed otherwise sort each partition in memory.
    spark.sql.broadcastTimeout  300     <TODO>
    spark.sql.parquet.filterPushdown    false   Turn on Parquet filter pushdown 
optimization. This feature is turned off by default because of a known bug in 
Paruet 1.6.0rc3 (<a 
href="https://issues.apache.org/jira/browse/PARQUET-136";>PARQUET-136</a>). 
However, if your table doesn't contain any nullable string or binary columns, 
it's still safe to turn this feature on.
    spark.sql.sources.outputCommitterClass      <undefined>     
    spark.sql.parquet.cacheMetadata     true    Turns on caching of Parquet 
schema metadata. Can speed up querying of static data.
    spark.sql.unsafe.enabled    false   <TDDO>
    spark.sql.useSerializer2    true    <TODO>
    ...
    ```


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