All Known Implementing Classes:

MergeByteBuffer, MergeGenericRecord
```
public interface Merge<T>
```
API for merging existing data with incoming writes. There should be at least one implementation of this interface for each version of the replication metadata protocol, and possibly more if multiple competing implementations are created in an attempt to optimize performance, efficiency or other considerations. Conceptually, the various functions merge together 4 elements relating to a given key in the store: 1. The old value associated with the key 2. The old replication metadata associated with the old value 3. The incoming write operation for that key (absent in case of deletes) 4. The timestamp of the write operation Conflict resolution rules must be applied deterministically such that given an old value and an old replication metadata, a set of write operations (and their associated timestamp) may be applied in any order and always converge to the same end result (i.e. to the same final value and replication metadata). This determinism is achieved by the following rules: 1. The fields which are set in the write operation will clobber those of the old value if and only if the write operation timestamp is greater than the timestamp associated with that field in the replication metadata. 2. Each element included in a collection merging operation is applied to the corresponding collection in the old value iif the write operation timestamp is greater than the timestamp of the corresponding element, than the timestamp of the corresponding element's tombstone, and than the collection's timestamp. 3. In case of equal timestamps, the value of the field or of the element is compared to that of the old field or element in order to deterministically decide which one wins the conflict resolution. Note: all implementation must return the reference of the same ValueAndRmd instance that was passed in. The input ValueAndRmd object may be mutated or replaced its inner variables. As such, a caller of this function should not expect the passed in parameter to remain unchanged.

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`ValueAndRmd<T>`	`delete(ValueAndRmd<T> oldValueAndRmd, long deleteOperationTimestamp, int deleteOperationColoID, long newValueSourceOffset, int newValueSourceBrokerID)`
`ValueAndRmd<T>`	`put(ValueAndRmd<T> oldValueAndRmd, T newValue, long putOperationTimestamp, int putOperationColoID, long newValueSourceOffset, int newValueSourceBrokerID)`
`ValueAndRmd<T>`	`update(ValueAndRmd<T> oldValueAndRmd, Lazy<org.apache.avro.generic.GenericRecord> writeOperation, org.apache.avro.Schema currValueSchema, long updateOperationTimestamp, int updateOperationColoID, long newValueSourceOffset, int newValueSourceBrokerID)`

- Method Detail
  - put
```
ValueAndRmd<T> put(ValueAndRmd<T> oldValueAndRmd,
                   T newValue,
                   long putOperationTimestamp,
                   int putOperationColoID,
                   long newValueSourceOffset,
                   int newValueSourceBrokerID)
```
    Parameters:
    
    oldValueAndRmd - the old value and replication metadata which are persisted in the server prior to the write operation. Note that some implementation(s) may require the old value to be non-null. Please refer to the Javadoc of specific implementation.
    
    newValue - a record with all fields populated and with one of the registered value schemas
    
    putOperationTimestamp - the timestamp of the incoming write operation
    
    putOperationColoID - ID of the colo/fabric where this PUT request was originally received.
    
    newValueSourceOffset - The offset from which the new value originates in the realtime stream. Used to build the ReplicationMetadata for the newly inserted record.
    
    newValueSourceBrokerID - The ID of the broker from which the new value originates. ID's should correspond to the kafkaClusterUrlIdMap configured in the LeaderFollowerIngestionTask. Used to build the ReplicationMetadata for the newly inserted record.
    
    Returns:
    
    the resulting ValueAndRmd after merging the old one with the incoming write operation. The returned object is guaranteed to be "==" to the input oldValueAndReplicationMetadata object and the internal members of the object are possibly mutated.
  - delete
```
ValueAndRmd<T> delete(ValueAndRmd<T> oldValueAndRmd,
                      long deleteOperationTimestamp,
                      int deleteOperationColoID,
                      long newValueSourceOffset,
                      int newValueSourceBrokerID)
```
    Parameters:
    
    oldValueAndRmd - the old value and replication metadata which are persisted in the server prior to the write operation
    
    newValueSourceOffset - The offset from which the new value originates in the realtime stream. Used to build the ReplicationMetadata for the newly inserted record.
    
    deleteOperationColoID - ID of the colo/fabric where this DELETE request was originally received.
    
    newValueSourceBrokerID - The ID of the broker from which the new value originates. ID's should correspond to the kafkaClusterUrlIdMap configured in the LeaderFollowerIngestionTask. Used to build the ReplicationMetadata for the newly inserted record.
    
    Returns:
    
    the resulting ValueAndRmd after merging the old one with the incoming delete operation. The returned object is guaranteed to be "==" to the input oldValueAndReplicationMetadata object and the internal members of the object are possibly mutated.
  - update
```
ValueAndRmd<T> update(ValueAndRmd<T> oldValueAndRmd,
                      Lazy<org.apache.avro.generic.GenericRecord> writeOperation,
                      org.apache.avro.Schema currValueSchema,
                      long updateOperationTimestamp,
                      int updateOperationColoID,
                      long newValueSourceOffset,
                      int newValueSourceBrokerID)
```
    Parameters:
    
    oldValueAndRmd - the old value and replication metadata which are persisted in the server prior to the write operation
    
    writeOperation - a record with a write compute schema
    
    currValueSchema - Schema of the current value that is to-be-updated here.
    
    writeComputeSchema - Schema used to generate the write compute record. This schema could be a union and that is why this schema is needed when we already pass in the writeOperation generic record.
    
    updateOperationTimestamp - the timestamp of the incoming write operation
    
    updateOperationColoID - ID of the colo/fabric where this UPDATE request was originally received.
    
    newValueSourceOffset - The offset from which the new value originates in the realtime stream. Used to build the ReplicationMetadata for the newly inserted record.
    
    newValueSourceBrokerID - The ID of the broker from which the new value originates. ID's should correspond to the kafkaClusterUrlIdMap configured in the LeaderFollowerIngestionTask. Used to build the ReplicationMetadata for the newly inserted record.
    
    Returns:
    
    the resulting ValueAndRmd after merging the old one with the incoming write operation. The returned object is guaranteed to be "==" to the input oldValueAndReplicationMetadata object and the internal members of the object are possibly mutated.

Interface Merge<T>

Method Summary

Method Detail

put

delete

update