connect to storage server failover with multi IPs

.gitignore

@@ -15,3 +15,4 @@ target
 *.conf
 *.PNG
 *.class
+*.swp

HISTORY

@@ -1,7 +1,8 @@
 
-Version 1.31  2023-12-07
+Version 1.31  2023-12-13
   * adapt to FastDFS server V6.11 for IPv6
     you must upgrade your FastDFS server to V6.11 or higher version
+  * connect to storage server failover with multi IPs
 
 Version 1.30  2023-01-29
   * support tracker server fail over

fdfs_client.conf

@@ -16,9 +16,13 @@ tracker_server = 10.0.11.247:22122
 tracker_server = 10.0.11.248:22122
 tracker_server = 10.0.11.249:22122
 
+# connect which ip address first for multi IPs of a storage server, value list:
+## tracker: connect to the ip address return by tracker server first
+## last-connected: connect to the ip address last connected first
+# default value is tracker
+connect_first_by = tracker
+
 connection_pool.enabled = true
 connection_pool.max_count_per_entry = 500
 connection_pool.max_idle_time = 3600
 connection_pool.max_wait_time_in_ms = 1000
-
-server_ipv6.enabled = false

src/main/java/org/csource/fastdfs/ClientGlobal.java

@@ -42,7 +42,7 @@ public class ClientGlobal {
   public static final String PROP_KEY_HTTP_SECRET_KEY = "fastdfs.http_secret_key";
   public static final String PROP_KEY_HTTP_TRACKER_HTTP_PORT = "fastdfs.http_tracker_http_port";
   public static final String PROP_KEY_TRACKER_SERVERS = "fastdfs.tracker_servers";
-
+  public static final String PROP_KEY_CONNECT_FIRST_BY = "fastdfs.connect_first_by";
 
   public static final String PROP_KEY_CONNECTION_POOL_ENABLED = "fastdfs.connection_pool.enabled";
   public static final String PROP_KEY_CONNECTION_POOL_MAX_COUNT_PER_ENTRY = "fastdfs.connection_pool.max_count_per_entry";
@@ -56,6 +56,9 @@ public class ClientGlobal {
   public static final String DEFAULT_HTTP_SECRET_KEY = "FastDFS1234567890";
   public static final int DEFAULT_HTTP_TRACKER_HTTP_PORT = 80;
 
+  public static final int CONNECT_FIRST_BY_TRACKER = 0;
+  public static final int CONNECT_FIRST_BY_LAST_CONNECTED = 1;
+
   public static final boolean DEFAULT_CONNECTION_POOL_ENABLED = true;
   public static final int DEFAULT_CONNECTION_POOL_MAX_COUNT_PER_ENTRY = 100;
   public static final int DEFAULT_CONNECTION_POOL_MAX_IDLE_TIME = 3600 ;//second
@@ -67,6 +70,9 @@ public class ClientGlobal {
   public static boolean g_anti_steal_token = DEFAULT_HTTP_ANTI_STEAL_TOKEN; //if anti-steal token
   public static String g_secret_key = DEFAULT_HTTP_SECRET_KEY; //generage token secret key
   public static int g_tracker_http_port = DEFAULT_HTTP_TRACKER_HTTP_PORT;
+  public static int g_connect_first_by = CONNECT_FIRST_BY_TRACKER;
+  public static boolean g_multi_storage_ips = false;
+  public static StorageAddressMap g_storages_address_map;
 
   public static boolean g_connection_pool_enabled = DEFAULT_CONNECTION_POOL_ENABLED;
   public static int g_connection_pool_max_count_per_entry = DEFAULT_CONNECTION_POOL_MAX_COUNT_PER_ENTRY;
@@ -78,6 +84,76 @@ public class ClientGlobal {
   private ClientGlobal() {
   }
 
