Optimize seek leader store logic (tikv#335)

Signed-off-by: marsishandsome <marsishandsome@gmail.com>

Author: birdstorm

src/main/java/org/tikv/common/region/AbstractRegionStoreClient.java

@@ -39,7 +39,6 @@
 import org.tikv.common.log.SlowLogEmptyImpl;
 import org.tikv.common.log.SlowLogSpan;
 import org.tikv.common.util.ChannelFactory;
-import org.tikv.common.util.Pair;
 import org.tikv.kvproto.Kvrpcpb;
 import org.tikv.kvproto.Metapb;
 import org.tikv.kvproto.TikvGrpc;
@@ -143,15 +142,6 @@ public boolean onStoreUnreachable(SlowLog slowLog) {
       return true;
     }
 
-    if (store.getProxyStore() == null && store.isReachable()) {
-      if (store.isReachable()) {
-        logger.info(
-            String.format(
-                "store[%d] for region[%d] is reachable, retry", store.getId(), region.getId()));
-        return true;
-      }
-    }
-
     // seek an available leader store to send request
     Boolean result = seekLeaderStore(slowLog);
     if (result != null) {
@@ -206,26 +196,8 @@ private Boolean seekLeaderStore(SlowLog slowLog) {
 
       logger.info(String.format("try switch leader: region[%d]", region.getId()));
 
-      Pair<Metapb.Peer, Boolean> pair = switchLeaderStore();
-      Metapb.Peer peer = pair.first;
-      boolean exceptionEncountered = pair.second;
-      if (peer == null) {
-        if (!exceptionEncountered) {
-          // all response returned normally, the leader is not elected, just wait until it is ready.
-          logger.info(
-              String.format(
-                  "leader for region[%d] is not elected, just wait until it is ready",
-                  region.getId()));
-          return true;
-        } else {
-          // no leader found, some response does not return normally, there may be network
-          // partition.
-          logger.warn(
-              String.format(
-                  "leader for region[%d] is not found, it is possible that network partition occurred",
-                  region.getId()));
-        }
-      } else {
+      Metapb.Peer peer = switchLeaderStore();
+      if (peer != null) {
         // we found a leader
         TiStore currentLeaderStore = regionManager.getStoreById(peer.getStoreId());
         if (currentLeaderStore.isReachable()) {
@@ -240,6 +212,12 @@ private Boolean seekLeaderStore(SlowLog slowLog) {
           updateClientStub();
           return true;
         }
+      } else {
+        // no leader found, some response does not return normally, there may be network partition.
+        logger.warn(
+            String.format(
+                "leader for region[%d] is not found, it is possible that network partition occurred",
+                region.getId()));
       }
     } finally {
       switchLeaderDurationTimer.observeDuration();
@@ -272,7 +250,7 @@ private boolean seekProxyStore(SlowLog slowLog) {
   }
 
   // first: leader peer, second: true if any responses returned with grpc error
-  private Pair<Metapb.Peer, Boolean> switchLeaderStore() {
+  private Metapb.Peer switchLeaderStore() {
     List<SwitchLeaderTask> responses = new LinkedList<>();
     for (Metapb.Peer peer : region.getFollowerList()) {
       ByteString key = region.getStartKey();
@@ -290,7 +268,6 @@ private Pair<Metapb.Peer, Boolean> switchLeaderStore() {
       ListenableFuture<Kvrpcpb.RawGetResponse> task = stub.rawGet(rawGetRequest);
       responses.add(new SwitchLeaderTask(task, peer));
     }
-    boolean exceptionEncountered = false;
     while (true) {
       try {
         Thread.sleep(2);
@@ -310,15 +287,14 @@ private Pair<Metapb.Peer, Boolean> switchLeaderStore() {
               // the peer is leader
               logger.info(
                   String.format("rawGet response indicates peer[%d] is leader", task.peer.getId()));
-              return Pair.create(task.peer, exceptionEncountered);
+              return task.peer;
             }
           }
         } catch (Exception ignored) {
-          exceptionEncountered = true;
         }
       }
       if (unfinished.isEmpty()) {
-        return Pair.create(null, exceptionEncountered);
+        return null;
       }
       responses = unfinished;
     }