[feature](read-uncommitted) Add enable_uncommitted_rowset_registry config flag

Add mutable bool config `enable_uncommitted_rowset_registry` (default true)
to control whether uncommitted rowsets are registered on BE. When disabled,
the register calls in both local and cloud rowset builders are skipped,
effectively turning off READ UNCOMMITTED visibility without restart.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: dataroaring

be/src/cloud/cloud_rowset_builder.cpp

@@ -21,6 +21,7 @@
 #include "cloud/cloud_storage_engine.h"
 #include "cloud/cloud_tablet.h"
 #include "cloud/cloud_tablet_mgr.h"
+#include "common/config.h"
 #include "olap/storage_policy.h"
 #include "olap/uncommitted_rowset_registry.h"
 
@@ -163,6 +164,9 @@ Status CloudRowsetBuilder::set_txn_related_delete_bitmap() {
 }
 
 void CloudRowsetBuilder::register_uncommitted_rowset() {
+    if (!config::enable_uncommitted_rowset_registry) {
+        return;
+    }
     auto* registry = _engine.uncommitted_rowset_registry();
     if (!registry || !_rowset) {
         return;

be/src/common/config.cpp

@@ -373,6 +373,8 @@ DEFINE_mInt32(max_percentage_of_error_disk, "100");
 DEFINE_mInt32(default_num_rows_per_column_file_block, "1024");
 // pending data policy
 DEFINE_mInt32(pending_data_expire_time_sec, "1800");
+// Enable tracking uncommitted rowsets for READ UNCOMMITTED isolation level
+DEFINE_mBool(enable_uncommitted_rowset_registry, "true");
 // Expiration time for uncommitted rowsets tracked by READ UNCOMMITTED
 DEFINE_mInt32(uncommitted_rowset_expire_sec, "30");
 // inc_rowset snapshot rs sweep time interval

be/src/common/config.h

@@ -414,6 +414,9 @@ DECLARE_mInt32(max_percentage_of_error_disk);
 DECLARE_mInt32(default_num_rows_per_column_file_block);
 // pending data policy
 DECLARE_mInt32(pending_data_expire_time_sec);
+// Enable tracking uncommitted rowsets for READ UNCOMMITTED isolation level.
+// When false, register/unregister of uncommitted rowsets is skipped.
+DECLARE_mBool(enable_uncommitted_rowset_registry);
 // Expiration time for uncommitted rowsets tracked by READ UNCOMMITTED
 DECLARE_mInt32(uncommitted_rowset_expire_sec);
 // inc_rowset snapshot rs sweep time interval

be/src/olap/rowset_builder.cpp

@@ -350,17 +350,19 @@ Status RowsetBuilder::commit_txn() {
 
     // Register uncommitted rowset for READ UNCOMMITTED visibility.
     // For MoW tablets, capture the already-computed delete bitmap.
-    if (auto* registry = _engine.uncommitted_rowset_registry()) {
-        auto entry = std::make_shared<UncommittedRowsetEntry>();
-        entry->rowset = _rowset;
-        entry->transaction_id = _req.txn_id;
-        entry->partition_id = _req.partition_id;
-        entry->tablet_id = tablet()->tablet_id();
-        entry->unique_key_merge_on_write = _tablet->enable_unique_key_merge_on_write();
-        if (entry->unique_key_merge_on_write && _delete_bitmap) {
-            entry->committed_delete_bitmap = std::make_shared<DeleteBitmap>(*_delete_bitmap);
+    if (config::enable_uncommitted_rowset_registry) {
+        if (auto* registry = _engine.uncommitted_rowset_registry()) {
+            auto entry = std::make_shared<UncommittedRowsetEntry>();
+            entry->rowset = _rowset;
+            entry->transaction_id = _req.txn_id;
+            entry->partition_id = _req.partition_id;
+            entry->tablet_id = tablet()->tablet_id();
+            entry->unique_key_merge_on_write = _tablet->enable_unique_key_merge_on_write();
+            if (entry->unique_key_merge_on_write && _delete_bitmap) {
+                entry->committed_delete_bitmap = std::make_shared<DeleteBitmap>(*_delete_bitmap);
+            }
+            registry->register_rowset(std::move(entry));
         }
-        registry->register_rowset(std::move(entry));
     }
 
     _is_committed = true;