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Hive, mail # user - Hive Problems Reading Avro+Snappy Data

Thomas, Matthew 2013-04-07, 21:41
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RE: Hive Problems Reading Avro+Snappy Data
Connell, Chuck 2013-04-07, 23:32
When you do SELECT *, Hive does not run a real MapReduce job, so it is not a good test. Something is wrong with SerDe or InputFormat.

From: Thomas, Matthew [mailto:[EMAIL PROTECTED]]
Sent: Sunday, April 07, 2013 5:41 PM
Subject: Hive Problems Reading Avro+Snappy Data

Hive users,

I am having problems performing "complex" queries on Avro+Snappy data.  If I do a "SELECT * FROM Blah LIMIT 50", I see the data coming back as it should be.  But if I perform any kind of more complex query such as "SELECT count(*) FROM Blah" I am receive several rows of NULL values.  My workflow of how I created the table is described below along with some of the setup.

- I am running CDH4.2 with Avro 1.7.3

hive> select * From mthomas_testavro limit 1;
Field1 Field2
03-19-2013 a
03-19-2013 b
03-19-2013 c
03-19-2013 c
Time taken: 0.103 seconds

hive> select count(*) From mthomas_testavro;
Total MapReduce CPU Time Spent: 6 seconds 420 msec
Time taken: 17.634 seconds
CREATE EXTERNAL TABLE mthomas_testavro
LOCATION '/tmp/testavro/'
"namespace": "hello.world",
"name": "some_schema",
"type": "record",
"fields": [
{ "name":"field1","type":"string"},
{ "name":"field2","type":"string"}

SET avro.output.codec=snappy;
SET mapred.output.compression.type=BLOCK;
SET hive.exec.compress.output=true;
SET mapred.map.output.compression.codec=org.apache.hadoop.io.compress.SnappyCodec;
SET mapred.output.compression.codec=org.apache.hadoop.io.compress.SnappyCodec;

INSERT OVERWRITE TABLE mthomas_testavro SELECT * FROM identical_table_inGzip_format;

If I cat the output file in the external table, I see "Objavro.codec^Lsnappyavro.schema?{"type"..." at the beginning followed by the rest of the schema and binary data.  So I am assuming the snappy compression worked.  Furthermore, I also tried to query this table via Impala and both queries worked just fine.

Maybe it is related to https://issues.apache.org/jira/browse/HIVE-3308  ???

Any ideas?


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Thomas, Matthew 2013-04-08, 11:58
Bennie Schut 2013-04-08, 12:18