+  private static void loadStoragsFromTracker() throws IOException, MyException {
+      TrackerClient tracker = new TrackerClient();
+      StringBuilder builder = tracker.fetchStorageIds();
+      if (builder.length() == 0) {
+          return;
+      }
+
+      System.out.println(builder.toString());
+
+      boolean without_port = true;
+      int count = 0;
+      String[] lines = builder.toString().split("\n");
+      String[] ipAddresses = new String[lines.length];
+      for (String line : lines) {
+          String[] cols = line.split(" ");
+          if (cols.length != 3) {
+              throw new MyException("invalid line: " + line);
+          }
+
+          String ipAddrs = cols[2];
+          if (ipAddrs.indexOf(',') > 0) {
+              ipAddresses[count++] = ipAddrs;
+          }
+      }
+
+      if (count == 0) {
+          return;
+      }
+
+      int startIndex;
+      if (ipAddresses[0].charAt(0) == '[') {  //IPv6
+          if ((startIndex=ipAddresses[0].indexOf(']')) < 0) {
+              throw new MyException("invalid IPv6 address: " + ipAddresses[0]);
+          }
+      } else {
+          startIndex = 0;
+      }
+      if (ipAddresses[0].indexOf(':', startIndex) > 0) {
+          without_port = false;
+      }
+
+      g_multi_storage_ips = true;
+      g_storages_address_map = new StorageAddressMap(without_port);
+      if (without_port) {
+          for (String ipAddr: ipAddresses) {
+              if (ipAddr.charAt(0) == '[') {  //IPv6
+                  ipAddr = ipAddr.substring(1, ipAddr.length() - 1);
+              }
+              String[] cols = ipAddr.split(",");
+              g_storages_address_map.puts(cols[0], cols[1]);
+          }
+      } else {
+          for (String ipPort: ipAddresses) {
+              int colonIndex = ipPort.lastIndexOf(':');
+              if (colonIndex < 0) {
+                  throw new MyException("invalid ip and port: " + ipPort);
+              }
+
+              String ipAddr = ipPort.substring(0, colonIndex);
+              int port = Integer.parseInt(ipPort.substring(colonIndex + 1));
+
+              if (ipAddr.charAt(0) == '[') {  //IPv6
+                  ipAddr = ipAddr.substring(1, ipAddr.length() - 1);
+              }
+              String[] cols = ipAddr.split(",");
+              g_storages_address_map.puts(cols[0], cols[1], port);
+          }
+      }
+  }
+
   /**
    * load global variables
    *
@@ -114,11 +190,11 @@ public class ClientGlobal {
 
     InetSocketAddress[] tracker_servers = new InetSocketAddress[szTrackerServers.length];
     for (int i = 0; i < szTrackerServers.length; i++) {
-      if(szTrackerServers[i].contains("[")){
+      if (szTrackerServers[i].contains("[")) {
         parts = new String[2];
         parts[0] = szTrackerServers[i].substring(1, szTrackerServers[i].indexOf("]"));
         parts[1] = szTrackerServers[i].substring(szTrackerServers[i].lastIndexOf(":") + 1);
-      }else {
+      } else {
         parts = szTrackerServers[i].split("\\:", 2);
       }
 
@@ -130,6 +206,11 @@ public class ClientGlobal {
     }
     g_tracker_group = new TrackerGroup(tracker_servers);
 
+    String connect_first_by = iniReader.getStrValue("connect_first_by");
+    if (connect_first_by != null && connect_first_by.equalsIgnoreCase("last-connected")) {
+        g_connect_first_by = CONNECT_FIRST_BY_LAST_CONNECTED;
+    }
+
     g_tracker_http_port = iniReader.getIntValue("http.tracker_http_port", 80);
     g_anti_steal_token = iniReader.getBoolValue("http.anti_steal_token", false);
     if (g_anti_steal_token) {
@@ -146,6 +227,8 @@ public class ClientGlobal {
     if (g_connection_pool_max_wait_time_in_ms < 0) {
       g_connection_pool_max_wait_time_in_ms = DEFAULT_CONNECTION_POOL_MAX_WAIT_TIME_IN_MS;
     }
+
+    loadStoragsFromTracker();
   }
 
