net.openhft.chronicle.map.Replica Maven / Gradle / Ivy
/*
* Copyright (C) 2015 higherfrequencytrading.com
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation, either version 3 of the License.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this program. If not, see An identifier is used
* to determine which replicating node made the change.
If two nodes update their map at the
* same time with different values, we have to deterministically resolve which update wins,
* because of eventual consistency both nodes should end up locally holding the same data.
* Although it is rare two remote nodes could receive an update to their maps at exactly the
* same time for the same key, we have to handle this edge case, its therefore important not to
* rely on timestamps alone to reconcile the updates. Typically the update with the newest
* timestamp should win, but in this example both timestamps are the same, and the decision
* made to one node should be identical to the decision made to the other. We resolve this
* simple dilemma by using a node identifier, each node will have a unique identifier, the
* update from the node with the smallest identifier wins.
*
* @return the unique Identifier associated with this map instance
*/
byte identifier();
/**
* Gets (if it does not exist, creates) an instance of ModificationIterator associated with a
* remote node, this weak associated is bound using the {@code identifier}.
*
* @param remoteIdentifier the identifier of the remote node
* @return the ModificationIterator dedicated for replication to the remote node with the given
* identifier
* @see #identifier()
*/
ModificationIterator acquireModificationIterator(byte remoteIdentifier);
/**
* Returns the timestamp of the last change from the specified remote node, already replicated
* to this Replica.
Used in conjunction with replication, to back fill data from a remote
* node. This node may have missed updates while it was not been running or connected via TCP.
*
* @param remoteIdentifier the identifier of the remote node to check last replicated update
* time from
* @return a timestamp of the last modification to an entry, or 0 if there are no entries.
* @see #identifier()
*/
long lastModificationTime(byte remoteIdentifier);
void setLastModificationTime(byte identifier, long timestamp);
/**
* notifies when there is a changed to the modification iterator
*/
interface ModificationNotifier {
ModificationNotifier NOP = new ModificationNotifier() {
@Override
public void onChange() {
}
};
/**
* called when ever there is a change applied to the modification iterator
*/
void onChange();
}
/**
* Holds a record of which entries have modification. Each remote map supported will require a
* corresponding ModificationIterator instance
*/
interface ModificationIterator {
/**
* @return {@code true} if the is another entry to be received via {@link
* #nextEntry(Replica.EntryCallback, int chronicleId)}
*/
boolean hasNext();
/**
* A non-blocking call that provides the entry that has changed to {@code
* callback.onEntry()}.
*
* @param callback a callback which will be called when a new entry becomes available.
* @param chronicleId only assigned when using chronicle channels
* @return {@code true} if the entry was accepted by the {@code callback.onEntry()} method,
* {@code false} if the entry was not accepted or was not available
*/
boolean nextEntry(@NotNull final EntryCallback callback, final int chronicleId) throws InterruptedException;
/**
* Dirties all entries with a modification time equal to {@code fromTimeStamp} or newer. It
* means all these entries will be considered as "new" by this ModificationIterator and
* iterated once again no matter if they have already been.
This functionality is used
* to publish recently modified entries to a new remote node as it connects.
*
* @param fromTimeStamp the timestamp from which all entries should be dirty
*/
void dirtyEntries(long fromTimeStamp);
/**
* the {@code modificationNotifier} is called when ever there is a change applied to the
* modification iterator
*
* @param modificationNotifier gets notified when a change occurs
*/
void setModificationNotifier(@NotNull final ModificationNotifier modificationNotifier);
}
/**
* supports reading and writing serialize entries
*/
interface EntryExternalizable {
/**
* The size of entry in bytes
*
* @param entry an entry in the map
* @param chronicleId is the channel id used to identify the canonical map or queue
* @return the size of the entry
*/
int sizeOfEntry(@NotNull Bytes entry, int chronicleId);
/**
* check that the identifier in the entry is from this node
*
* @param entry an entry in the map
* @param chronicleId is the channel id used to identify the canonical map or queue
* @return the size of the entry
*/
boolean identifierCheck(@NotNull Bytes entry, int chronicleId);
/**
* The map implements this method to save its contents.
* @param entry the byte location of the entry to be stored
* @param destination a buffer the entry will be written to, the segment may reject this
* operation and add zeroBytes, if the identifier in the entry did not
* match the maps local
* @param chronicleId is the channel id used to identify the canonical map or queue
* @param bootstrapTime
*/
void writeExternalEntry(@NotNull Bytes entry,
@NotNull Bytes destination,
int chronicleId,
long bootstrapTime);
/**
* The map implements this method to restore its contents. This method must read the values
* in the same sequence and with the same types as were written by {@code
* writeExternalEntry()}. This method is typically called when we receive a remote
* replication event, this event could originate from either a remote {@code put(K key, V
*value)} or {@code remove(Object key)}
*
* @param copies
* @param segmentState
* @param source bytes to read an entry from
*/
void readExternalEntry(@NotNull ThreadLocalCopies copies,
@NotNull VanillaChronicleMap.SegmentState segmentState,
@NotNull Bytes source);
}
/**
* provides a key and value from NativeBytes, this can be used in conjunction with the
* modification iterator to get the key and value out of the NativeBytes
*/
interface EntryResolver {
/**
* gets the key from the entry
*
* @param entry the bytes which the bytes which point to the entry
* @param usingKey the key object to reuse, if possible
* @return the key which is in the entry
*/
K key(@NotNull Bytes entry, K usingKey);
/**
* gets the value from the entry
*
* @param entry the bytes which reference to the entry
* @param usingValue the value object to reuse, if possible
* @return the value which is in the entry or null if the value has been remove from the map
*/
V value(@NotNull Bytes entry, V usingValue);
boolean wasRemoved(@NotNull Bytes entry);
}
/**
* Implemented typically by a replicator, This interface provides the event, which will get
* called whenever a put() or remove() has occurred to the map
*/
abstract class EntryCallback {
/**
* Called whenever a put() or remove() has occurred to a replicating map.
*
* @param entry the entry you will receive, this does not have to be locked, as
* locking is already provided from the caller.
* @param chronicleId only assigned when clustering
* @param bootStrapTimeStamp sent to the client on every update this is the timestamp
* that the remote client should bootstrap from when there has
* been a disconnection, this time maybe later than the message
* time as event are not send in chronological order from the
* bit set.
*
*
* @return {@code false} if this entry should be ignored because the identifier of the
* source node is not from one of our changes, WARNING even though we check the identifier
* in the ModificationIterator the entry may have been updated.
*/
public abstract boolean onEntry(@NotNull Bytes entry,
int chronicleId,
long bootStrapTimeStamp);
/**
* Called just after {@link #onEntry(Bytes, int, long)}. No-op by default.
*/
public void onAfterEntry() {
}
/**
* Called just before {@link #onEntry(Bytes, int, long)}. No-op by default.
*/
public void onBeforeEntry() {
}
/**
* its possible that the entry should now be ignored, for example although rare its
* identifier may have recently been changed by another thread, so its no longer applicable
* to send
*
* @param entry the entry you will receive, this does not have to be locked, as
* locking is already provided from the caller.
* @param chronicleId only assigned when clustering
* @return {@code true} if this entry should be ignored
*/
public abstract boolean shouldBeIgnored(final Bytes entry, final int chronicleId);
}
}