public SegmentCacheManager(MondrianServer server) {
    this.server = server;
    ACTOR = new Actor();
    thread = new Thread(ACTOR, "mondrian.rolap.agg.SegmentCacheManager$ACTOR");
    thread.setDaemon(true);
    thread.start();

    // Create the index registry.
    this.indexRegistry = new SegmentCacheIndexRegistry();

    // Add a local cache, if needed.
    if (!MondrianProperties.instance().DisableCaching.get()) {
      final MemorySegmentCache cache = new MemorySegmentCache();
      segmentCacheWorkers.add(new SegmentCacheWorker(cache, thread));
    }

    // Add an external cache, if configured.
    final List<SegmentCache> externalCache = SegmentCacheWorker.initCache();
    for (SegmentCache cache : externalCache) {
      // Create a worker for this external cache
      segmentCacheWorkers.add(new SegmentCacheWorker(cache, thread));
      // Hook up a listener so it can update
      // the segment index.
      cache.addListener(new AsyncCacheListener(this, server));
    }

    compositeCache = new CompositeSegmentCache(segmentCacheWorkers);
  }
/**
 * Active object that maintains the "global cache" (in JVM, but shared between connections using a
 * particular schema) and "external cache" (as implemented by a {@link mondrian.spi.SegmentCache}.
 *
 * <p>Segment states
 *
 * <table>
 *     <tr><th>State</th><th>Meaning</th></tr>
 *     <tr><td>Local</td><td>Initial state of a segment</td></tr>
 * </table>
 *
 * <h2>Decisions to be reviewed</h2>
 *
 * <p>1. Create variant of actor that processes all requests synchronously, and does not need a
 * thread. This would be a more 'embedded' mode of operation (albeit with worse scale-out).
 *
 * <p>2. Move functionality into AggregationManager?
 *
 * <p>3. Delete {@link mondrian.rolap.RolapStar#lookupOrCreateAggregation} and {@link
 * mondrian.rolap.RolapStar#lookupSegment} and {@link
 * mondrian.rolap.RolapStar}.lookupAggregationShared (formerly RolapStar.lookupAggregation).
 *
 * <h2>Moved methods</h2>
 *
 * <p>(Keeping track of where methods came from will make it easier to merge to the mondrian-4 code
 * line.)
 *
 * <p>1. {@link mondrian.rolap.RolapStar#getCellFromCache} moved from {@link
 * Aggregation}.getCellValue
 *
 * <h2>Done</h2>
 *
 * <p>1. Obsolete CountingAggregationManager, and property
 * mondrian.rolap.agg.enableCacheHitCounters.
 *
 * <p>2. AggregationManager becomes non-singleton.
 *
 * <p>3. SegmentCacheWorker methods and segmentCache field become non-static. initCache() is called
 * on construction. SegmentCache is passed into constructor (therefore move ServiceDiscovery into
 * client). AggregationManager (or maybe MondrianServer) is another constructor parameter.
 *
 * <p>5. Move SegmentHeader, SegmentBody, ConstrainedColumn into mondrian.spi. Leave behind
 * dependencies on mondrian.rolap.agg. In particular, put code that converts Segment +
 * SegmentWithData to and from SegmentHeader + SegmentBody (e.g. {@link SegmentHeader}#forSegment)
 * into a utility class. (Do this as CLEANUP, after functionality is complete?)
 *
 * <p>6. Move functionality Aggregation to Segment. Long-term, Aggregation should not be used as a
 * 'gatekeeper' to Segment. Remove Aggregation fields columns and axes.
 *
 * <p>9. Obsolete {@link RolapStar#cacheAggregations}. Similar effect will be achieved by removing
 * the 'jvm cache' from the chain of caches.
 *
 * <p>10. Rename Aggregation.Axis to SegmentAxis.
 *
 * <p>11. Remove Segment.setData and instead split out subclass SegmentWithData. Now segment is
 * immutable. You don't have to wait for its state to change. You wait for a
 * Future&lt;SegmentWithData&gt; to become ready.
 *
 * <p>12. Remove methods: RolapCube.checkAggregateModifications,
 * RolapStar.checkAggregateModifications, RolapSchema.checkAggregateModifications,
 * RolapStar.pushAggregateModificationsToGlobalCache,
 * RolapSchema.pushAggregateModificationsToGlobalCache,
 * RolapCube.pushAggregateModificationsToGlobalCache.
 *
 * <p>13. Add new implementations of Future: CompletedFuture and SlotFuture.
 *
 * <p>14. Remove methods:
 *
 * <p>
 *
 * <ul>
 *   <li>Remove {@link SegmentLoader}.loadSegmentsFromCache - creates a {@link SegmentHeader} that
 *       has PRECISELY same specification as the requested segment, very unlikely to have a hit
 *   <li>Remove {@link SegmentLoader}.loadSegmentFromCacheRollup
 *   <li>Break up {@link SegmentLoader}.cacheSegmentData, and place code that is called after a
 *       segment has arrived
 * </ul>
 *
 * <p>13. Fix flush. Obsolete {@link Aggregation}.flush, and {@link RolapStar}.flush, which called
 * it.
 *
 * <p>18. {@code SegmentCacheManager#locateHeaderBody} (and maybe other methods) call {@link
 * SegmentCacheWorker#get}, and that's a slow blocking call. Make waits for segment futures should
 * be called from a worker or client, not an agent.
 *
 * <h2>Ideas and tasks</h2>
 *
 * <p>7. RolapStar.localAggregations and .sharedAggregations. Obsolete sharedAggregations.
 *
 * <p>8. Longer term. Move {@link mondrian.rolap.RolapStar.Bar}.segmentRefs to {@link
 * mondrian.server.Execution}. Would it still be thread-local?
 *
 * <p>10. Call {@link mondrian.spi.DataSourceChangeListener#isAggregationChanged}. Previously called
 * from {@link RolapStar}.checkAggregateModifications, now never called.
 *
 * <p>12. We can quickly identify segments affected by a flush using {@link
 * SegmentCacheIndex#intersectRegion}. But then what? Options:
 *
 * <ol>
 *   <li>Option #1. Pull them in, trim them, write them out? But: causes a lot of I/O, and we may
 *       never use these segments. Easiest.
 *   <li>Option #2. Mark the segments in the index as needing to be trimmed; trim them when read,
 *       and write out again. But: doesn't propagate to other nodes.
 *   <li>Option #3. (Best?) Write a mapping SegmentHeader->Restrictions into the cache. Less I/O
 *       than #1. Method "SegmentCache.addRestriction(SegmentHeader, CacheRegion)"
 * </ol>
 *
 * <p>14. Move {@link AggregationManager#getCellFromCache} somewhere else. It's concerned with local
 * segments, not the global/external cache.
 *
 * <p>15. Method to convert SegmentHeader + SegmentBody to Segment + SegmentWithData is imperfect.
 * Cannot parse predicates, compound predicates. Need mapping in star to do it properly and
 * efficiently? {@link mondrian.rolap.agg.SegmentBuilder.SegmentConverter} is a hack that can be
 * removed when this is fixed. See {@link SegmentBuilder#toSegment}. Also see #20.
 *
 * <p>17. Revisit the strategy for finding segments that can be copied from global and external
 * cache into local cache. The strategy of sending N {@link CellRequest}s at a time, then executing
 * SQL to fill in the gaps, is flawed. We need to maximize N in order to reduce segment
 * fragmentation, but if too high, we blow memory. BasicQueryTest.testAnalysis is an example of
 * this. Instead, we should send cell-requests in batches (is ~1000 the right size?), identify those
 * that can be answered from global or external cache, return those segments, but not execute SQL
 * until the end of the phase. If so, {@link CellRequestQuantumExceededException} be obsoleted.
 *
 * <p>19. Tracing. a. Remove or re-purpose {@link FastBatchingCellReader#pendingCount}; b. Add
 * counter to measure requests satisfied by calling {@link
 * mondrian.rolap.agg.SegmentCacheManager#peek}.
 *
 * <p>20. Obsolete {@link SegmentDataset} and its implementing classes. {@link SegmentWithData} can
 * use {@link SegmentBody} instead. Will save copying.
 *
 * <p>21. Obsolete {@link mondrian.util.CombiningGenerator}.
 *
 * <p>22. {@link SegmentHeader#constrain(mondrian.spi.SegmentColumn[])} is broken for N-dimensional
 * regions where N &gt; 1. Each call currently creates N more 1-dimensional regions, but should
 * create 1 more N-dimensional region. {@link SegmentHeader#excludedRegions} should be a list of
 * {@link SegmentColumn} arrays.
 *
 * <p>23. All code that calls {@link Future#get} should probably handle {@link
 * CancellationException}.
 *
 * <p>24. Obsolete {@link #handler}. Indirection doesn't win anything.
 *
 * @author jhyde
 */
public class SegmentCacheManager {
  private final Handler handler = new Handler();
  private final Actor ACTOR;
  public final Thread thread;

