Monitoring bytes read per cf

[Daniel Doubleday]

Hi all

got a question for folks with some code insight again.

To be able to better understand where our IO load is coming from we want to 
monitor the number of bytes read from disc per cf. (we love stats)

What I have done is wrapping the FileDataInput in SSTableReader to sum the 
bytes read in CFS. This will only record data file access but that would be 
good enough for us.

It seems to work fine but maybe someone here knows that this is not a good idea 
....

Cheers,
Daniel

Some code:

SSTableReader:
    private static final boolean KEEP_IO_STATISICS = 
Boolean.getBoolean("cassandra.keepIOStats");
    public FileDataInput getFileDataInput(DecoratedKey decoratedKey, int 
bufferSize)
    {
        long position = getPosition(decoratedKey, Operator.EQ);
        if (position < 0)
            return null;

        FileDataInput segment = dfile.getSegment(position, bufferSize);
        return (KEEP_IO_STATISICS) ? new MonitoringFileDataIInput(metadata, 
segment) : segment; 
    }

with MonitoringFileDataIInput

public class MonitoringFileDataIInput implements FileDataInput, Closeable
{

    private final FileDataInput fileDataInput;
    private final ColumnFamilyStore columnFamilyStore;

    public MonitoringFileDataIInput(CFMetaData cfMetaData, FileDataInput 
fileDataInput)
    {
        columnFamilyStore = 
Table.open(cfMetaData.tableName).getColumnFamilyStore(cfMetaData.cfId);
        this.fileDataInput = fileDataInput;
    }

    @Override
    public boolean readBoolean() throws IOException
    {
        columnFamilyStore.addBytesRead(1);
        return fileDataInput.readBoolean();        
    }

    // ... etc

and ColumnFamilyStore
    private final AtomicLong bytesRead = new AtomicLong(0L);
    
    @Override // ColumnFamilyStoreMBean
    public long getBytesRead()
    {
        return bytesRead.get();
    }
    
    public void addBytesRead(int num) 
    {
        bytesRead.addAndGet(num);
    }