ArkoSharma commented on a change in pull request #2539:
URL: https://github.com/apache/hive/pull/2539#discussion_r722350281



##########
File path: 
ql/src/java/org/apache/hadoop/hive/ql/exec/repl/ReplExternalTables.java
##########
@@ -192,64 +196,135 @@ private void dirLocationToCopy(String tableName, 
FileList fileList, Path sourceP
     fileList.add(new DirCopyWork(tableName, sourcePath, targetPath, copyMode, 
snapshotPrefix).convertToString());
   }
 
-  private SnapshotUtils.SnapshotCopyMode createSnapshotsAtSource(Path 
sourcePath, String snapshotPrefix,
-      boolean isSnapshotEnabled, HiveConf conf, 
SnapshotUtils.ReplSnapshotCount replSnapshotCount, FileList snapPathFileList,
-      ArrayList<String> prevSnaps, boolean isBootstrap) throws IOException {
+  private Map<String, SnapshotUtils.SnapshotCopyMode> 
createSnapshotsAtSource(Path sourcePath, Path targetPath, String snapshotPrefix,
+                                                                              
boolean isSnapshotEnabled, HiveConf conf, SnapshotUtils.ReplSnapshotCount 
replSnapshotCount, FileList snapPathFileList,
+                                                                              
ArrayList<String> prevSnaps, boolean isBootstrap) throws IOException {
+    Map<String, SnapshotUtils.SnapshotCopyMode> ret = new HashMap<>();
+    ret.put(snapshotPrefix, FALLBACK_COPY);
     if (!isSnapshotEnabled) {
       LOG.info("Snapshot copy not enabled for path {} Will use normal distCp 
for copying data.", sourcePath);
-      return FALLBACK_COPY;
+      return ret;
     }
+    String prefix = snapshotPrefix;
+    SnapshotUtils.SnapshotCopyMode copyMode = FALLBACK_COPY;
     DistributedFileSystem sourceDfs = SnapshotUtils.getDFS(sourcePath, conf);
     try {
-      if(isBootstrap) {
+      if(conf.getBoolVar(HiveConf.ConfVars.REPL_REUSE_SNAPSHOTS)) {
+        try {
+          FileStatus[] listing = sourceDfs.listStatus(new Path(sourcePath, 
".snapshot"));
+          for (FileStatus elem : listing) {
+            String snapShotName = elem.getPath().getName();
+            if (snapShotName.contains(OLD_SNAPSHOT)) {
+              prefix = snapShotName.substring(0, 
snapShotName.lastIndexOf(OLD_SNAPSHOT));
+              break;
+            }
+            if (snapShotName.contains(NEW_SNAPSHOT)) {
+              prefix = snapShotName.substring(0, 
snapShotName.lastIndexOf(NEW_SNAPSHOT));
+              break;
+            }
+          }
+          ret.clear();
+          ret.put(prefix, copyMode);
+          snapshotPrefix = prefix;
+        } catch (SnapshotException e) {
+          //dir not snapshottable, continue
+        }
+      }
+      boolean isFirstSnapshotAvl =
+              SnapshotUtils.isSnapshotAvailable(sourceDfs, sourcePath, 
snapshotPrefix, OLD_SNAPSHOT, conf);
+      boolean isSecondSnapAvl =
+              SnapshotUtils.isSnapshotAvailable(sourceDfs, sourcePath, 
snapshotPrefix, NEW_SNAPSHOT, conf);
+      //for bootstrap and non - failback case, use initial_copy
+      if(isBootstrap && !(!isSecondSnapAvl && isFirstSnapshotAvl)) {

Review comment:
       Considered making this change, but realised this would then require a 
similar listing and name-checking for snapshot on the target side. This can 
occur in case of reverse replication after failover with different names of src 
and tgt dbs.
   Hence decided to proceed with this implementation itself as it allows for 
identifying which snapshots are being re-used. Also makes sense to include this 
work with dump considering that in general, dump should take lesser time than 
load (except possibly cases with just external tables in db with data-copy on 
src). 




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