org.apache.accumulo.server.fs.PreferredVolumeChooser.java Source code

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Here is the source code for org.apache.accumulo.server.fs.PreferredVolumeChooser.java

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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.accumulo.server.fs;

import static org.apache.commons.lang.ArrayUtils.EMPTY_STRING_ARRAY;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import java.util.function.Predicate;

import org.apache.accumulo.core.conf.Property;
import org.apache.accumulo.core.volume.Volume;
import org.apache.accumulo.server.client.HdfsZooInstance;
import org.apache.accumulo.server.conf.ServerConfigurationFactory;
import org.apache.accumulo.server.conf.TableConfiguration;
import org.apache.commons.collections.map.LRUMap;
import org.apache.commons.lang.StringUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * A {@link RandomVolumeChooser} that limits its choices from a given set of options to the subset of those options preferred for a particular table. Defaults
 * to selecting from all of the options presented. Can be customized via the table property {@value #PREFERRED_VOLUMES_CUSTOM_KEY}, which should contain a comma
 * separated list of {@link Volume} URIs. Note that both the property name and the format of its value are specific to this particular implementation.
 */
public class PreferredVolumeChooser extends RandomVolumeChooser implements VolumeChooser {
    private static final Logger log = LoggerFactory.getLogger(PreferredVolumeChooser.class);

    /**
     * This should match {@link Property#TABLE_ARBITRARY_PROP_PREFIX}
     */
    public static final String PREFERRED_VOLUMES_CUSTOM_KEY = "table.custom.preferredVolumes";
    // TODO ACCUMULO-3417 replace this with the ability to retrieve by String key.
    private static final Predicate<String> PREFERRED_VOLUMES_FILTER = key -> PREFERRED_VOLUMES_CUSTOM_KEY
            .equals(key);

    @SuppressWarnings("unchecked")
    private final Map<String, Set<String>> parsedPreferredVolumes = Collections.synchronizedMap(new LRUMap(1000));
    // TODO has to be lazily initialized currently because of the reliance on HdfsZooInstance. see ACCUMULO-3411
    private volatile ServerConfigurationFactory serverConfs;

    @Override
    public String choose(VolumeChooserEnvironment env, String[] options) {
        if (!env.hasTableId())
            return super.choose(env, options);

        // Get the current table's properties, and find the preferred volumes property
        // This local variable is an intentional component of the single-check idiom.
        ServerConfigurationFactory localConf = serverConfs;
        if (localConf == null) {
            // If we're under contention when first getting here we'll throw away some initializations.
            localConf = new ServerConfigurationFactory(HdfsZooInstance.getInstance());
            serverConfs = localConf;
        }
        TableConfiguration tableConf = localConf.getTableConfiguration(env.getTableId());
        final Map<String, String> props = new HashMap<String, String>();
        tableConf.getProperties(props, PREFERRED_VOLUMES_FILTER);
        if (props.isEmpty()) {
            log.warn("No preferred volumes specified. Defaulting to randomly choosing from instance volumes");
            return super.choose(env, options);
        }
        String volumes = props.get(PREFERRED_VOLUMES_CUSTOM_KEY);

        if (log.isTraceEnabled()) {
            log.trace("In custom chooser");
            log.trace("Volumes: " + volumes);
            log.trace("TableID: " + env.getTableId());
        }
        // If the preferred volumes property was specified, split the returned string by the comma and add use it to filter the given options.
        Set<String> preferred = parsedPreferredVolumes.get(volumes);
        if (preferred == null) {
            preferred = new HashSet<String>(Arrays.asList(StringUtils.split(volumes, ',')));
            parsedPreferredVolumes.put(volumes, preferred);
        }

        // Only keep the options that are in the preferred set
        final ArrayList<String> filteredOptions = new ArrayList<String>(Arrays.asList(options));
        filteredOptions.retainAll(preferred);

        // If there are no preferred volumes left, then warn the user and choose randomly from the instance volumes
        if (filteredOptions.isEmpty()) {
            log.warn(
                    "Preferred volumes are not instance volumes. Defaulting to randomly choosing from instance volumes");
            return super.choose(env, options);
        }

        // Randomly choose the volume from the preferred volumes
        String choice = super.choose(env, filteredOptions.toArray(EMPTY_STRING_ARRAY));
        if (log.isTraceEnabled()) {
            log.trace("Choice = " + choice);
        }
        return choice;
    }
}