Thanks Ted - That makes sense .. If I want the mapper to pass around a
custom object as Key .. I need to provide the compareTo method = implement
WritableComparable instead of Writable .. I did that and map stage is
working fine now .. reducer is throwing an error now .. I am assuming its
not able to communicate with database since its an IO exception but it
doesnt provides much useful information ..
11/02/06 17:26:51 INFO mapred.JobClient: Task Id :
attempt_201102061204_0004_r_000000_0, Status : FAILED
java.io.IOException
at
org.apache.hadoop.mapreduce.lib.db.DBOutputFormat.getRecordWriter(DBOutputFormat.java:180)
at
org.apache.hadoop.mapred.ReduceTask.runNewReducer(ReduceTask.java:557)
at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:412)
at org.apache.hadoop.mapred.Child$4.run(Child.java:217)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:396)
at
org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1063)
at org.apache.hadoop.mapred.Child.main(Child.java:211)
On Sun, Feb 6, 2011 at 11:00 AM, Ted Yu <[email protected]> wrote:
> I think you have looked at
> src/examples/org/apache/hadoop/examples/DBCountPageView.java
> where:
> job.setMapOutputKeyClass(Text.class);
>
> and:
> public class Text extends BinaryComparable
> implements WritableComparable<BinaryComparable> {
> ...
> static {
> // register this comparator
> WritableComparator.define(Text.class, new Comparator());
> }
>
> Modify your LogRecord accordingly.
>
> On Fri, Feb 4, 2011 at 12:00 PM, Adeel Qureshi <[email protected]
> >wrote:
>
> > Thanks - I switched to using the mapreduce version of dboutputformat and
> > things look a little better but I am getting a ClassCastException ..
> >
> > here is my writable class
> > public class LogRecord implements Writable, DBWritable {
> > private long timestamp;
> > private String userId;
> > private String action;
> >
> > public LogRecord() {
> > }
> >
> > public LogRecord(long timestamp, String userId, String action,
> > String pageType, String pageName, String attrPath, String
> > attrName,
> > String forEntity, String forEntityInfo, long rendTime) {
> > this.timestamp = timestamp;
> > this.userId = userId;
> > this.action = action;
> > }
> >
> > public void clearFields(){
> > this.timestamp = 0;
> > this.userId = "";
> > this.action = "";
> > }
> >
> > @Override
> > public int hashCode() {
> > final int prime = 31;
> > int result = 1;
> > result = prime * result + ((action == null) ? 0 :
> > action.hashCode());
> > result = prime * result + (int) (timestamp ^ (timestamp >>> 32));
> > result = prime * result + ((userId == null) ? 0 :
> > userId.hashCode());
> > return result;
> > }
> >
> > @Override
> > public boolean equals(Object obj) {
> > if (this == obj)
> > return true;
> > if (obj == null)
> > return false;
> > if (getClass() != obj.getClass())
> > return false;
> > LogRecord other = (LogRecord) obj;
> > if (action == null) {
> > if (other.action != null)
> > return false;
> > } else if (!action.equals(other.action))
> > return false;
> > if (timestamp != other.timestamp)
> > return false;
> > if (userId == null) {
> > if (other.userId != null)
> > return false;
> > } else if (!userId.equals(other.userId))
> > return false;
> > return true;
> > }
> >
> > @Override
> > public void readFields(DataInput in) throws IOException {
> > this.timestamp = in.readLong();
> > this.userId = Text.readString(in);
> > this.action = Text.readString(in);
> > }
> >
> > @Override
> > public void write(DataOutput out) throws IOException {
> > out.writeLong(this.timestamp);
> > Text.writeString(out, this.userId);
> > Text.writeString(out, this.action);
> > }
> >
> > @Override
> > public void readFields(ResultSet rs) throws SQLException {
> > this.timestamp = rs.getLong(1);
> > this.userId = rs.getString(2);
> > this.action = rs.getString(3);
> > }
> >
> > @Override
> > public void write(PreparedStatement stmt) throws SQLException {
> > stmt.setLong(1, this.timestamp);
> > stmt.setString(2, this.userId);
> > stmt.setString(3, this.action);
> > }
> >
> > public void setTimestamp(long timestamp) {
> > this.timestamp = timestamp;
> > }
> > public void setUserId(String userId) {
> > this.userId = userId;
> > }
> > public void setAction(String action) {
> > this.action = action;
> > }
> > }
> > **************************************
> >
> > here is my job runner/configuration code
> >
> > //configuration
> > Configuration conf = new Configuration();
> > Job job = new Job(conf, "Log Parser Job");
> >
> > //configure database output
> > job.setOutputFormatClass(DBOutputFormat.class);
> > DBConfiguration.configureDB(conf,
> > "com.microsoft.sqlserver.jdbc.SQLServerDriver",
> > "jdbc:sqlserver://..........",
> > "...", "...");
> > String[] fields = {"timestamp", "userId", "action"};
> > DBOutputFormat.setOutput(job, "LogParser", fields);
> >
> > //job properties
> > job.setJarByClass(Driver.class);
> >
> > job.setMapperClass(LogParserMapper.class);
> > job.setReducerClass(LogParserReducer.class);
> >
> > job.setMapOutputKeyClass(LogRecord.class);
> > job.setMapOutputValueClass(IntWritable.class);
> >
> > job.setOutputKeyClass(LogRecord.class);
> > job.setOutputValueClass(NullWritable.class);
> >
> > *************
> >
> > mapper code:
> > public class LogParserMapper extends Mapper<LongWritable, Text,
> LogRecord,
> > IntWritable> {
> >
> > private LogRecord rec = new LogRecord();
> > private final static IntWritable _val = new IntWritable(1);
> >
> > public void map(LongWritable key, Text value, Context context){
> > String line = value.toString();
> > //parse the line into tokens
> > ...
