Fix panic when region is not found on TiFlash's side in tryFlushData

dbms/src/Storages/Transaction/KVStore.cpp

@@ -338,6 +338,15 @@ bool KVStore::tryFlushRegionData(UInt64 region_id, bool try_until_succeed, TMTCo
 {
     auto region_task_lock = region_manager.genRegionTaskLock(region_id);
     const RegionPtr curr_region_ptr = getRegion(region_id);
+    if (curr_region_ptr == nullptr)
+    {
+        /// If we can't find region here, we return true so proxy can trigger a CompactLog.
+        /// The triggered CompactLog will be handled by `handleUselessAdminRaftCmd`,
+        /// and result in a `EngineStoreApplyRes::NotFound`.
+        /// Proxy will print `region not found in engine-store, maybe have exec `RemoveNode` first`.
+        LOG_FMT_WARNING(log, "region {} [index: {}, term {}], not exist when flushing, maybe have exec `RemoveNode` first", region_id, index, term);
+        return true;
+    }
     return canFlushRegionDataImpl(curr_region_ptr, true, try_until_succeed, tmt, region_task_lock, index, term);
 }
 

dbms/src/Storages/Transaction/tests/gtest_kvstore.cpp

@@ -1242,6 +1242,8 @@ void RegionKVStoreTest::testKVStore()
         ASSERT_EQ(kvs.needFlushRegionData(19, ctx.getTMTContext()), true);
         // Force flush until succeed only for testing.
         ASSERT_EQ(kvs.tryFlushRegionData(19, true, ctx.getTMTContext(), 0, 0), true);
+        // Non existing region.
+        ASSERT_EQ(kvs.tryFlushRegionData(1999, true, ctx.getTMTContext(), 0, 0), true);
     }
 }