HBASE-28568 Fix incremental backup set shrinking

hbase-backup/src/main/java/org/apache/hadoop/hbase/backup/impl/BackupAdminImpl.java

@@ -93,7 +93,6 @@ public BackupInfo getBackupInfo(String backupId) throws IOException {
   public int deleteBackups(String[] backupIds) throws IOException {
 
     int totalDeleted = 0;
-    Map<String, HashSet<TableName>> allTablesMap = new HashMap<>();
 
     boolean deleteSessionStarted;
     boolean snapshotDone;
@@ -129,20 +128,15 @@ public int deleteBackups(String[] backupIds) throws IOException {
       }
       snapshotDone = true;
       try {
+        List<String> affectedBackupRootDirs = new ArrayList<>();
         for (int i = 0; i < backupIds.length; i++) {
           BackupInfo info = sysTable.readBackupInfo(backupIds[i]);
           if (info != null) {
-            String rootDir = info.getBackupRootDir();
-            HashSet<TableName> allTables = allTablesMap.get(rootDir);
-            if (allTables == null) {
-              allTables = new HashSet<>();
-              allTablesMap.put(rootDir, allTables);
-            }
-            allTables.addAll(info.getTableNames());
+            affectedBackupRootDirs.add(info.getBackupRootDir());
             totalDeleted += deleteBackup(backupIds[i], sysTable);
           }
         }
-        finalizeDelete(allTablesMap, sysTable);
+        finalizeDelete(affectedBackupRootDirs, sysTable);
         // Finish
         sysTable.finishDeleteOperation();
         // delete snapshot
@@ -175,26 +169,23 @@ public int deleteBackups(String[] backupIds) throws IOException {
 
   /**
    * Updates incremental backup set for every backupRoot
-   * @param tablesMap map [backupRoot: {@code Set<TableName>}]
-   * @param table     backup system table
+   * @param backupRoots backupRoots for which to revise the incremental backup set
+   * @param table       backup system table
    * @throws IOException if a table operation fails
    */
-  private void finalizeDelete(Map<String, HashSet<TableName>> tablesMap, BackupSystemTable table)
+  private void finalizeDelete(List<String> backupRoots, BackupSystemTable table)
     throws IOException {
-    for (String backupRoot : tablesMap.keySet()) {
+    for (String backupRoot : backupRoots) {
       Set<TableName> incrTableSet = table.getIncrementalBackupTableSet(backupRoot);
-      Map<TableName, ArrayList<BackupInfo>> tableMap =
+      Map<TableName, List<BackupInfo>> tableMap =
         table.getBackupHistoryForTableSet(incrTableSet, backupRoot);
-      for (Map.Entry<TableName, ArrayList<BackupInfo>> entry : tableMap.entrySet()) {
-        if (entry.getValue() == null) {
-          // No more backups for a table
-          incrTableSet.remove(entry.getKey());
-        }
-      }
+
+      // Keep only the tables that are present in other backups
+      incrTableSet.retainAll(tableMap.keySet());
+
+      table.deleteIncrementalBackupTableSet(backupRoot);
       if (!incrTableSet.isEmpty()) {
         table.addIncrementalBackupTableSet(incrTableSet, backupRoot);
-      } else { // empty
-        table.deleteIncrementalBackupTableSet(backupRoot);
       }
     }
   }

hbase-backup/src/main/java/org/apache/hadoop/hbase/backup/impl/BackupSystemTable.java

@@ -839,23 +839,25 @@ public List<BackupInfo> getBackupHistoryForTable(TableName name) throws IOExcept
     return tableHistory;
   }
 
-  public Map<TableName, ArrayList<BackupInfo>> getBackupHistoryForTableSet(Set<TableName> set,
+  /**
+   * Goes through all backup history corresponding to the provided root folder, and collects all
+   * backup info mentioning each of the provided tables.
+   * @param set        the tables for which to collect the {@code BackupInfo}
+   * @param backupRoot backup destination path to retrieve backup history for
+   * @return a map containing (a subset of) the provided {@code TableName}s, mapped to a list of at
+   *         least one {@code BackupInfo}
+   * @throws IOException if getting the backup history fails
+   */
+  public Map<TableName, List<BackupInfo>> getBackupHistoryForTableSet(Set<TableName> set,
     String backupRoot) throws IOException {
     List<BackupInfo> history = getBackupHistory(backupRoot);
-    Map<TableName, ArrayList<BackupInfo>> tableHistoryMap = new HashMap<>();
-    for (Iterator<BackupInfo> iterator = history.iterator(); iterator.hasNext();) {
-      BackupInfo info = iterator.next();
-      if (!backupRoot.equals(info.getBackupRootDir())) {
-        continue;
-      }
+    Map<TableName, List<BackupInfo>> tableHistoryMap = new HashMap<>();
+    for (BackupInfo info : history) {
       List<TableName> tables = info.getTableNames();
       for (TableName tableName : tables) {
         if (set.contains(tableName)) {
-          ArrayList<BackupInfo> list = tableHistoryMap.get(tableName);
-          if (list == null) {
-            list = new ArrayList<>();
-            tableHistoryMap.put(tableName, list);
-          }
+          List<BackupInfo> list =
+            tableHistoryMap.computeIfAbsent(tableName, k -> new ArrayList<>());
           list.add(info);
         }
       }