  /** Executor with which to send requests to external caches. */
  public final ExecutorService cacheExecutor =
      Util.getExecutorService(
          MondrianProperties.instance().SegmentCacheManagerNumberCacheThreads.get(),
          0,
          1,
          "mondrian.rolap.agg.SegmentCacheManager$cacheExecutor",
          new RejectedExecutionHandler() {
            public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
              throw MondrianResource.instance().SegmentCacheLimitReached.ex();
            }
          });

  /**
   * Executor with which to execute SQL requests.
   *
   * <p>TODO: create using factory and/or configuration parameters. Executor should be shared within
   * MondrianServer or target JDBC database.
   */
  public final ExecutorService sqlExecutor =
      Util.getExecutorService(
          MondrianProperties.instance().SegmentCacheManagerNumberSqlThreads.get(),
          0,
          1,
          "mondrian.rolap.agg.SegmentCacheManager$sqlExecutor",
          new RejectedExecutionHandler() {
            public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
              throw MondrianResource.instance().SqlQueryLimitReached.ex();
            }
          });

  // NOTE: This list is only mutable for testing purposes. Would rather it
  // were immutable.
  public final List<SegmentCacheWorker> segmentCacheWorkers =
      new CopyOnWriteArrayList<SegmentCacheWorker>();

  public final SegmentCache compositeCache;
  private final SegmentCacheIndexRegistry indexRegistry;

  private static final Logger LOGGER = Logger.getLogger(AggregationManager.class);
  private final MondrianServer server;

  public SegmentCacheManager(MondrianServer server) {
    this.server = server;
    ACTOR = new Actor();
    thread = new Thread(ACTOR, "mondrian.rolap.agg.SegmentCacheManager$ACTOR");
    thread.setDaemon(true);
    thread.start();

    // Create the index registry.
    this.indexRegistry = new SegmentCacheIndexRegistry();

    // Add a local cache, if needed.
    if (!MondrianProperties.instance().DisableCaching.get()) {
      final MemorySegmentCache cache = new MemorySegmentCache();
      segmentCacheWorkers.add(new SegmentCacheWorker(cache, thread));
    }

    // Add an external cache, if configured.
    final List<SegmentCache> externalCache = SegmentCacheWorker.initCache();
    for (SegmentCache cache : externalCache) {
      // Create a worker for this external cache
      segmentCacheWorkers.add(new SegmentCacheWorker(cache, thread));
      // Hook up a listener so it can update
      // the segment index.
      cache.addListener(new AsyncCacheListener(this, server));
    }

    compositeCache = new CompositeSegmentCache(segmentCacheWorkers);
  }

  public <T> T execute(Command<T> command) {
    return ACTOR.execute(handler, command);
  }

  public SegmentCacheIndexRegistry getIndexRegistry() {
    return indexRegistry;
  }

