Hm, which version of Hadoop are you using? Actually there should also be
a _metadata file together with _common_metadata. I was using Hadoop
2.4.1 btw. I'm not sure whether Hadoop version matters here, but I did
observe cases where Spark behaves differently because of semantic
differences of the same API in different Hadoop versions.
Cheng
On 3/27/15 11:33 AM, Pei-Lun Lee wrote:
Hi Cheng,
on my computer, execute res0.save("xxx",
org.apache.spark.sql.SaveMode.Overwrite) produces:
peilunlee@pllee-mini:~/opt/spark-1.3...rc3-bin-hadoop1$ ls -l xxx
total 32
-rwxrwxrwx 1 peilunlee staff 0 Mar 27 11:29 _SUCCESS*
-rwxrwxrwx 1 peilunlee staff 272 Mar 27 11:29 part-r-00001.parquet*
-rwxrwxrwx 1 peilunlee staff 272 Mar 27 11:29 part-r-00002.parquet*
-rwxrwxrwx 1 peilunlee staff 272 Mar 27 11:29 part-r-00003.parquet*
-rwxrwxrwx 1 peilunlee staff 488 Mar 27 11:29 part-r-00004.parquet*
while res0.save("xxx") produces:
peilunlee@pllee-mini:~/opt/spark-1.3...rc3-bin-hadoop1$ ls -l xxx
total 40
-rwxrwxrwx 1 peilunlee staff 0 Mar 27 11:29 _SUCCESS*
-rwxrwxrwx 1 peilunlee staff 250 Mar 27 11:29 _common_metadata*
-rwxrwxrwx 1 peilunlee staff 272 Mar 27 11:29 part-r-00001.parquet*
-rwxrwxrwx 1 peilunlee staff 272 Mar 27 11:29 part-r-00002.parquet*
-rwxrwxrwx 1 peilunlee staff 272 Mar 27 11:29 part-r-00003.parquet*
-rwxrwxrwx 1 peilunlee staff 488 Mar 27 11:29 part-r-00004.parquet*
On Thu, Mar 26, 2015 at 7:26 PM, Cheng Lian <lian.cs....@gmail.com
<mailto:lian.cs....@gmail.com>> wrote:
I couldn’t reproduce this with the following spark-shell snippet:
|scala> import sqlContext.implicits._
scala> Seq((1, 2)).toDF("a", "b")
scala> res0.save("xxx", org.apache.spark.sql.SaveMode.Overwrite)
scala> res0.save("xxx", org.apache.spark.sql.SaveMode.Overwrite)
|
The _common_metadata file is typically much smaller than
_metadata, because it doesn’t contain row group information, and
thus can be faster to read than _metadata.
Cheng
On 3/26/15 12:48 PM, Pei-Lun Lee wrote:
Hi,
When I save parquet file with SaveMode.Overwrite, it never
generate _common_metadata. Whether it overwrites an existing dir
or not.
Is this expected behavior?
And what is the benefit of _common_metadata? Will reading
performs better when it is present?
Thanks,
--
Pei-Lun