   /**
@@ -183,6 +266,8 @@ public class ClientGlobal {
     String httpAntiStealTokenConf = props.getProperty(PROP_KEY_HTTP_ANTI_STEAL_TOKEN);
     String httpSecretKeyConf = props.getProperty(PROP_KEY_HTTP_SECRET_KEY);
     String httpTrackerHttpPortConf = props.getProperty(PROP_KEY_HTTP_TRACKER_HTTP_PORT);
+
+    String connectFirstBy = props.getProperty(PROP_KEY_CONNECT_FIRST_BY);
     String poolEnabled = props.getProperty(PROP_KEY_CONNECTION_POOL_ENABLED);
     String poolMaxCountPerEntry = props.getProperty(PROP_KEY_CONNECTION_POOL_MAX_COUNT_PER_ENTRY);
     String poolMaxIdleTime  = props.getProperty(PROP_KEY_CONNECTION_POOL_MAX_IDLE_TIME);
@@ -205,6 +290,10 @@ public class ClientGlobal {
     if (httpTrackerHttpPortConf != null && httpTrackerHttpPortConf.trim().length() != 0) {
       g_tracker_http_port = Integer.parseInt(httpTrackerHttpPortConf);
     }
+
+    if (connectFirstBy != null && connectFirstBy.equalsIgnoreCase("last-connected")) {
+        g_connect_first_by = CONNECT_FIRST_BY_LAST_CONNECTED;
+    }
     if (poolEnabled != null && poolEnabled.trim().length() != 0) {
       g_connection_pool_enabled = Boolean.parseBoolean(poolEnabled);
     }
@@ -217,6 +306,8 @@ public class ClientGlobal {
     if (poolMaxWaitTimeInMS != null && poolMaxWaitTimeInMS.trim().length() != 0) {
       g_connection_pool_max_wait_time_in_ms = Integer.parseInt(poolMaxWaitTimeInMS);
     }
+
+    loadStoragsFromTracker();
   }
 
   /**
@@ -360,6 +451,8 @@ public class ClientGlobal {
       + "\n  g_anti_steal_token = " + g_anti_steal_token
       + "\n  g_secret_key = " + g_secret_key
       + "\n  g_tracker_http_port = " + g_tracker_http_port
+      + "\n  g_multi_storage_ips = " + g_multi_storage_ips
+      + "\n  g_connect_first_by = " + (g_connect_first_by == CONNECT_FIRST_BY_TRACKER ? "tracker" : "last-connected")
       + "\n  g_connection_pool_enabled = " + g_connection_pool_enabled
       + "\n  g_connection_pool_max_count_per_entry = " + g_connection_pool_max_count_per_entry
       + "\n  g_connection_pool_max_idle_time(ms) = " + g_connection_pool_max_idle_time

src/main/java/org/csource/fastdfs/ProtoCommon.java

@@ -26,6 +26,7 @@ import java.util.Arrays;
  */
 public class ProtoCommon {
   public static final byte FDFS_PROTO_CMD_QUIT = 82;
+  public static final byte TRACKER_PROTO_CMD_FETCH_STORAGE_IDS = 69;
   public static final byte TRACKER_PROTO_CMD_SERVER_LIST_GROUP = 91;
   public static final byte TRACKER_PROTO_CMD_SERVER_LIST_STORAGE = 92;
   public static final byte TRACKER_PROTO_CMD_SERVER_DELETE_STORAGE = 93;
@@ -310,6 +311,23 @@ public class ProtoCommon {
     return headerInfo.errno == 0 ? true : false;
   }
 
+  /**
+   * int convert to buff (big-endian)
+   *
+   * @param n int number
+   * @return 4 bytes buff
+   */
+  public static byte[] int2buff(int n) {
+      byte[] bs;
+
+      bs = new byte[4];
+      bs[0] = (byte) ((n >> 24) & 0xFF);
+      bs[1] = (byte) ((n >> 16) & 0xFF);
+      bs[2] = (byte) ((n >> 8) & 0xFF);
+      bs[3] = (byte) (n & 0xFF);
+      return bs;
+  }
+
   /**
    * long convert to buff (big-endian)
    *
@@ -317,19 +335,18 @@ public class ProtoCommon {
    * @return 8 bytes buff
    */
   public static byte[] long2buff(long n) {
-    byte[] bs;
+      byte[] bs;
 
-    bs = new byte[8];
+      bs = new byte[8];
-    bs[0] = (byte) ((n >> 56) & 0xFF);
+      bs[0] = (byte) ((n >> 56) & 0xFF);
-    bs[1] = (byte) ((n >> 48) & 0xFF);
+      bs[1] = (byte) ((n >> 48) & 0xFF);
-    bs[2] = (byte) ((n >> 40) & 0xFF);
+      bs[2] = (byte) ((n >> 40) & 0xFF);
-    bs[3] = (byte) ((n >> 32) & 0xFF);
+      bs[3] = (byte) ((n >> 32) & 0xFF);
-    bs[4] = (byte) ((n >> 24) & 0xFF);
+      bs[4] = (byte) ((n >> 24) & 0xFF);
-    bs[5] = (byte) ((n >> 16) & 0xFF);
+      bs[5] = (byte) ((n >> 16) & 0xFF);
-    bs[6] = (byte) ((n >> 8) & 0xFF);
+      bs[6] = (byte) ((n >> 8) & 0xFF);
-    bs[7] = (byte) (n & 0xFF);
+      bs[7] = (byte) (n & 0xFF);
-
+      return bs;
-    return bs;
   }
 