  /**
   * Adds a segment to segment index.
   *
   * <p>Called when a SQL statement has finished loading a segment.
   *
   * <p>Does not add the segment to the external cache. That is a potentially long-duration
   * operation, better carried out by a worker.
   *
   * @param header segment header
   * @param body segment body
   */
  public void loadSucceeded(RolapStar star, SegmentHeader header, SegmentBody body) {
    final Locus locus = Locus.peek();
    ACTOR.event(
        handler,
        new SegmentLoadSucceededEvent(
            System.currentTimeMillis(),
            locus.getServer().getMonitor(),
            locus.getServer().getId(),
            locus.execution.getMondrianStatement().getMondrianConnection().getId(),
            locus.execution.getMondrianStatement().getId(),
            locus.execution.getId(),
            star,
            header,
            body));
  }

  /**
   * Informs cache manager that a segment load failed.
   *
   * <p>Called when a SQL statement receives an error while loading a segment.
   *
   * @param header segment header
   * @param throwable Error
   */
  public void loadFailed(RolapStar star, SegmentHeader header, Throwable throwable) {
    final Locus locus = Locus.peek();
    ACTOR.event(
        handler,
        new SegmentLoadFailedEvent(
            System.currentTimeMillis(),
            locus.getServer().getMonitor(),
            locus.getServer().getId(),
            locus.execution.getMondrianStatement().getMondrianConnection().getId(),
            locus.execution.getMondrianStatement().getId(),
            locus.execution.getId(),
            star,
            header,
            throwable));
  }

  /**
   * Removes a segment from segment index.
   *
   * <p>Call is asynchronous. It comes back immediately.
   *
   * <p>Does not remove it from the external cache.
   *
   * @param header segment header
   */
  public void remove(RolapStar star, SegmentHeader header) {
    final Locus locus = Locus.peek();
    ACTOR.event(
        handler,
        new SegmentRemoveEvent(
            System.currentTimeMillis(),
            locus.getServer().getMonitor(),
            locus.getServer().getId(),
            locus.execution.getMondrianStatement().getMondrianConnection().getId(),
            locus.execution.getMondrianStatement().getId(),
            locus.execution.getId(),
            this,
            star,
            header));
  }

  /** Tells the cache that a segment is newly available in an external cache. */
  public void externalSegmentCreated(SegmentHeader header, MondrianServer server) {
    ACTOR.event(
        handler,
        new ExternalSegmentCreatedEvent(
            System.currentTimeMillis(),
            server.getMonitor(),
            server.getId(),
            0,
            0,
            0,
            this,
            header));
  }

  /** Tells the cache that a segment is no longer available in an external cache. */
  public void externalSegmentDeleted(SegmentHeader header, MondrianServer server) {
    ACTOR.event(
        handler,
        new ExternalSegmentDeletedEvent(
            System.currentTimeMillis(),
            server.getMonitor(),
            server.getId(),
            0,
            0,
            0,
            this,
            header));
  }

  public void printCacheState(CellRegion region, PrintWriter pw, Locus locus) {
    ACTOR.execute(handler, new PrintCacheStateCommand(region, pw, locus));
  }

  /** Shuts down this cache manager and all active threads and indexes. */
  public void shutdown() {
    execute(new ShutdownCommand());
    cacheExecutor.shutdown();
    sqlExecutor.shutdown();
  }

  public SegmentBuilder.SegmentConverter getConverter(RolapStar star, SegmentHeader header) {
    return indexRegistry
        .getIndex(star)
        .getConverter(
            header.schemaName,
            header.schemaChecksum,
            header.cubeName,
            header.rolapStarFactTableName,
            header.measureName,
            header.compoundPredicates);
  }

  /**
   * Makes a quick request to the aggregation manager to see whether the cell value required by a
   * particular cell request is in external cache.
   *
   * <p>'Quick' is relative. It is an asynchronous request (due to the aggregation manager being an
   * actor) and therefore somewhat slow. If the segment is in cache, will save batching up future
   * requests and re-executing the query. Win should be particularly noticeable for queries running
   * on a populated cache. Without this feature, every query would require at least two iterations.
   *
   * <p>Request does not issue SQL to populate the segment. Nor does it try to find existing
   * segments for rollup. Those operations can wait until next phase.
   *
   * <p>Client is responsible for adding the segment to its private cache.
   *
   * @param request Cell request
   * @return Segment with data, or null if not in cache
   */
  public SegmentWithData peek(final CellRequest request) {
    final SegmentCacheManager.PeekResponse response =
        execute(new PeekCommand(request, Locus.peek()));
    for (SegmentHeader header : response.headerMap.keySet()) {
      final SegmentBody body = compositeCache.get(header);
      if (body != null) {
        final SegmentBuilder.SegmentConverter converter =
            response.converterMap.get(SegmentCacheIndexImpl.makeConverterKey(header));
        if (converter != null) {
          return converter.convert(header, body);
        }
      }
    }
    for (Map.Entry<SegmentHeader, Future<SegmentBody>> entry : response.headerMap.entrySet()) {
      final Future<SegmentBody> bodyFuture = entry.getValue();
      if (bodyFuture != null) {
        final SegmentBody body = Util.safeGet(bodyFuture, "Waiting for segment to load");
        final SegmentHeader header = entry.getKey();
        final SegmentBuilder.SegmentConverter converter =
            response.converterMap.get(SegmentCacheIndexImpl.makeConverterKey(header));
        if (converter != null) {
          return converter.convert(header, body);
        }
      }
    }
    return null;
  }

