Re: How to use DBInputFormat?

Thu, 05 Feb 2009 06:29:03 -0800 

Indeed sir.
The implementation was designed like you describe for two reasons. First and foremost to make is as simple as possible for the user to use a JDBC database as input and output for Hadoop. Secondly because of the specific requirements the MapReduce framework brings to the table (split distribution, split reproducibility etc). 


This design will, as you note, never handle the same amount of data as  
HBase (or HDFS), and was never intended to. That being said, there are  
a couple of ways that the current design could be augmented to perform  
better (and, as in its current form, tweaked, depending on you data  
and computational requirements). Shard awareness is one way, which  
would let each database/tasktracker-node execute mappers on data where  
each split is a single database server for example.



If you have any ideas on how the current design can be improved,  
please do share.



Fredrik

On Feb 5, 2009, at 11:37 AM, Stefan Podkowinski wrote:


The 0.19 DBInputFormat class implementation is IMHO only suitable for
very simple queries working on only few datasets. Thats due to the
fact that it tries to create splits from the query by
1) getting a count of all rows using the specified count query (huge
performance impact on large tables)
2) creating splits by issuing an individual query for each split with
a "limit" and "offset" parameter appended to the input sql query

Effectively your input query "select * from orders" would become
"select * from orders limit <splitlength> offset <splitstart>" and
executed until count has been reached. I guess this is not working sql
syntax for oracle.

Stefan


2009/2/4 Amandeep Khurana <[email protected]>:

Adding a semicolon gives me the error "ORA-00911: Invalid character"

Amandeep


Amandeep Khurana
Computer Science Graduate Student
University of California, Santa Cruz



On Wed, Feb 4, 2009 at 6:46 AM, Rasit OZDAS <[email protected]>  
wrote:



Amandeep,
"SQL command not properly ended"
I get this error whenever I forget the semicolon at the end.
I know, it doesn't make sense, but I recommend giving it a try

Rasit

2009/2/4 Amandeep Khurana <[email protected]>:

The same query is working if I write a simple JDBC client and  
query the

database. So, I'm probably doing something wrong in the connection

settings.

But the error looks to be on the query side more than the  
connection

side.


Amandeep


Amandeep Khurana
Computer Science Graduate Student
University of California, Santa Cruz


On Tue, Feb 3, 2009 at 7:25 PM, Amandeep Khurana <[email protected]>

wrote:



Thanks Kevin

I couldnt get it work. Here's the error I get:

bin/hadoop jar ~/dbload.jar LoadTable1

09/02/03 19:21:17 INFO jvm.JvmMetrics: Initializing JVM Metrics  
with

processName=JobTracker, sessionId=

09/02/03 19:21:20 INFO mapred.JobClient: Running job:  
job_local_0001

09/02/03 19:21:21 INFO mapred.JobClient:  map 0% reduce 0%
09/02/03 19:21:22 INFO mapred.MapTask: numReduceTasks: 0
09/02/03 19:21:24 WARN mapred.LocalJobRunner: job_local_0001
java.io.IOException: ORA-00933: SQL command not properly ended

       at


org 
.apache 
.hadoop 
.mapred.lib.db.DBInputFormat.getRecordReader(DBInputFormat.java:289)

       at org.apache.hadoop.mapred.MapTask.run(MapTask.java:321)
       at

org.apache.hadoop.mapred.LocalJobRunner 
$Job.run(LocalJobRunner.java:138)

java.io.IOException: Job failed!
       at

org.apache.hadoop.mapred.JobClient.runJob(JobClient.java:1217)

       at LoadTable1.run(LoadTable1.java:130)

       at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java: 
65)
       at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java: 
79)

       at LoadTable1.main(LoadTable1.java:107)

       at sun.reflect.NativeMethodAccessorImpl.invoke0(Native  
Method)
       at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown  
Source)

       at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown

Source)

       at java.lang.reflect.Method.invoke(Unknown Source)
       at org.apache.hadoop.util.RunJar.main(RunJar.java:165)
       at org.apache.hadoop.mapred.JobShell.run(JobShell.java:54)

       at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java: 
65)
       at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java: 
79)

       at org.apache.hadoop.mapred.JobShell.main(JobShell.java:68)

Exception closing file


/user/amkhuran/contract_table/_temporary/ 
_attempt_local_0001_m_000000_0/part-00000

java.io.IOException: Filesystem closed
       at

org.apache.hadoop.hdfs.DFSClient.checkOpen(DFSClient.java:198)

       at

org.apache.hadoop.hdfs.DFSClient.access$600(DFSClient.java:65)

       at


org.apache.hadoop.hdfs.DFSClient 
$DFSOutputStream.closeInternal(DFSClient.java:3084)

       at


org.apache.hadoop.hdfs.DFSClient 
$DFSOutputStream.close(DFSClient.java:3053)

       at

org.apache.hadoop.hdfs.DFSClient 
$LeaseChecker.close(DFSClient.java:942)
       at org.apache.hadoop.hdfs.DFSClient.close(DFSClient.java: 
210)

       at


org 
.apache 
.hadoop 
.hdfs.DistributedFileSystem.close(DistributedFileSystem.java:243)

       at

org.apache.hadoop.fs.FileSystem$Cache.closeAll(FileSystem.java: 
1413)
       at  
org.apache.hadoop.fs.FileSystem.closeAll(FileSystem.java:236)

       at

org.apache.hadoop.fs.FileSystem 
$ClientFinalizer.run(FileSystem.java:221)



