fixed

Author: sunxiaojian

paimon-core/src/main/java/org/apache/paimon/utils/BranchManager.java

@@ -105,17 +105,32 @@ public static String getBranchPath(FileIO fileIO, Path tablePath, String branchN
         return tablePath.toString() + "/branch/" + BRANCH_PREFIX + branchName;
     }
 
+    public String defaultMainBranch() {
+        Path path = new Path(tablePath, MAIN_BRANCH_FILE);
+        try {
+            if (fileIO.exists(path)) {
+                String data = fileIO.readFileUtf8(path);
+                if (!StringUtils.isBlank(data)) {
+                    return data;
+                }
+            }
+            return DEFAULT_MAIN_BRANCH;
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
     /** Return the path of a branch. */
     public Path branchPath(String branchName) {
         return new Path(getBranchPath(fileIO, tablePath, branchName));
     }
 
     public void createBranch(String branchName, String tagName) {
+        String mainBranch = defaultMainBranch();
         checkArgument(
-                !branchName.equals(DEFAULT_MAIN_BRANCH),
+                !branchName.equals(mainBranch),
                 String.format(
-                        "Branch name '%s' is the default branch and cannot be used.",
-                        DEFAULT_MAIN_BRANCH));
+                        "Branch name '%s' is the default branch and cannot be used.", mainBranch));
         checkArgument(!StringUtils.isBlank(branchName), "Branch name '%s' is blank.", branchName);
         checkArgument(!branchExists(branchName), "Branch name '%s' already exists.", branchName);
         checkArgument(tagManager.tagExists(tagName), "Tag name '%s' not exists.", tagName);
@@ -161,6 +176,12 @@ public void deleteBranch(String branchName) {
 
     /** Replace specify branch to main branch. */
     public void replaceBranch(String branchName) {
+        String mainBranch = defaultMainBranch();
+        checkArgument(
+                !branchName.equals(mainBranch),
+                String.format(
+                        "Branch name '%s' is the default main branch and cannot be replaced repeatedly.",
+                        mainBranch));
         checkArgument(!StringUtils.isBlank(branchName), "Branch name '%s' is blank.", branchName);
         checkArgument(branchExists(branchName), "Branch name '%s' not exists.", branchName);
         try {