  /** Visitor for messages (commands and events). */
  public interface Visitor {
    void visit(SegmentLoadSucceededEvent event);

    void visit(SegmentLoadFailedEvent event);

    void visit(SegmentRemoveEvent event);

    void visit(ExternalSegmentCreatedEvent event);

    void visit(ExternalSegmentDeletedEvent event);
  }

  private class Handler implements Visitor {
    public void visit(SegmentLoadSucceededEvent event) {
      indexRegistry.getIndex(event.star).loadSucceeded(event.header, event.body);

      event.monitor.sendEvent(
          new CellCacheSegmentCreateEvent(
              event.timestamp,
              event.serverId,
              event.connectionId,
              event.statementId,
              event.executionId,
              event.header.getConstrainedColumns().size(),
              event.body == null ? 0 : event.body.getValueMap().size(),
              CellCacheSegmentCreateEvent.Source.SQL));
    }

    public void visit(SegmentLoadFailedEvent event) {
      indexRegistry.getIndex(event.star).loadFailed(event.header, event.throwable);
    }

    public void visit(final SegmentRemoveEvent event) {
      indexRegistry.getIndex(event.star).remove(event.header);

      event.monitor.sendEvent(
          new CellCacheSegmentDeleteEvent(
              event.timestamp,
              event.serverId,
              event.connectionId,
              event.statementId,
              event.executionId,
              event.header.getConstrainedColumns().size(),
              CellCacheEvent.Source.CACHE_CONTROL));

      // Remove the segment from external caches. Use an executor, because
      // it may take some time. We discard the future, because we don't
      // care too much if it fails.
      final Future<?> future =
          event.cacheMgr.cacheExecutor.submit(
              new Runnable() {
                public void run() {
                  try {
                    // Note that the SegmentCache API doesn't require
                    // us to verify that the segment exists (by calling
                    // "contains") before we call "remove".
                    event.cacheMgr.compositeCache.remove(event.header);
                  } catch (Throwable e) {
                    LOGGER.warn("remove header failed: " + event.header, e);
                  }
                }
              });
      Util.safeGet(future, "SegmentCacheManager.segmentremoved");
    }

    public void visit(ExternalSegmentCreatedEvent event) {
      final SegmentCacheIndex index = event.cacheMgr.indexRegistry.getIndex(event.header);
      if (index != null) {
        index.add(event.header, false, null);
        event.monitor.sendEvent(
            new CellCacheSegmentCreateEvent(
                event.timestamp,
                event.serverId,
                event.connectionId,
                event.statementId,
                event.executionId,
                event.header.getConstrainedColumns().size(),
                0,
                CellCacheEvent.Source.EXTERNAL));
      }
    }

    public void visit(ExternalSegmentDeletedEvent event) {
      final SegmentCacheIndex index = event.cacheMgr.indexRegistry.getIndex(event.header);
      if (index != null) {
        index.remove(event.header);
        event.monitor.sendEvent(
            new CellCacheSegmentDeleteEvent(
                event.timestamp,
                event.serverId,
                event.connectionId,
                event.statementId,
                event.executionId,
                event.header.getConstrainedColumns().size(),
                CellCacheEvent.Source.EXTERNAL));
      }
    }
  }

  interface Message {}

  public static interface Command<T> extends Message, Callable<T> {
    Locus getLocus();
  }

  /** Command to flush a particular region from cache. */
  public static final class FlushCommand implements Command<FlushResult> {
    private final CellRegion region;
    private final CacheControlImpl cacheControlImpl;
    private final Locus locus;
    private final SegmentCacheManager cacheMgr;

    public FlushCommand(
        Locus locus,
        SegmentCacheManager mgr,
        CellRegion region,
        CacheControlImpl cacheControlImpl) {
      this.locus = locus;
      this.cacheMgr = mgr;
      this.region = region;
      this.cacheControlImpl = cacheControlImpl;
    }

    public Locus getLocus() {
      return locus;
    }

    public FlushResult call() throws Exception {
      // For each measure and each star, ask the index
      // which headers intersect.
      final List<SegmentHeader> headers = new ArrayList<SegmentHeader>();
      final List<Member> measures = CacheControlImpl.findMeasures(region);
      final SegmentColumn[] flushRegion = CacheControlImpl.findAxisValues(region);
      final List<RolapStar> starList = CacheControlImpl.getStarList(region);

      for (Member member : measures) {
        if (!(member instanceof RolapStoredMeasure)) {
          continue;
        }
        final RolapStoredMeasure storedMeasure = (RolapStoredMeasure) member;
        final RolapStar star = storedMeasure.getCube().getStar();
        final SegmentCacheIndex index = cacheMgr.indexRegistry.getIndex(star);
        headers.addAll(
            index.intersectRegion(
                member.getDimension().getSchema().getName(),
                ((RolapSchema) member.getDimension().getSchema()).getChecksum(),
                storedMeasure.getCube().getName(),
                storedMeasure.getName(),
                storedMeasure.getCube().getStar().getFactTable().getAlias(),
                flushRegion));
      }

      // If flushRegion is empty, this means we must clear all
      // segments for the region's measures.
      if (flushRegion.length == 0) {
        for (final SegmentHeader header : headers) {
          for (RolapStar star : starList) {
            cacheMgr.indexRegistry.getIndex(star).remove(header);
          }

          // Remove the segment from external caches. Use an
          // executor, because it may take some time. We discard
          // the future, because we don't care too much if it fails.
          cacheControlImpl.trace(
              "discard segment - it cannot be constrained and maintain consistency:\n"
                  + header.getDescription());

          final Future<?> task =
              cacheMgr.cacheExecutor.submit(
                  new Runnable() {
                    public void run() {
                      try {
                        // Note that the SegmentCache API doesn't
                        // require us to verify that the segment
                        // exists (by calling "contains") before we
                        // call "remove".
                        cacheMgr.compositeCache.remove(header);
                      } catch (Throwable e) {
                        LOGGER.warn("remove header failed: " + header, e);
                      }
                    }
                  });
          Util.safeGet(task, "SegmentCacheManager.flush");
        }
        return new FlushResult(Collections.<Callable<Boolean>>emptyList());
      }