   /**

src/main/java/org/csource/fastdfs/StorageAddressMap.java

@@ -0,0 +1,62 @@
+/**
+ * Copyright (C) 2023 Happy Fish / YuQing
+ * <p>
+ * FastDFS Java Client may be copied only under the terms of the GNU Lesser
+ * General Public License (LGPL).
+ * Please visit the FastDFS Home Page https://github.com/happyfish100/fastdfs for more detail.
+ */
+
+package org.csource.fastdfs;
+
+import java.util.HashMap;
+import java.net.InetSocketAddress;
+
+/**
+ * Storage Server Address Map
+ *
+ * @author Happy Fish / YuQing
+ * @version Version 1.31
+ */
+public class StorageAddressMap {
+
+    protected boolean without_port;
+    protected HashMap<String, InetSocketAddress> storages;
+
+    public StorageAddressMap(boolean without_port) {
+        this.without_port = without_port;
+        this.storages = new HashMap<String, InetSocketAddress>();
+    }
+
+    protected String getKey(String ipAddr, int port) {
+        return ipAddr + "@" + port;
+    }
+
+    public void puts(String srcIpAddr, String destIpAddr, int port) {
+        storages.put(this.getKey(srcIpAddr, port),
+                new InetSocketAddress(destIpAddr, port));
+        storages.put(this.getKey(destIpAddr, port),
+                new InetSocketAddress(srcIpAddr, port));
+    }
+
+    public void puts(String srcIpAddr, String destIpAddr) {
+        storages.put(srcIpAddr, new InetSocketAddress(destIpAddr, 0));
+        storages.put(destIpAddr, new InetSocketAddress(srcIpAddr, 0));
+    }
+
+    public InetSocketAddress get(String ipAddr, int port) {
+        if (this.without_port) {
+            InetSocketAddress sockAddr;
+            if ((sockAddr=storages.get(ipAddr)) == null) {
+                return null;
+            }
+
+            return new InetSocketAddress(sockAddr.getAddress(), port);
+        } else {
+            return storages.get(this.getKey(ipAddr, port));
+        }
+    }
+
+    public InetSocketAddress get(InetSocketAddress sockAddr) {
+        return this.get(sockAddr.getAddress().getHostAddress(), sockAddr.getPort());
+    }
+}

src/main/java/org/csource/fastdfs/StorageClient.java

@@ -847,7 +847,6 @@ public class StorageClient {
             throw ex;
         } finally {
             releaseConnection(connection, bNewStorageServer);
-
         }
     }
 

src/main/java/org/csource/fastdfs/StorageServer.java

@@ -9,6 +9,9 @@
 package org.csource.fastdfs;
 
 import java.io.IOException;
+import java.util.Hashtable;
+import org.csource.common.MyException;
+import org.csource.fastdfs.pool.Connection;
 import java.net.InetSocketAddress;
 
 /**
@@ -18,40 +21,112 @@ import java.net.InetSocketAddress;
  * @version Version 1.11
  */
 public class StorageServer extends TrackerServer {
-  protected int store_path_index = 0;
+    protected int store_path_index = 0;
 
-  /**
+    protected static Hashtable<String, InetSocketAddress> sockAddressCache = new Hashtable<String, InetSocketAddress>();
-   * Constructor
-   *
-   * @param ip_addr    the ip address of storage server
-   * @param port       the port of storage server
-   * @param store_path the store path index on the storage server
-   */
-  public StorageServer(String ip_addr, int port, int store_path) throws IOException {
-    super(new InetSocketAddress(ip_addr, port));
-    this.store_path_index = store_path;
-  }
 
