[Remote Store] Add check for byte lag in time lag calculation (#12565)

Signed-off-by: Ashish Singh <ssashish@amazon.com>

Author: ashking94

server/src/main/java/org/opensearch/index/remote/RemoteSegmentTransferTracker.java

@@ -260,7 +260,7 @@ public long getRefreshSeqNoLag() {
     }
 
     public long getTimeMsLag() {
-        if (remoteRefreshTimeMs == localRefreshTimeMs) {
+        if (remoteRefreshTimeMs == localRefreshTimeMs || bytesLag == 0) {
             return 0;
         }
         return currentTimeMsUsingSystemNanos() - remoteRefreshStartTimeMs;

server/src/test/java/org/opensearch/index/remote/RemoteSegmentTransferTrackerTests.java

@@ -21,6 +21,7 @@
 
 import java.io.IOException;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 
 import static org.opensearch.index.remote.RemoteSegmentTransferTracker.currentTimeMsUsingSystemNanos;
@@ -149,6 +150,7 @@ public void testComputeTimeLagOnUpdate() throws InterruptedException {
         Thread.sleep(1);
         transferTracker.updateLocalRefreshTimeMs(currentTimeMsUsingSystemNanos());
 
+        transferTracker.updateLatestLocalFileNameLengthMap(List.of("test"), k -> 1L);
         // Sleep for 100ms and then the lag should be within 100ms +/- 20ms
         Thread.sleep(100);
         assertTrue(Math.abs(transferTracker.getTimeMsLag() - 100) <= 20);

server/src/test/java/org/opensearch/index/remote/RemoteStorePressureServiceTests.java

@@ -19,6 +19,7 @@
 import org.opensearch.threadpool.ThreadPool;
 
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 import java.util.concurrent.atomic.AtomicLong;
 import java.util.regex.Matcher;
@@ -100,6 +101,7 @@ public void testValidateSegmentUploadLag() throws InterruptedException {
         while (currentTimeMsUsingSystemNanos() - localRefreshTimeMs <= 20 * avg) {
             Thread.sleep((long) (4 * avg));
         }
+        pressureTracker.updateLatestLocalFileNameLengthMap(List.of("test"), k -> 1L);
         Exception e = assertThrows(OpenSearchRejectedExecutionException.class, () -> pressureService.validateSegmentsUploadLag(shardId));
         String regex = "^rejected execution on primary shard:\\[index]\\[0] due to remote segments lagging behind "
             + "local segments.time_lag:[0-9]{2,3} ms dynamic_time_lag_threshold:95\\.0 ms$";