      // Now we know which headers intersect. For each of them,
      // we append an excluded region.
      //
      // TODO: Optimize the logic here. If a segment is mostly
      // empty, we should trash it completely.
      final List<Callable<Boolean>> callableList = new ArrayList<Callable<Boolean>>();
      for (final SegmentHeader header : headers) {
        if (!header.canConstrain(flushRegion)) {
          // We have to delete that segment altogether.
          cacheControlImpl.trace(
              "discard segment - it cannot be constrained and maintain consistency:\n"
                  + header.getDescription());
          for (RolapStar star : starList) {
            cacheMgr.indexRegistry.getIndex(star).remove(header);
          }
          continue;
        }
        final SegmentHeader newHeader = header.constrain(flushRegion);
        for (final SegmentCacheWorker worker : cacheMgr.segmentCacheWorkers) {
          callableList.add(
              new Callable<Boolean>() {
                public Boolean call() throws Exception {
                  boolean existed;
                  if (worker.supportsRichIndex()) {
                    final SegmentBody sb = worker.get(header);
                    existed = worker.remove(header);
                    if (sb != null) {
                      worker.put(newHeader, sb);
                    }
                  } else {
                    // The cache doesn't support rich index. We
                    // have to clear the segment entirely.
                    existed = worker.remove(header);
                  }
                  return existed;
                }
              });
        }
        for (RolapStar star : starList) {
          SegmentCacheIndex index = cacheMgr.indexRegistry.getIndex(star);
          index.remove(header);
          index.add(newHeader, false, null);
        }
      }

      // Done
      return new FlushResult(callableList);
    }
  }

  private class PrintCacheStateCommand implements SegmentCacheManager.Command<Void> {
    private final PrintWriter pw;
    private final Locus locus;
    private final CellRegion region;

    public PrintCacheStateCommand(CellRegion region, PrintWriter pw, Locus locus) {
      this.region = region;
      this.pw = pw;
      this.locus = locus;
    }

    public Void call() {
      final List<RolapStar> starList = CacheControlImpl.getStarList(region);
      Collections.sort(
          starList,
          new Comparator<RolapStar>() {
            public int compare(RolapStar o1, RolapStar o2) {
              return o1.getFactTable().getAlias().compareTo(o2.getFactTable().getAlias());
            }
          });
      for (RolapStar star : starList) {
        indexRegistry.getIndex(star).printCacheState(pw);
      }
      return null;
    }

    public Locus getLocus() {
      return locus;
    }
  }

  /**
   * Result of a {@link FlushCommand}. Contains a list of tasks that must be executed by the caller
   * (or by an executor) to flush segments from the external cache(s).
   */
  public static class FlushResult {
    public final List<Callable<Boolean>> tasks;

    public FlushResult(List<Callable<Boolean>> tasks) {
      this.tasks = tasks;
    }
  }

  /** Special exception, thrown only by {@link ShutdownCommand}, telling the actor to shut down. */
  private static class PleaseShutdownException extends RuntimeException {
    private PleaseShutdownException() {}
  }

  private static class ShutdownCommand implements Command<String> {
    public ShutdownCommand() {}

    public String call() throws Exception {
      throw new PleaseShutdownException();
    }

    public Locus getLocus() {
      return null;
    }
  }

  private abstract static class Event implements Message {
    /**
     * Dispatches a call to the appropriate {@code visit} method on {@link
     * mondrian.server.monitor.Visitor}.
     *
     * @param visitor Visitor
     */
    public abstract void acceptWithoutResponse(Visitor visitor);
  }

  /**
   * Point for various clients in a request-response pattern to receive the response to their
   * requests.
   *
   * <p>The key type should test for object identity using the == operator, like {@link
   * java.util.WeakHashMap}. This allows responses to be automatically removed if the request (key)
   * is garbage collected.
   *
   * <p><b>Thread safety</b>. {@link #queue} is a thread-safe data structure; a thread can safely
   * call {@link #put} while another thread calls {@link #take}. The {@link #taken} map is not
   * thread safe, so you must lock the ResponseQueue before reading or writing it.
   *
   * <p>If requests are processed out of order, this queue is not ideal: until request #1 has
   * received its response, requests #2, #3 etc. will not receive their response. However, this is
   * not a problem for the monitor, which uses an actor model, processing requests in strict order.
   *
   * <p>REVIEW: This class is copy-pasted from {@link mondrian.server.monitor.Monitor}. Consider
   * abstracting common code.
   *
   * @param <K> request (key) type
   * @param <V> response (value) type
   */
  private static class ResponseQueue<K, V> {
    private final BlockingQueue<Pair<K, V>> queue;

    /**
     * Entries that have been removed from the queue. If the request is garbage-collected, the map
     * entry is removed.
     */
    private final Map<K, V> taken = new WeakHashMap<K, V>();

    /**
     * Creates a ResponseQueue with given capacity.
     *
     * @param capacity Capacity
     */
    public ResponseQueue(int capacity) {
      queue = new ArrayBlockingQueue<Pair<K, V>>(capacity);
    }

    /**
     * Places a (request, response) pair onto the queue.
     *
     * @param k Request
     * @param v Response
     * @throws InterruptedException if interrupted while waiting
     */
    public void put(K k, V v) throws InterruptedException {
      queue.put(Pair.of(k, v));
    }

