Ignore unreachable nodes when detecting the local DC

core/src/main/java/tech/ydb/core/impl/pool/PriorityPicker.java

@@ -90,14 +90,25 @@ static String detectLocalDC(List<EndpointRecord> endpoints, Ticker ticker) {
 
             int nodeSize = Math.min(nodes.size(), DETECT_DC_NODE_SIZE);
             long tcpPing = 0;
+            int reachableCount = 0;
 
             for (EndpointRecord node : nodes.subList(0, nodeSize)) {
-                long currentPing = tcpPing(new InetSocketAddress(node.getHost(), node.getPort()), ticker);
-                logger.debug("Address: {}, port: {}, nanos ping: {}", node.getHost(), node.getPort(), currentPing);
-                tcpPing += currentPing;
+                try {
+                    long currentPing = tcpPing(new InetSocketAddress(node.getHost(), node.getPort()), ticker);
+                    logger.debug("{}, nanos ping: {}", node, currentPing);
+                    tcpPing += currentPing;
+                    reachableCount++;
+                } catch (IOException ex) {
+                    logger.warn("{} is not reachable with error {}", node, ex.getMessage());
+                }
             }
 
-            tcpPing /= nodeSize;
+            if (reachableCount == 0) {
+                logger.debug("No reachable nodes in {}, skip it", dc);
+                continue;
+            }
+
+            tcpPing /= reachableCount;
 
             if (minPing > tcpPing) {
                 minPing = tcpPing;
@@ -108,14 +119,11 @@ static String detectLocalDC(List<EndpointRecord> endpoints, Ticker ticker) {
         return localDC;
     }
 
-    private static long tcpPing(InetSocketAddress socketAddress, Ticker ticker) {
+    private static long tcpPing(InetSocketAddress socketAddress, Ticker ticker) throws IOException {
         try (Socket socket = SocketFactory.getDefault().createSocket()) {
-            final long startConnection = ticker.read();
+            long started = ticker.read();
             socket.connect(socketAddress, DETECT_DC_TCP_PING_TIMEOUT_MS);
-            final long stopConnection = ticker.read();
-            return stopConnection - startConnection;
-        } catch (IOException e) {
-            return Long.MAX_VALUE;
+            return ticker.read() - started;
         }
     }
 }

core/src/test/java/tech/ydb/core/impl/pool/PriorityPickerTest.java

@@ -2,6 +2,7 @@
 
 import java.io.IOException;
 import java.net.ServerSocket;
+import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 import java.util.stream.Collectors;
@@ -108,4 +109,37 @@ public void detectLocalDCTest() {
             throw new RuntimeException(e);
         }
     }
+
+    @Test
+    public void detectLocalDCWithUnreachableNodesTest() throws IOException {
+        int closedPort;
+
+        try (ServerSocket socket = ServerSocketFactory.getDefault().createServerSocket(0)) {
+            closedPort = socket.getLocalPort();
+        }
+
+        // every successful probe takes 10 nanos
+        Ticker ticker = new Ticker() {
+            private long now = 0;
+
+            @Override
+            public long read() {
+                now += 10;
+                return now;
+            }
+        };
+
+        try (ServerSocket serverSocket = ServerSocketFactory.getDefault().createServerSocket(0)) {
+            int openPort = serverSocket.getLocalPort();
+
+            List<EndpointRecord> records = Arrays.asList(
+                    new EndpointRecord("localhost", closedPort, 1, "DOWN", null),
+                    new EndpointRecord("localhost", closedPort, 2, "DOWN", null),
+                    new EndpointRecord("localhost", openPort, 3, "UP", null)
+            );
+
+            // failed probes of DOWN must not overflow into a negative, i.e. the best, ping
+            Assert.assertEquals("UP", PriorityPicker.detectLocalDC(records, ticker));
+        }
+    }
 }