-  /**
+    /**
-   * Constructor
+     * Constructor
-   *
+     *
-   * @param ip_addr    the ip address of storage server
+     * @param ip_addr    the ip address of storage server
-   * @param port       the port of storage server
+     * @param port       the port of storage server
-   * @param store_path the store path index on the storage server
+     * @param store_path the store path index on the storage server
-   */
+     */
-  public StorageServer(String ip_addr, int port, byte store_path) throws IOException {
+    public StorageServer(String ip_addr, int port, int store_path) throws IOException {
-    super(new InetSocketAddress(ip_addr, port));
+        super(new InetSocketAddress(ip_addr, port));
-    if (store_path < 0) {
+        this.store_path_index = store_path;
-      this.store_path_index = 256 + store_path;
-    } else {
-      this.store_path_index = store_path;
     }
-  }
 
-  /**
+    /**
-   * @return the store path index on the storage server
+     * Constructor
-   */
+     *
-  public int getStorePathIndex() {
+     * @param ip_addr    the ip address of storage server
-    return this.store_path_index;
+     * @param port       the port of storage server
-  }
+     * @param store_path the store path index on the storage server
+     */
+    public StorageServer(String ip_addr, int port, byte store_path) throws IOException {
+        super(new InetSocketAddress(ip_addr, port));
+        if (store_path < 0) {
+            this.store_path_index = 256 + store_path;
+        } else {
+            this.store_path_index = store_path;
+        }
+    }
+
+    /**
+     * @return the store path index on the storage server
+     */
+    public int getStorePathIndex() {
+        return this.store_path_index;
+    }
+
+    public Connection getConnection() throws MyException, IOException {
+        Connection connection;
+        InetSocketAddress sockAddr;
+        MyException myException = null;
+        IOException ioException = null;
+
+        if (!ClientGlobal.g_multi_storage_ips) {
+            return super.getConnection();
+        }
+
+        if (ClientGlobal.g_connect_first_by == ClientGlobal.CONNECT_FIRST_BY_TRACKER) {
+            try {
+                if ((connection=super.getConnection()) != null) {
+                    return connection;
+                }
+            } catch (MyException ex1) {
+                myException = ex1;
+            } catch (IOException ex2) {
+                ioException = ex2;
+            }
+
+            sockAddr = ClientGlobal.g_storages_address_map.get(this.inetSockAddr);
+            if (sockAddr != null) {
+                return super.getConnection(sockAddr);
+            } else if (myException != null) {
+                throw myException;
+            } else if (ioException != null) {
+                throw ioException;
+            }
+        } else {
+            String key = this.inetSockAddr.getAddress().getHostAddress() +
+                "@" + this.inetSockAddr.getPort();
+            sockAddr = sockAddressCache.get(key);
+            try {
+                if (sockAddr == null) {
+                    sockAddr = this.inetSockAddr;
+                    if ((connection=super.getConnection(sockAddr)) != null) {
+                        sockAddressCache.put(key, sockAddr);
+                        return connection;
+                    }
+                } else {
+                    if ((connection=super.getConnection(sockAddr)) != null) {
+                        return connection;
+                    }
+                }
+            } catch (MyException ex1) {
+                myException = ex1;
+            } catch (IOException ex2) {
+                ioException = ex2;
+            }
+
+            //retry another ip address
+            if ((sockAddr=ClientGlobal.g_storages_address_map.get(sockAddr)) == null) {
+                if (myException != null) {
+                    throw myException;
+                } else if (ioException != null) {
+                    throw ioException;
+                }
+                return null;
+            }
+
+            if ((connection=super.getConnection(sockAddr)) != null) {
+                sockAddressCache.put(key, sockAddr);
+                return connection;
+            }
+        }
+
+        return null;
+    }
 }

src/main/java/org/csource/fastdfs/TrackerClient.java

@@ -735,8 +735,9 @@ public class TrackerClient {
      * @param storageIpAddr the storage server ip address
      * @return true for success, false for fail
      */
-    public boolean deleteStorage(TrackerGroup trackerGroup,
+    public boolean deleteStorage(TrackerGroup trackerGroup, String groupName,
-                                 String groupName, String storageIpAddr) throws IOException, MyException {
+            String storageIpAddr) throws IOException, MyException
+    {
         int serverIndex;
         int notFoundCount;
         TrackerServer trackerServer;
@@ -805,4 +806,78 @@ public class TrackerClient {
 