    /**
     * Retrieves the response from the queue matching the given key, blocking until it is received.
     *
     * @param k Response
     * @return Response
     * @throws InterruptedException if interrupted while waiting
     */
    public synchronized V take(K k) throws InterruptedException {
      final V v = taken.remove(k);
      if (v != null) {
        return v;
      }
      // Take the laundry out of the machine. If it's ours, leave with it.
      // If it's someone else's, fold it neatly and put it on the pile.
      for (; ; ) {
        final Pair<K, V> pair = queue.take();
        if (pair.left.equals(k)) {
          return pair.right;
        } else {
          taken.put(pair.left, pair.right);
        }
      }
    }
  }

  /** Copy-pasted from {@link mondrian.server.monitor.Monitor}. Consider abstracting common code. */
  private static class Actor implements Runnable {

    private final BlockingQueue<Pair<Handler, Message>> eventQueue =
        new ArrayBlockingQueue<Pair<Handler, Message>>(1000);

    private final ResponseQueue<Command<?>, Pair<Object, Throwable>> responseQueue =
        new ResponseQueue<Command<?>, Pair<Object, Throwable>>(1000);

    public void run() {
      try {
        for (; ; ) {
          final Pair<Handler, Message> entry = eventQueue.take();
          final Handler handler = entry.left;
          final Message message = entry.right;
          try {
            // A message is either a command or an event.
            // A command returns a value that must be read by
            // the caller.
            if (message instanceof Command<?>) {
              Command<?> command = (Command<?>) message;
              try {
                Locus.push(command.getLocus());
                Object result = command.call();
                responseQueue.put(command, Pair.of(result, (Throwable) null));
              } catch (PleaseShutdownException e) {
                responseQueue.put(command, Pair.of(null, (Throwable) null));
                return; // exit event loop
              } catch (Throwable e) {
                responseQueue.put(command, Pair.of(null, e));
              } finally {
                Locus.pop(command.getLocus());
              }
            } else {
              Event event = (Event) message;
              event.acceptWithoutResponse(handler);

              // Broadcast the event to anyone who is interested.
              RolapUtil.MONITOR_LOGGER.debug(message);
            }
          } catch (Throwable e) {
            // REVIEW: Somewhere better to send it?
            e.printStackTrace();
          }
        }
      } catch (InterruptedException e) {
        // REVIEW: Somewhere better to send it?
        e.printStackTrace();
      } catch (Throwable e) {
        e.printStackTrace();
      }
    }

    <T> T execute(Handler handler, Command<T> command) {
      try {
        eventQueue.put(Pair.<Handler, Message>of(handler, command));
      } catch (InterruptedException e) {
        throw Util.newError(e, "Exception while executing " + command);
      }
      try {
        final Pair<Object, Throwable> pair = responseQueue.take(command);
        if (pair.right != null) {
          if (pair.right instanceof RuntimeException) {
            throw (RuntimeException) pair.right;
          } else if (pair.right instanceof Error) {
            throw (Error) pair.right;
          } else {
            throw new RuntimeException(pair.right);
          }
        } else {
          return (T) pair.left;
        }
      } catch (InterruptedException e) {
        throw Util.newError(e, "Exception while executing " + command);
      }
    }

    public void event(Handler handler, Event event) {
      try {
        eventQueue.put(Pair.<Handler, Message>of(handler, event));
      } catch (InterruptedException e) {
        throw Util.newError(e, "Exception while executing " + event);
      }
    }
  }

  private static class SegmentLoadSucceededEvent extends Event {
    private final SegmentHeader header;
    private final SegmentBody body;
    private final long timestamp;
    private final RolapStar star;
    private final int serverId;
    private final int connectionId;
    private final long statementId;
    private final long executionId;
    private final Monitor monitor;

    public SegmentLoadSucceededEvent(
        long timestamp,
        Monitor monitor,
        int serverId,
        int connectionId,
        long statementId,
        long executionId,
        RolapStar star,
        SegmentHeader header,
        SegmentBody body) {
      this.timestamp = timestamp;
      this.monitor = monitor;
      this.serverId = serverId;
      this.connectionId = connectionId;
      this.statementId = statementId;
      this.executionId = executionId;
      assert header != null;
      assert star != null;
      this.star = star;
      this.header = header;
      this.body = body; // may be null
    }

    public void acceptWithoutResponse(Visitor visitor) {
      visitor.visit(this);
    }
  }

  private static class SegmentLoadFailedEvent extends Event {
    private final SegmentHeader header;
    private final Throwable throwable;
    private final long timestamp;
    private final RolapStar star;
    private final Monitor monitor;
    private final int serverId;
    private final int connectionId;
    private final long statementId;
    private final long executionId;

    public SegmentLoadFailedEvent(
        long timestamp,
        Monitor monitor,
        int serverId,
        int connectionId,
        long statementId,
        long executionId,
        RolapStar star,
        SegmentHeader header,
        Throwable throwable) {
      this.timestamp = timestamp;
      this.monitor = monitor;
      this.serverId = serverId;
      this.connectionId = connectionId;
      this.statementId = statementId;
      this.executionId = executionId;
      this.star = star;
      this.throwable = throwable;
      assert header != null;
      this.header = header;
    }

    public void acceptWithoutResponse(Visitor visitor) {
      visitor.visit(this);
    }
  }

  private static class SegmentRemoveEvent extends Event {
    private final SegmentHeader header;
    private final long timestamp;
    private final Monitor monitor;
    private final int serverId;
    private final int connectionId;
    private final long statementId;
    private final long executionId;
    private final RolapStar star;
    private final SegmentCacheManager cacheMgr;

    public SegmentRemoveEvent(
        long timestamp,
        Monitor monitor,
        int serverId,
        int connectionId,
        long statementId,
        long executionId,
        SegmentCacheManager cacheMgr,
        RolapStar star,
        SegmentHeader header) {
      this.timestamp = timestamp;
      this.monitor = monitor;
      this.serverId = serverId;
      this.connectionId = connectionId;
      this.statementId = statementId;
      this.executionId = executionId;
      this.cacheMgr = cacheMgr;
      this.star = star;
      assert header != null;
      this.header = header;
    }

