src/org/objectweb/cjdbc/controller/loadbalancer/raidb2/RAIDb2_RR.java

説明を見る。

package org.objectweb.cjdbc.controller.loadbalancer.raidb2;

import java.sql.SQLException;
import java.util.ArrayList;

import org.objectweb.cjdbc.common.exceptions.NoMoreBackendException;
import org.objectweb.cjdbc.common.exceptions.UnreachableBackendException;
import org.objectweb.cjdbc.common.i18n.Translate;
import org.objectweb.cjdbc.common.sql.SelectRequest;
import org.objectweb.cjdbc.common.sql.StoredProcedure;
import org.objectweb.cjdbc.common.xml.DatabasesXmlTags;
import org.objectweb.cjdbc.controller.backend.DatabaseBackend;
import org.objectweb.cjdbc.controller.cache.metadata.MetadataCache;
import org.objectweb.cjdbc.controller.loadbalancer.policies.WaitForCompletionPolicy;
import org.objectweb.cjdbc.controller.loadbalancer.policies.createtable.CreateTablePolicy;
import org.objectweb.cjdbc.controller.virtualdatabase.ControllerResultSet;
import org.objectweb.cjdbc.controller.virtualdatabase.VirtualDatabase;

public class RAIDb2_RR extends RAIDb2
{
  /*
   * How the code is organized ? 1. Member variables 2. Constructor(s) 3.
   * Request handling 4. Debug/Monitoring
   */

  private int index; // index in the backend vector the Round-Robin

  /*
   * Constructors
   */

  public RAIDb2_RR(VirtualDatabase vdb,
      WaitForCompletionPolicy waitForCompletionPolicy,
      CreateTablePolicy createTablePolicy) throws SQLException
  {
    super(vdb, waitForCompletionPolicy, createTablePolicy);
    index = -1;
  }

  /*
   * Request Handling
   */

  public ControllerResultSet execReadRequest(SelectRequest request,
      MetadataCache metadataCache) throws SQLException
  {
    // Choose a backend
    try
    {
      vdb.acquireReadLockBackendLists();
    }
    catch (InterruptedException e)
    {
      String msg = Translate.get(
          "loadbalancer.backendlist.acquire.readlock.failed", e);
      logger.error(msg);
      throw new SQLException(msg);
    }

    DatabaseBackend backend = null; // The backend that will execute the query

    // Note that vdb lock is released in the finally clause of this try/catch
    // block
    try
    {
      ArrayList backends = vdb.getBackends();
      int size = backends.size();

      if (size == 0)
        throw new SQLException(Translate.get(
            "loadbalancer.execute.no.backend.available", request.getId()));

      // Take the next backend that has the needed tables
      int maxTries = size;
      int enabledBackends = 0;
      ArrayList tables = request.getFrom();

      synchronized (this)
      {
        do
        {
          index = (index + 1) % size;
          backend = (DatabaseBackend) backends.get(index);
          if (backend.isReadEnabled())
          {
            enabledBackends++;
            if (backend.hasTables(tables))
              break;
          }
          maxTries--;
        }
        while (maxTries >= 0);
      }

      if (maxTries < 0)
      { // No suitable backend found
        if (enabledBackends == 0)
          throw new NoMoreBackendException(Translate.get(
              "loadbalancer.execute.no.backend.enabled", request.getId()));
        else
          throw new SQLException(Translate.get(
              "loadbalancer.backend.no.required.tables", tables.toString()));
      }
    }
    catch (RuntimeException e)
    {
      String msg = Translate.get("loadbalancer.request.failed.on.backend",
          new String[]{request.getSQLShortForm(vdb.getSQLShortFormLength()),
              backend.getName(), e.getMessage()});
      logger.error(msg, e);
      throw new SQLException(msg);
    }
    finally
    {
      vdb.releaseReadLockBackendLists();
    }

    // Execute the request on the chosen backend
    ControllerResultSet rs = null;
    try
    {
      rs = executeRequestOnBackend(request, backend, metadataCache);
    }
    catch (UnreachableBackendException se)
    {
      // Try on another backend
      return execReadRequest(request, metadataCache);
    }
    catch (SQLException se)
    {
      String msg = Translate.get("loadbalancer.request.failed", new String[]{
          String.valueOf(request.getId()), se.getMessage()});
      if (logger.isInfoEnabled())
        logger.info(msg);
      throw new SQLException(msg);
    }
    catch (RuntimeException e)
    {
      String msg = Translate.get("loadbalancer.request.failed.on.backend",
          new String[]{request.getSQLShortForm(vdb.getSQLShortFormLength()),
              backend.getName(), e.getMessage()});
      logger.error(msg, e);
      throw new SQLException(msg);
    }

    return rs;
  }

  public ControllerResultSet execReadOnlyReadStoredProcedure(
      StoredProcedure proc, MetadataCache metadataCache) throws SQLException
  {
    // Choose a backend
    try
    {
      vdb.acquireReadLockBackendLists();
    }
    catch (InterruptedException e)
    {
      String msg = Translate.get(
          "loadbalancer.backendlist.acquire.readlock.failed", e);
      logger.error(msg);
      throw new SQLException(msg);
    }

