CellUtil: Key type in createCell method

Question

I am using the CellUtil class packaged in org.apache.hadoop.hbase to create a Cell object. The function header looks like this:

public static Cell createCell(byte[] row, byte[] family, byte[] qualifier, long timestamp, byte type, byte[] value)

What does the 5th. argument byte type represent? I looked into the KeyValueType class and it refers to an enum called Type with the following definition:

public static enum Type {
Minimum((byte)0),
Put((byte)4),

Delete((byte)8),
DeleteFamilyVersion((byte)10),
DeleteColumn((byte)12),
DeleteFamily((byte)14),

// Maximum is used when searching; you look from maximum on down.
Maximum((byte)255);

private final byte code;

Type(final byte c) {
  this.code = c;
}

public byte getCode() {
  return this.code;
}

My question is, what has the type minimum, put, etc. got to do with the type of cell I want to create?

Answer 1

Sarin, Please refer 69.7.6. KeyValue

There are some scenarios in which you will use these enums. For Example, I'm writing coprocessor like below then I will use KeyValue.Type.Put.getCode() similarly other Enums also can be used like this. See example co-processor usage below...

package getObserver;

import java.io.IOException;
import java.util.List;
import java.util.NavigableSet;

import org.apache.hadoop.hbase.Cell;
import org.apache.hadoop.hbase.CellUtil;
import org.apache.hadoop.hbase.KeyValue;
import org.apache.hadoop.hbase.client.Get;
import org.apache.hadoop.hbase.coprocessor.BaseRegionObserver;
import org.apache.hadoop.hbase.coprocessor.ObserverContext;
import org.apache.hadoop.hbase.coprocessor.RegionCoprocessorEnvironment;

public class Observer extends BaseRegionObserver{

    private boolean isOewc;

    @Override
    public void preGetOp(ObserverContext<RegionCoprocessorEnvironment> arg0,
            Get arg1, List<Cell> arg2) throws IOException {
        NavigableSet<byte[]> qset = arg1.getFamilyMap().get("colfam1".getBytes());
        if(qset==null){//do nothing

        }else{

            String message = "qset.size() = "+String.valueOf(qset.size());
            String m = "isOewc = "+String.valueOf(isOewc);
            this.isOewc = true;
            Cell cell = CellUtil.createCell(
                    "preGet Row".getBytes(), 
                    m.getBytes(), 
                    message.getBytes(), 
                    System.currentTimeMillis(), 
                    KeyValue.Type.Put.getCode(), 
                    "preGet Value".getBytes());
            arg2.add(cell);
        }
    }

    @Override
    public void postGetOp(ObserverContext<RegionCoprocessorEnvironment> arg0,
            Get arg1, List<Cell> arg2) throws IOException {
        String m = "isOewc = "+String.valueOf(isOewc);
        Cell cell = CellUtil.createCell(
                "postGet Row".getBytes(), 
                m.getBytes(), 
                "postGet Qualifier".getBytes(), 
                System.currentTimeMillis(), 
                KeyValue.Type.Put.getCode(), 
                "postGet Value".getBytes());
        arg2.add(cell);
    }
}

Similarly other below EnumTypes can be used if you don't know which operation you are going to perform on co-processor event..

programcreek examples clearly explains what is the usage of Put,Delete(prepare key value pairs for mutation) maximum,minimum (for range check). also Co-processor above example uses Put.