Here's my code:

public class LoadTable1 extends Configured implements Tool  {

     // data destination on hdfs
     private static final String CONTRACT_OUTPUT_PATH =

"contract_table";


     // The JDBC connection URL and driver implementation class


private static final String CONNECT_URL =  
"jdbc:oracle:thin:@dbhost

:1521:PSEDEV";
     private static final String DB_USER = "user";
     private static final String DB_PWD = "pass";
     private static final String DATABASE_DRIVER_CLASS =
"oracle.jdbc.driver.OracleDriver";

     private static final String CONTRACT_INPUT_TABLE =
"OSE_EPR_CONTRACT";


     private static final String [] CONTRACT_INPUT_TABLE_FIELDS  
= {

       "PORTFOLIO_NUMBER", "CONTRACT_NUMBER"};

     private static final String ORDER_CONTRACT_BY_COL =
"CONTRACT_NUMBER";


   static class ose_epr_contract implements Writable, DBWritable {


       String CONTRACT_NUMBER;


       public void readFields(DataInput in) throws IOException {

           this.CONTRACT_NUMBER = Text.readString(in);

       }

       public void write(DataOutput out) throws IOException {

           Text.writeString(out, this.CONTRACT_NUMBER);


       }


       public void readFields(ResultSet in_set) throws  
SQLException {


           this.CONTRACT_NUMBER = in_set.getString(1);

       }

       @Override

       public void write(PreparedStatement prep_st) throws  
SQLException

{

           // TODO Auto-generated method stub

       }

   }

   public static class LoadMapper extends MapReduceBase
                               implements Mapper<LongWritable,
ose_epr_contract, Text, NullWritable> {
       private static final char FIELD_SEPARATOR = 1;

       public void map(LongWritable arg0, ose_epr_contract arg1,

               OutputCollector<Text, NullWritable> arg2,  
Reporter arg3)

               throws IOException {

           StringBuilder sb = new StringBuilder();
;
           sb.append(arg1.CONTRACT_NUMBER);



           arg2.collect(new Text (sb.toString()),  
NullWritable.get());


       }

   }


   public static void main(String[] args) throws Exception {
       Class.forName("oracle.jdbc.driver.OracleDriver");
       int exit = ToolRunner.run(new LoadTable1(), args);

   }

   public int run(String[] arg0) throws Exception {
       JobConf conf = new JobConf(getConf(), LoadTable1.class);

       conf.setInputFormat(DBInputFormat.class);
       DBConfiguration.configureDB(conf, DATABASE_DRIVER_CLASS,
CONNECT_URL, DB_USER, DB_PWD);

       DBInputFormat.setInput(conf, ose_epr_contract.class,
               "select CONTRACT_NUMBER from OSE_EPR_CONTRACT",

               "select COUNT(CONTRACT_NUMBER) from  
OSE_EPR_CONTRACT");

       FileOutputFormat.setOutputPath(conf, new
Path(CONTRACT_OUTPUT_PATH));

       conf.setMapperClass(LoadMapper.class);
       conf.setNumReduceTasks(0);

       conf.setOutputKeyClass(Text.class);
       conf.setOutputValueClass(NullWritable.class);

       JobClient.runJob(conf);

       return 0;
   }
}

-Amandeep

Amandeep Khurana
Computer Science Graduate Student
University of California, Santa Cruz


On Tue, Feb 3, 2009 at 6:51 PM, Kevin Peterson <[email protected]

wrote:



On Tue, Feb 3, 2009 at 5:49 PM, Amandeep Khurana <[email protected] 
>

wrote:


In the setInput(...) function in DBInputFormat, there are two  
sets of

arguments that one can use.

1. public static void *setInput*(JobConf


a) In this, do we necessarily have to give all the fieldNames  
(which

are

the

column names right?) that the table has, or do we need to  
specify

only

the

ones that we want to extract?



You may specify only those columns that you are interested in.


b) Do we have to have a orderBy or not necessarily? Does this  
relate to

the

primary key in the table in any ways?



Conditions and order by are not necessary.


a) Is there any restriction on the kind of queries that this  
function

can take in the inputQuery string?



I don't think so, but I don't use this method -- I just use the

fieldNames

and tableName method.



I am facing issues in getting this to work with an Oracle  
database

and

have no idea of how to debug it (an email sent earlier).
Can anyone give me some inputs on this please?




Create a new table that has one column, put about five entries  
into

that

table, then try to get a map job working that outputs the  
values to a

text

file. If that doesn't work, post your code and errors.










--
M. Raşit ÖZDAŞ



























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