com.sleepycat.je.rep.arbitration.DesignatedPrimaryProvider Maven / Gradle / Ivy
/*-
* Copyright (C) 2002, 2018, Oracle and/or its affiliates. All rights reserved.
*
* This file was distributed by Oracle as part of a version of Oracle Berkeley
* DB Java Edition made available at:
*
* http://www.oracle.com/technetwork/database/database-technologies/berkeleydb/downloads/index.html
*
* Please see the LICENSE file included in the top-level directory of the
* appropriate version of Oracle Berkeley DB Java Edition for a copy of the
* license and additional information.
*/
package com.sleepycat.je.rep.arbitration;
import java.util.logging.Logger;
import com.sleepycat.je.Durability.ReplicaAckPolicy;
import com.sleepycat.je.rep.QuorumPolicy;
import com.sleepycat.je.rep.ReplicationMutableConfig;
import com.sleepycat.je.rep.impl.RepImpl;
import com.sleepycat.je.utilint.LoggerUtils;
/**
* Designated Primary arbitration relies on the configuration parameter
* je.rep.designatedPrimary. This form of arbitration is only effective when
* the electable group size is 2. When one of the two electable nodes goes
* down, the remaining node is permitted to win elections, retain authoritative
* mastership, and commit transactions without any participation from its dead
* sibling, if and only if it has been configured as designated primary.
*
* The user is responsible for ensuring that only one node at any time is
* annointed as the designated primary. There is some sanity checking that
* designated primary is only set by one node by master/replica syncups. The
* parameter is mutable.
*/
public class DesignatedPrimaryProvider implements ArbiterProvider {
private final RepImpl repImpl;
private final Logger logger;
DesignatedPrimaryProvider(RepImpl repImpl) {
this.repImpl = repImpl;
logger = LoggerUtils.getLogger(getClass());
}
/**
* Try to activate this node as a Primary, if it has been configured as
* such and if the group size is two. This method is invoked when an
* operation falls short of quorum requirements and is ready to trade
* durability for availability. More specifically it's invoked when an
* election fails, or there is an insufficient number of replicas during
* a begin transaction or a transaction commit.
*
* Active arbitration ends when the Non-Primary contacts it.
*
* @return true if the primary was activated.
*/
@Override
public boolean attemptActivation() {
if (checkDesignatedPrimary()) {
LoggerUtils.info(logger, repImpl,
"Primary activated; quorum is one.");
return true;
}
LoggerUtils.fine(logger, repImpl,
"Attempted unsuccessfully to activate designated " +
"primary");
return false;
}
/**
* Return true if this node is in a 2-node group and is configured as the
* Designated Primary, and is therefore capable of entering active
* arbitration.
*/
@Override
public boolean activationPossible() {
return checkDesignatedPrimary();
}
/**
* No cleannup is needed when exiting designated primary arbitration.
*/
@Override
public void endArbitration() {
/* nothing to do. */
}
/**
* Check the electable group size and the designated primary configuration
* to see if this node has the option of becoming the primary.
*/
private boolean checkDesignatedPrimary() {
return (repImpl != null) && /* repImpl can be null in unit tests */
repImpl.isDesignatedPrimary() &&
repImpl.getRepNode().getGroup().getElectableGroupSize() == 2;
}
/**
* When operating under designated primary arbitration, the election quorum
* is 1 for a group with electable group size of 2,
*/
@Override
public int getElectionQuorumSize(QuorumPolicy quorumPolicy) {
return 1;
}
/**
* Always returns 0, no replica acks are needed when acting under
* designated primary arbitration.
* TODO: is this still true with non voting nodes?
*/
@Override
public int getAckCount(ReplicaAckPolicy ackPolicy) {
return 0;
}
/**
* Return true if this node is no longer configured as the designated
* primary under the new configuration.
*/
@Override
public boolean shouldEndArbitration(ReplicationMutableConfig newConfig) {
return (!newConfig.getDesignatedPrimary());
}
}