> > rec.setUserId(userId);
> > rec.setAction("test");
> > rec.setTimestamp(0);
> > }
> > }
> >
> > ******************
> > reducer:
> >
> > public class LogParserReducer extends Reducer<LogRecord, IntWritable,
> > LogRecord, NullWritable> {
> > private NullWritable n = NullWritable.get();
> >
> > public void reduce(LogRecord key, Iterable<IntWritable> values,
> Context
> > context) throws IOException, InterruptedException {
> > context.write(key, n);
> > }
> > }
> >
> > ******************
> > finally when i run it I am getting this error message
> >
> > 11/02/04 13:47:55 INFO mapred.JobClient: Task Id :
> > attempt_201101241250_0094_m_000000_1, Status : FAILED
> > java.lang.ClassCastException: class logparser.model.LogRecord
> > at java.lang.Class.asSubclass(Class.java:3018)
> > at
> > org.apache.hadoop.mapred.JobConf.getOutputKeyComparator(JobConf.java:796)
> > at
> > org.apache.hadoop.mapred.MapTask$MapOutputBuffer.<init>(MapTask.java:809)
> > at
> >
> >
> org.apache.hadoop.mapred.MapTask$NewOutputCollector.<init>(MapTask.java:549)
> > at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:631)
> > at org.apache.hadoop.mapred.MapTask.run(MapTask.java:315)
> > at org.apache.hadoop.mapred.Child$4.run(Child.java:217)
> > at java.security.AccessController.doPrivileged(Native Method)
> > at javax.security.auth.Subject.doAs(Subject.java:396)
> > at
> >
> >
> org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1063)
> > at org.apache.hadoop.mapred.Child.main(Child.java:211)
> >
> >
> > my hadoop version is 0.20.2 so I am not sure why its using the mapred
> stuff
> > while running it and if thats the problem.
> >
> > Thanks for your help
> >
> >
> > On Thu, Feb 3, 2011 at 9:29 PM, Ted Yu <[email protected]> wrote:
> >
> > > At least in cdh3b2, there are two DBOutputFormat.java:
> > >
> > > ./src/mapred/org/apache/hadoop/mapred/lib/db/DBOutputFormat.java
> > > ./src/mapred/org/apache/hadoop/mapreduce/lib/db/DBOutputFormat.java
> > >
> > > You should be able to use the latter.
> > >
> > > On Thu, Feb 3, 2011 at 2:45 PM, Adeel Qureshi <[email protected]
> > > >wrote:
> > >
> > > > I had started a thread recently to ask questions about custom
> writable
> > > > implementations which is basically similar to this .. but that was
> more
> > > of
> > > > an understanding of the concept and here I wanted to ask my actual
> > > problem
> > > > and get help on that.
> > > >
> > > > I want to be able to read text data line by line in my mapper ..
> > > > create an instance of a custom writable class that holds some
> > information
> > > > parsed out of the line ..
> > > > pass that custom writable along with its count to reducer
> > > > reducer then simply need to insert every single entry into a database
> > ..
> > > >
> > > > I am just trying to understand how to accomplish this. here is what I
> > am
> > > > thinking i need to do based on my little understanding of all this
> > custom
> > > > stuff
> > > >
> > > > 1. create a custom writable class that can hold my parsed records. in
> > my
> > > > mapper create a new instance of it using the text line and output the
> > > > created instance
> > > > 2. accept this custom writable in mapper
> > > > 3. set reducer output to DBOutputFormat
> > > > I tried doing that and it seems like I am supposed to use JobConf
> > > class
> > > > which is deprecated and the new configuration class where you are
> > > supposed
> > > > to use the job object to set the input/output formats doesnt seems to
> > > work
> > > > with DBOuputFormat .. doesnt this DBOutputFormat stuff works with
> > hadoop
> > > > new
> > > > api
> > > >
> > > > 4. now in reducer I am confused wat to do .. i guess i need to
> convert
> > my
> > > > custom writable object to another custom dbwritable object .. that
> will
> > > > then
> > > > be written to the database .. any hints on how to accomplish this ..
> > > >
> > > > Sorry if the questions arent very clear .. I am just really confused
> > > about
> > > > this stuff and it doesnt helps that there is literally NO useful
> > > > information
> > > > available anywhere on this writable and dbwritable stuff
> > > >
> > > > Thanks
> > > > Adeel
> > > >
> > >
> >
>
