core/src/main/java/org/apache/accumulo/core/spi/balancer/RegexGroupBalancer.java

/*
 * 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.core.spi.balancer;

import java.util.function.Function;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import org.apache.accumulo.core.conf.ConfigurationTypeHelper;
import org.apache.accumulo.core.conf.Property;
import org.apache.accumulo.core.data.TableId;
import org.apache.accumulo.core.data.TabletId;
import org.apache.accumulo.core.spi.common.ServiceEnvironment;
import org.apache.hadoop.io.Text;

/**
 * A {@link GroupBalancer} that groups tablets using a configurable regex. To use this balancer
 * configure the following settings for your table then configure this balancer for your table.
 *
 * <ul>
 * <li>Set {@code table.custom.balancer.group.regex.pattern} to a regular expression. This regular
 * expression must have one group. The regex is applied to the tablet end row and whatever the regex
 * group matches is used as the group. For example with a regex of {@code (\d\d).*} and an end row
 * of {@code 12abc}, the group for the tablet would be {@code 12}.
 * <li>Set {@code table.custom.balancer.group.regex.default} to a default group. This group is
 * returned for the last tablet in the table and tablets for which the regex does not match.
 * <li>Optionally set {@code table.custom.balancer.group.regex.wait.time} to time (can use time
 * suffixes). This determines how long to wait between balancing. Since this balancer scans the
 * metadata table, may want to set this higher for large tables.
 * </ul>
 *
 * @since 2.1.0
 */
public class RegexGroupBalancer extends GroupBalancer {

  public static final String REGEX_PROPERTY =
      Property.TABLE_ARBITRARY_PROP_PREFIX.getKey() + "balancer.group.regex.pattern";
  public static final String DEFAUT_GROUP_PROPERTY =
      Property.TABLE_ARBITRARY_PROP_PREFIX.getKey() + "balancer.group.regex.default";
  public static final String WAIT_TIME_PROPERTY =
      Property.TABLE_ARBITRARY_PROP_PREFIX.getKey() + "balancer.group.regex.wait.time";

  private final TableId tableId;

  public RegexGroupBalancer(TableId tableId) {
    super(tableId);
    this.tableId = tableId;
  }

  @Override
  protected long getWaitTime() {
    ServiceEnvironment.Configuration conf = environment.getConfiguration(tableId);
    if (conf.isSet(WAIT_TIME_PROPERTY)) {
      return ConfigurationTypeHelper.getTimeInMillis(conf.get(WAIT_TIME_PROPERTY));
    }
    return super.getWaitTime();
  }

  @Override
  protected Function<TabletId,String> getPartitioner() {

    ServiceEnvironment.Configuration conf = environment.getConfiguration(tableId);
    String regex = conf.get(REGEX_PROPERTY);
    final String defaultGroup = conf.get(DEFAUT_GROUP_PROPERTY);

    final Pattern pattern = Pattern.compile(regex);

    return input -> {
      Text er = input.getEndRow();
      if (er == null) {
        return defaultGroup;
      }

      Matcher matcher = pattern.matcher(er.toString());
      if (matcher.matches() && matcher.groupCount() == 1) {
        return matcher.group(1);
      }

      return defaultGroup;
    };
  }
}