Hi Avrilia Is it a partitioned table? If so approximately how many partitions are there and how many files are there? What is the value for hive.input.format?
My suspicion is that there are ~180 files and each file is ~515MB in size. Since, you had mentioned you are using default stripe size i.e, 256MB, the default HDFS block size for ORC files will be chose as 512MB. When a query is issued, the input files are split on HDFS block boundaries. So if the file size in a partition is 515MB there will be 2 splits per file (512MB on HDFS block boundary + remaining 3MB). This happens when the input format is set to HiveInputFormat. Thanks Prasanth Jayachandran On Feb 10, 2014, at 12:49 AM, Avrilia Floratou <avrilia.flora...@gmail.com> wrote: > Hi all, > > I'm running a query that scans a file stored in ORC format and extracts some > columns. My file is about 92 GB, uncompressed. I kept the default stripe > size. The MapReduce job generates 363 map tasks. > > I have noticed that the first 180 map tasks finish in 3 secs (each) and after > they complete the HDFS_BYTES_READ counter is equal to about 3MB. Then the > remaining map tasks are the ones that scan the data and each one completes in > about 20 sec. It seems that each of these map tasks gets as input 512 MB of > the file. I was wondering, what exactly are the first short map tasks doing? > > Thanks, > Avrilia -- CONFIDENTIALITY NOTICE NOTICE: This message is intended for the use of the individual or entity to which it is addressed and may contain information that is confidential, privileged and exempt from disclosure under applicable law. If the reader of this message is not the intended recipient, you are hereby notified that any printing, copying, dissemination, distribution, disclosure or forwarding of this communication is strictly prohibited. If you have received this communication in error, please contact the sender immediately and delete it from your system. Thank You.
