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This component provides the means to set up a cluster of Neo4j instances that act together as a cluster, providing Master-Slave replication and other features.
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/*
 * Copyright (c) 2002-2016 "Neo Technology,"
 * Network Engine for Objects in Lund AB [http://neotechnology.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * 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 Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program. If not, see .
 */
package org.neo4j.kernel.ha;

import org.neo4j.graphdb.config.Setting;
import org.neo4j.graphdb.factory.Description;
import org.neo4j.helpers.HostnamePort;
import org.neo4j.kernel.configuration.ConfigurationMigrator;
import org.neo4j.kernel.configuration.Internal;
import org.neo4j.kernel.configuration.Migrator;
import org.neo4j.kernel.configuration.Settings;

import static org.neo4j.kernel.configuration.Settings.BOOLEAN;
import static org.neo4j.kernel.configuration.Settings.BYTES;
import static org.neo4j.kernel.configuration.Settings.DURATION;
import static org.neo4j.kernel.configuration.Settings.HOSTNAME_PORT;
import static org.neo4j.kernel.configuration.Settings.INTEGER;
import static org.neo4j.kernel.configuration.Settings.min;
import static org.neo4j.kernel.configuration.Settings.options;
import static org.neo4j.kernel.configuration.Settings.setting;
import static org.neo4j.kernel.ha.HaSettings.TxPushStrategy.fixed_ascending;

/**
 * Settings for High Availability mode
 */
@Description( "High Availability configuration settings" )
public class HaSettings
{
    @SuppressWarnings("unused") // accessed by reflection
    @Migrator
    public static final ConfigurationMigrator migrator = new EnterpriseConfigurationMigrator();

    @Description( "How long a slave will wait for response from master before giving up." )
    public static final Setting read_timeout = setting( "ha.slave_read_timeout", DURATION, "20s" );

    @Description( "Timeout for request threads waiting for instance to become master or slave." )
    public static final Setting state_switch_timeout = setting( "ha.role_switch_timeout", DURATION, "120s" );

    @Description( "Timeout for waiting for internal conditions during state switch, like for transactions "
            + "to complete, before switching to master or slave." )
    public static final Setting internal_state_switch_timeout =
            setting( "ha.internal_role_switch_timeout", DURATION, "10s" );

    @Description( "Timeout for taking remote (write) locks on slaves. Defaults to ha.slave_read_timeout." )
    public static final Setting lock_read_timeout = setting( "ha.slave_lock_timeout", DURATION, read_timeout );

    @Description( "Maximum number of connections a slave can have to the master." )
    public static final Setting max_concurrent_channels_per_slave =
            setting( "ha.max_channels_per_slave", INTEGER, "20", min( 1 ) );

    @Description( "Hostname and port to bind the HA server." )
    public static final Setting ha_server = setting( "ha.host.data", HOSTNAME_PORT, "0.0.0.0:6001-6011" );

    @Description("Whether this instance should only participate as slave in cluster. "
            + "If set to `true`, it will never be elected as master.")
    public static final Setting slave_only = setting( "ha.slave_only", BOOLEAN, Settings.FALSE );

    @Description( "Policy for how to handle branched data." )
    public static final Setting branched_data_policy = setting( "ha.branched_data_policy",
            options( BranchedDataPolicy.class ), "keep_all" );

    @Description( "Require authorization for access to the HA status endpoints." )
    public static final Setting ha_status_auth_enabled =
            setting( "dbms.security.ha_status_auth_enabled", BOOLEAN, Settings.TRUE );

    @Description( "Max size of the data chunks that flows between master and slaves in HA. Bigger size may increase " +
            "throughput, but may also be more sensitive to variations in bandwidth, whereas lower size increases " +
            "tolerance for bandwidth variations." )
    public static final Setting com_chunk_size = setting( "ha.data_chunk_size", BYTES, "2M", min( 1024L ) );

    @Description( "Interval of pulling updates from master." )
    public static final Setting pull_interval = setting( "ha.pull_interval", DURATION, "0s" );

    @Description( "The amount of slaves the master will ask to replicate a committed transaction. " )
    public static final Setting tx_push_factor = setting( "ha.tx_push_factor", INTEGER, "1", min( 0 ) );

    @Description( "Push strategy of a transaction to a slave during commit." )
    public static final Setting tx_push_strategy = setting( "ha.tx_push_strategy", options( TxPushStrategy.class ), fixed_ascending.name() );

    @Description( "Size of batches of transactions applied on slaves when pulling from master" )
    public static final Setting pull_apply_batch_size = setting( "ha.pull_batch_size", INTEGER, "100" );

    @Description( "Duration for which master will buffer ids and not reuse them to allow slaves read " +
                  "consistently. Slaves will also terminate transactions longer than this duration, when " +
                  "applying received transaction stream, to make sure they do not read potentially " +
                  "inconsistent/reused records." )
    @Internal
    public static final Setting id_reuse_safe_zone_time = setting( "unsupported.dbms.id_reuse_safe_zone", Settings.DURATION, "1h" );

    public enum TxPushStrategy
    {
        @Description("Round robin")
        round_robin,

        @Description("Fixed, prioritized by server id in descending order. This strategy will push to the same set of instances, as long as they remain " +
                     "available, and will prioritize available instances with the highest instance ids.")
        fixed_descending,

        @Description("Fixed, prioritized by server id in ascending order. This strategy will push to the same set of instances, as long as they remain " +
                     "available, and will prioritize those available instances with the lowest instance ids. This strategy makes it more likely that the most " +
                     "up-to-date instance in a cluster will be an instance with a low id. This is consistent with the master reelection tie-breaking strategy of letting the " +
                     "instance with the lowest id win an election if several instances are equally up-to-date. Thus, using this strategy makes it very likely " +
                     "that failover will happen in a low-id part of the cluster, which can be very helpful in planning a multi-data center deployment.")
        fixed_ascending
    }
}