    public void acceptWithoutResponse(Visitor visitor) {
      visitor.visit(this);
    }
  }

  private static class ExternalSegmentCreatedEvent extends Event {
    private final SegmentCacheManager cacheMgr;
    private final SegmentHeader header;
    private final long timestamp;
    private final Monitor monitor;
    private final int serverId;
    private final int connectionId;
    private final long statementId;
    private final long executionId;

    public ExternalSegmentCreatedEvent(
        long timestamp,
        Monitor monitor,
        int serverId,
        int connectionId,
        long statementId,
        long executionId,
        SegmentCacheManager cacheMgr,
        SegmentHeader header) {
      this.timestamp = timestamp;
      this.monitor = monitor;
      this.serverId = serverId;
      this.connectionId = connectionId;
      this.statementId = statementId;
      this.executionId = executionId;
      assert header != null;
      assert cacheMgr != null;
      this.cacheMgr = cacheMgr;
      this.header = header;
    }

    public void acceptWithoutResponse(Visitor visitor) {
      visitor.visit(this);
    }
  }

  private static class ExternalSegmentDeletedEvent extends Event {
    private final SegmentCacheManager cacheMgr;
    private final SegmentHeader header;
    private final long timestamp;
    private final Monitor monitor;
    private final int serverId;
    private final int connectionId;
    private final long statementId;
    private final long executionId;

    public ExternalSegmentDeletedEvent(
        long timestamp,
        Monitor monitor,
        int serverId,
        int connectionId,
        long statementId,
        long executionId,
        SegmentCacheManager cacheMgr,
        SegmentHeader header) {
      this.timestamp = timestamp;
      this.monitor = monitor;
      this.serverId = serverId;
      this.connectionId = connectionId;
      this.statementId = statementId;
      this.executionId = executionId;
      assert header != null;
      assert cacheMgr != null;
      this.cacheMgr = cacheMgr;
      this.header = header;
    }

    public void acceptWithoutResponse(Visitor visitor) {
      visitor.visit(this);
    }
  }

  /**
   * Implementation of SegmentCacheListener that updates the segment index of its aggregation
   * manager instance when it receives events from its assigned SegmentCache implementation.
   */
  private static class AsyncCacheListener implements SegmentCache.SegmentCacheListener {
    private final SegmentCacheManager cacheMgr;
    private final MondrianServer server;

    public AsyncCacheListener(SegmentCacheManager cacheMgr, MondrianServer server) {
      this.cacheMgr = cacheMgr;
      this.server = server;
    }

    public void handle(final SegmentCacheEvent e) {
      if (e.isLocal()) {
        return;
      }
      Locus.execute(
          Execution.NONE,
          "AsyncCacheListener.handle",
          new Locus.Action<Void>() {
            public Void execute() {
              final SegmentCacheManager.Command<Void> command;
              final Locus locus = Locus.peek();
              switch (e.getEventType()) {
                case ENTRY_CREATED:
                  command =
                      new Command<Void>() {
                        public Void call() {
                          cacheMgr.externalSegmentCreated(e.getSource(), server);
                          return null;
                        }

                        public Locus getLocus() {
                          return locus;
                        }
                      };
                  break;
                case ENTRY_DELETED:
                  command =
                      new Command<Void>() {
                        public Void call() {
                          cacheMgr.externalSegmentDeleted(e.getSource(), server);
                          return null;
                        }

                        public Locus getLocus() {
                          return locus;
                        }
                      };
                  break;
                default:
                  throw new UnsupportedOperationException();
              }
              cacheMgr.execute(command);
              return null;
            }
          });
    }
  }

  /**
   * Makes a collection of {@link SegmentCacheWorker} objects (each of which is backed by a {@link
   * SegmentCache} appear to be a SegmentCache.
   *
   * <p>For most operations, it is easier to operate on a single cache. It is usually clear whether
   * operations should quit when finding the first match, or to operate on all workers. (For
   * example, {@link #remove} tries to remove the segment header from all workers, and returns
   * whether it was removed from any of them.) This class just does what seems most typical. If you
   * want another behavior for a particular operation, operate on the workers directly.
   */
  private static class CompositeSegmentCache implements SegmentCache {
    private final List<SegmentCacheWorker> workers;

    public CompositeSegmentCache(List<SegmentCacheWorker> workers) {
      this.workers = workers;
    }

    public SegmentBody get(SegmentHeader header) {
      for (SegmentCacheWorker worker : workers) {
        final SegmentBody body = worker.get(header);
        if (body != null) {
          return body;
        }
      }
      return null;
    }

    public boolean contains(SegmentHeader header) {
      for (SegmentCacheWorker worker : workers) {
        if (worker.contains(header)) {
          return true;
        }
      }
      return false;
    }

    public List<SegmentHeader> getSegmentHeaders() {
      // Special case 0 and 1 workers, for which the 'union' operation
      // is trivial.
      switch (workers.size()) {
        case 0:
          return Collections.emptyList();
        case 1:
          return workers.get(0).getSegmentHeaders();
        default:
          final List<SegmentHeader> list = new ArrayList<SegmentHeader>();
          final Set<SegmentHeader> set = new HashSet<SegmentHeader>();
          for (SegmentCacheWorker worker : workers) {
            for (SegmentHeader header : worker.getSegmentHeaders()) {
              if (set.add(header)) {
                list.add(header);
              }
            }
          }
          return list;
      }
    }

    public boolean put(SegmentHeader header, SegmentBody body) {
      for (SegmentCacheWorker worker : workers) {
        worker.put(header, body);
      }
      return true;
    }

