question Re: HiveContext is not reading schema of an Orcfile in Support Questions

HiveContext is not reading schema of an Orcfile

jay_ch — Wed, 03 Aug 2016 02:26:34 GMT

When I run the following:

<code>val df1 = sqlContext.read.format("orc").load(myPath)
df1.columns.map(m => println(m))

The columns are printed as '_col0', '_col1', '_col2' etc. As opposed to their real names such as 'empno', 'name', 'deptno'.

When I 'describe mytable' in Hive it prints the column name correctly, but when I run 'orcfiledump' it shows _col0, _col1, _col2 as well. Do I have to specify 'schema on read' or something? If yes, how do I do that in Spark/Scala?

<code>hive --orcfiledump /apps/hive/warehouse/mydb.db/mytable1
.....
fieldNames:"_col0"
fieldNames:"_col1"
fieldNames:"_col2"

As suggested elsewhere I've added '--files' BEFORE '--jars' as follows:

spark-submit \
  --master yarn \
  --deploy-mode cluster \
  --class xxx.xxxx.MyDriver \
  --files hive-site.xml \
  --jars datanucleus-api-jdo-3.2.6.jar,datanucleus-core-3.2.10.jar,datanucleus-rdbms-3.2.9.jar \
  --name MyDriver \
  --num-executors 1 \
  --driver-memory 1g \
  --executor-memory 1g \
  --executor-cores 1 \
   ./my-utils-1.0-SNAPSHOT.jar

Note: I created the table as follows:

<code>create table mydb.mytable1 (empno int, name VARCHAR(20), deptno int) stored as orc;

Note: This is not a duplicate of this issue (Hadoop ORC file - How it works - How to fetch metadata) because the answer tells me to use 'Hive' & I am already using HiveContext as follows:

<code>val sqlContext =new org.apache.spark.sql.hive.HiveContext(sc)

By the way, I am using my own hive-site.xml, which contains following:

<code><configuration>
  <property>
    <name>hive.metastore.uris</name>
    <value>thrift://sandbox.hortonworks.com:9083</value>
  </property>
</configuration>

Re: HiveContext is not reading schema of an Orcfile

RyanCicak — Wed, 03 Aug 2016 04:50:10 GMT

Hi @Jay Ch

Great question. You must register your df1 as a temporary table like:

val table = sqlContext.read.format("orc").load("/apps/hive/warehouse/yourtable")

table.registerTempTable("yourtable")

and then run:

val tester = sqlContext.sql("select * from yourtable");

tester.columns

You'll get the actual column names

Re: HiveContext is not reading schema of an Orcfile

jay_ch — Wed, 03 Aug 2016 06:48:19 GMT

Not sure I understand the answer. I need to run "select * from yourtable" to get column names populated? Perhaps "select * from yourtable limit 1". I can try this, but shouldn't the column names be populated from Metastore as soon as I do a 'load'?

Re: HiveContext is not reading schema of an Orcfile

jay_ch — Wed, 03 Aug 2016 09:21:41 GMT

Tried it but it doesn't work. Columns are still '_col0', '_col1', '_col2'

Re: HiveContext is not reading schema of an Orcfile

jay_ch — Thu, 04 Aug 2016 04:35:15 GMT

I figured out what the problem was. It was the way I was creating the test data. I was under the impression that if I run the following commands:

create table mydb.mytable1 (empno int, name VARCHAR(20), deptno int) stored as orc;

INSERT INTO mydb.mytable1(empno, name, deptno) VALUES (1, 'EMP1',100);
INSERT INTO mydb.mytable1(empno, name, deptno) VALUES (2, 'EMP2',50);
INSERT INTO mydb.mytable1(empno, name, deptno) VALUES (3, 'EMP3',200);

Data would be created in the ORC format at: /apps/hive/warehouse/mydb.db/mytable1

Turns out that's not the case. Even though I indicated 'stored as orc' the INSERT statements didn't save the column information. Not sure if that's expected behavior. In any case, it all works now. Apologies for the confusion but hopefully this will help someone in future -:)

Re: HiveContext is not reading schema of an Orcfile

talktojulio — Tue, 24 Jan 2017 02:42:01 GMT

I am with the same issue

I have the same isssue.

Re: HiveContext is not reading schema of an Orcfile

tenke_iu8 — Wed, 01 Mar 2017 22:41:34 GMT

Hi,

You should use val df = hiveContext.read.table("table_name") instead. In this case, columns are displayed properly.