    DatabaseBackend backend = null; // The backend that will execute the query

    // Note that vdb lock is released in the finally clause of this try/catch
    // block
    try
    {
      DatabaseBackend failedBackend = null;
      SQLException failedException = null;
      ControllerResultSet rs = null;
      do
      {
        ArrayList backends = vdb.getBackends();
        int size = backends.size();

        if (size == 0)
          throw new SQLException(Translate.get(
              "loadbalancer.execute.no.backend.available", proc.getId()));

        // Take the next backend that has the needed tables
        int maxTries = size;
        int enabledBackends = 0;

        synchronized (this)
        {
          do
          {
            index = (index + 1) % size;
            backend = (DatabaseBackend) backends.get(index);
            if (backend.isReadEnabled())
            {
              enabledBackends++;
              if ((backend != failedBackend)
                  && backend.hasStoredProcedure(proc.getProcedureName()))
                break;
            }
            maxTries--;
          }
          while (maxTries >= 0);
        }

        if (maxTries < 0)
        { // No suitable backend found
          if (enabledBackends == 0)
            throw new SQLException(Translate.get(
                "loadbalancer.execute.no.backend.enabled", proc.getId()));
          else if (failedBackend == null)
            throw new SQLException(Translate.get(
                "loadbalancer.backend.no.required.storedprocedure", proc
                    .getProcedureName()));
          else
            // Bad query, the only backend that could execute it has failed
            throw failedException;
        }

        // Execute the request on the chosen backend
        boolean toDisable = false;
        try
        {
          rs = executeStoredProcedureOnBackend(proc, backend, metadataCache);
          if (failedBackend != null)
          { // Previous backend failed
            if (logger.isWarnEnabled())
              logger.warn(Translate.get("loadbalancer.storedprocedure.status",
                  new String[]{String.valueOf(proc.getId()), backend.getName(),
                      failedBackend.getName()}));
            toDisable = true;
          }
        }
        catch (UnreachableBackendException se)
        {
          // Retry on an other backend.
          continue;
        }
        catch (SQLException se)
        {
          if (failedBackend != null)
          { // Bad query, no backend can execute it
            String msg = Translate.get(
                "loadbalancer.storedprocedure.failed.twice", new String[]{
                    String.valueOf(proc.getId()), se.getMessage()});
            if (logger.isInfoEnabled())
              logger.info(msg);
            throw new SQLException(msg);
          }
          else
          { // We are the first to fail on this query
            failedBackend = backend;
            failedException = se;
            if (logger.isInfoEnabled())
              logger.info(Translate.get(
                  "loadbalancer.storedprocedure.failed.on.backend",
                  new String[]{
                      proc.getSQLShortForm(vdb.getSQLShortFormLength()),
                      backend.getName(), se.getMessage()}));
            continue;
          }
        }

        if (toDisable)
        { // retry has succeeded and we need to disable the first node that
          // failed
          try
          {
            if (logger.isWarnEnabled())
              logger.warn(Translate.get("loadbalancer.backend.disabling",
                  failedBackend.getName()));
            failedBackend.disable();
            failedBackend.finalizeConnections();
          }
          catch (SQLException ignore)
          {
          }
          finally
          {
            failedBackend = null; // to exit the do{}while
          }
        }
      }
      while (failedBackend != null);
      return rs;
    }
    catch (RuntimeException e)
    {
      String msg = Translate.get(
          "loadbalancer.storedprocedure.failed.on.backend", new String[]{
              proc.getSQLShortForm(vdb.getSQLShortFormLength()),
              backend.getName(), e.getMessage()});
      logger.fatal(msg, e);
      throw new SQLException(msg);
    }
    finally
    {
      vdb.releaseReadLockBackendLists();
    }
  }

  /*
   * Debug/Monitoring
   */

  public String getInformation()
  {
    // We don't lock since we don't need a completely accurate value
    int size = vdb.getBackends().size();

    if (size == 0)
      return "RAIDb-2 Round-Robin Request load balancer: !!!Warning!!! No backend nodes found\n";
    else
      return "RAIDb-2 Round-Robin Request load balancer (" + size
          + " backends)\n";
  }

  public String getRaidb2Xml()
  {
    return "<" + DatabasesXmlTags.ELT_RAIDb_2_RoundRobin + "/>";
  }
}

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