    public boolean remove(SegmentHeader header) {
      boolean result = false;
      for (SegmentCacheWorker worker : workers) {
        if (worker.remove(header)) {
          result = true;
        }
      }
      return result;
    }

    public void tearDown() {
      // nothing
    }

    public void addListener(SegmentCacheListener listener) {
      // nothing
    }

    public void removeListener(SegmentCacheListener listener) {
      // nothing
    }

    public boolean supportsRichIndex() {
      return false;
    }
  }

  /**
   * Locates segments in the cache that satisfy a given request.
   *
   * <p>The result consists of (a) a list of segment headers, (b) a list of futures for segment
   * bodies that are currently being loaded, (c) converters to convert headers into {@link
   * SegmentWithData}.
   *
   * <p>For (a), the client should call the cache to get the body for each segment header; it is
   * possible that there is no body in the cache. For (b), the client will have to wait for the
   * segment to arrive.
   */
  private class PeekCommand implements SegmentCacheManager.Command<PeekResponse> {
    private final CellRequest request;
    private final Locus locus;

    /**
     * Creates a PeekCommand.
     *
     * @param request Cell request
     * @param locus Locus
     */
    public PeekCommand(CellRequest request, Locus locus) {
      this.request = request;
      this.locus = locus;
    }

    public PeekResponse call() {
      final RolapStar.Measure measure = request.getMeasure();
      final RolapStar star = measure.getStar();
      final RolapSchema schema = star.getSchema();
      final AggregationKey key = new AggregationKey(request);
      final List<SegmentHeader> headers =
          indexRegistry
              .getIndex(star)
              .locate(
                  schema.getName(),
                  schema.getChecksum(),
                  measure.getCubeName(),
                  measure.getName(),
                  star.getFactTable().getAlias(),
                  request.getConstrainedColumnsBitKey(),
                  request.getMappedCellValues(),
                  AggregationKey.getCompoundPredicateStringList(
                      star, key.getCompoundPredicateList()));

      final Map<SegmentHeader, Future<SegmentBody>> headerMap =
          new HashMap<SegmentHeader, Future<SegmentBody>>();
      final Map<List, SegmentBuilder.SegmentConverter> converterMap =
          new HashMap<List, SegmentBuilder.SegmentConverter>();

      // Is there a pending segment? (A segment that has been created and
      // is loading via SQL.)
      for (final SegmentHeader header : headers) {
        final Future<SegmentBody> bodyFuture = indexRegistry.getIndex(star).getFuture(header);
        if (bodyFuture != null) {
          // Check if the DataSourceChangeListener wants us to clear
          // the current segment
          if (star.getChangeListener() != null
              && star.getChangeListener().isAggregationChanged(key)) {
            /*
             * We can't satisfy this request, and we must clear the
             * data from our cache. We clear it from the index
             * first, then queue up a job in the background
             * to remove the data from all the caches.
             */
            indexRegistry.getIndex(star).remove(header);
            Util.safeGet(
                cacheExecutor.submit(
                    new Runnable() {
                      public void run() {
                        try {
                          compositeCache.remove(header);
                        } catch (Throwable e) {
                          LOGGER.warn("remove header failed: " + header, e);
                        }
                      }
                    }),
                "SegmentCacheManager.peek");
          }
          converterMap.put(
              SegmentCacheIndexImpl.makeConverterKey(header), getConverter(star, header));
          headerMap.put(header, bodyFuture);
        }
      }

      return new PeekResponse(headerMap, converterMap);
    }

    public Locus getLocus() {
      return locus;
    }
  }

  private static class PeekResponse {
    public final Map<SegmentHeader, Future<SegmentBody>> headerMap;
    public final Map<List, SegmentBuilder.SegmentConverter> converterMap;

    public PeekResponse(
        Map<SegmentHeader, Future<SegmentBody>> headerMap,
        Map<List, SegmentBuilder.SegmentConverter> converterMap) {
      this.headerMap = headerMap;
      this.converterMap = converterMap;
    }
  }

  /**
   * Registry of all the indexes that were created for this cache manager, per {@link RolapStar}.
   */
  public class SegmentCacheIndexRegistry {
    private final Map<RolapStar, SegmentCacheIndex> indexes =
        new ReferenceMap(ReferenceMap.WEAK, ReferenceMap.SOFT);
    /** Returns the {@link SegmentCacheIndex} for a given {@link RolapStar}. */
    public SegmentCacheIndex getIndex(RolapStar star) {
      if (!indexes.containsKey(star)) {
        indexes.put(star, new SegmentCacheIndexImpl(thread));
      }
      return indexes.get(star);
    }
    /** Returns the {@link SegmentCacheIndex} for a given {@link SegmentHeader}. */
    private SegmentCacheIndex getIndex(SegmentHeader header) {
      // First we check the indexes that already exist.
      // This is fast.
      for (Entry<RolapStar, SegmentCacheIndex> entry : indexes.entrySet()) {
        final String factTableName = entry.getKey().getFactTable().getTableName();
        final ByteString schemaChecksum = entry.getKey().getSchema().getChecksum();
        if (!factTableName.equals(header.rolapStarFactTableName)) {
          continue;
        }
        if (!schemaChecksum.equals(header.schemaChecksum)) {
          continue;
        }
        return entry.getValue();
      }
      // The index doesn't exist. Let's create it.
      for (RolapSchema schema : RolapSchema.getRolapSchemas()) {
        if (!schema.getChecksum().equals(header.schemaChecksum)) {
          continue;
        }
        // We have a schema match.
        RolapStar star = schema.getStar(header.rolapStarFactTableName);
        if (star != null) {
          // Found it.
          indexes.put(star, new SegmentCacheIndexImpl(thread));
        }
        return indexes.get(star);
      }
      return null;
    }
  }
}