         return this.errno == 0;
     }
+
+    /**
+     * query storage server to upload file
+     *
+     * @param trackerServer the tracker server
+     * @param groupName     the group name to upload file to, can be empty
+     * @return storage server object, return null if fail
+     */
+    public StringBuilder fetchStorageIds() throws IOException, MyException {
+        byte[] header;
+        int offset = 0;
+        int length;
+        int total_count;
+        int current_count;
+
+        Connection connection = getConnection(null);
+        try {
+            OutputStream out = connection.getOutputStream();
+            StringBuilder builder = new StringBuilder();
+
+            header = ProtoCommon.packHeader(ProtoCommon.TRACKER_PROTO_CMD_FETCH_STORAGE_IDS, 5, (byte)0);
+            byte[] wholePkg = new byte[header.length + 5];
+            System.arraycopy(header, 0, wholePkg, 0, header.length);
+            wholePkg[wholePkg.length - 1] = 1;
+            do {
+                byte[] bs = ProtoCommon.int2buff(offset);
+                System.arraycopy(bs, 0, wholePkg, header.length, bs.length);
+                out.write(wholePkg);
+
+                ProtoCommon.RecvPackageInfo pkgInfo = ProtoCommon.recvPackage(
+                        connection.getInputStream(),
+                        ProtoCommon.TRACKER_PROTO_CMD_RESP, -1);
+                this.errno = pkgInfo.errno;
+                if (pkgInfo.errno != 0) {
+                    return null;
+                }
+
+                if (pkgInfo.body.length < 8) {
+                    throw new MyException("invalid body length: " + pkgInfo.body.length);
+                }
+
+                total_count = ProtoCommon.buff2int(pkgInfo.body, 0);
+                current_count = ProtoCommon.buff2int(pkgInfo.body, 4);
+                if (current_count < 0) {
+                    throw new MyException("invalid current count: " + current_count);
+                }
+
+                length = pkgInfo.body.length - 8;
+                if (length == 0) {
+                    break;
+                }
+
+                bs = new byte[length];
+                System.arraycopy(pkgInfo.body, 8, bs, 0, length);
+                builder.append(new String(bs, ClientGlobal.g_charset));
+
+                offset += current_count;
+            } while (offset < total_count);
+
+            return builder;
+        } catch (IOException e) {
+            try {
+                connection.close();
+            } finally {
+                connection = null;
+            }
+            throw e;
+        } finally {
+            if (connection != null) {
+                connection.release();
+            }
+        }
+    }
+
 }

src/main/java/org/csource/fastdfs/TrackerServer.java

@@ -37,15 +37,20 @@ public class TrackerServer {
         this.index = index;
     }
 
-    public Connection getConnection() throws MyException, IOException {
+    protected Connection getConnection(InetSocketAddress sockAddr) throws MyException, IOException {
         Connection connection;
         if (ClientGlobal.g_connection_pool_enabled) {
-            connection = ConnectionPool.getConnection(this.inetSockAddr);
+            connection = ConnectionPool.getConnection(sockAddr);
         } else {
-            connection = ConnectionFactory.create(this.inetSockAddr);
+            connection = ConnectionFactory.create(sockAddr);
         }
         return connection;
     }
+
+    public Connection getConnection() throws MyException, IOException {
+        return this.getConnection(this.inetSockAddr);
+    }
+
     /**
      * get the server info
      *

src/main/resources/fastdfs-client.properties.sample

@@ -18,6 +18,14 @@ fastdfs.http_tracker_http_port = 80
 #
 fastdfs.tracker_servers = 185.245.40.70:22122
 
+
+# connect which ip address first for multi IPs of a storage server, value list:
+## tracker: connect to the ip address return by tracker server first
+## last-connected: connect to the ip address last connected first
+# default value is tracker
+fastdfs.connect_first_by = tracker
+
+
 ## Whether to open the connection pool, if not, create a new connection every time
 fastdfs.connection_pool.enabled = true
 

src/main/resources/fdfs_client.conf.sample

@@ -15,6 +15,14 @@ http.secret_key = FastDFS1234567890
 tracker_server = 10.0.11.243:22122
 tracker_server = 10.0.11.244:22122
 
+
+# connect which ip address first for multi IPs of a storage server, value list:
+## tracker: connect to the ip address return by tracker server first
+## last-connected: connect to the ip address last connected first
+# default value is tracker
+connect_first_by = tracker
+
+
 connection_pool.enabled = true
 connection_pool.max_count_per_entry = 500
 connection_pool.max_idle_time = 3600