Merge pull request #7600 from azat/DirectoryMonitor-current_batch.txt-corruption

alexey-milovidov · web-flow · commit 1bfade54c25f · 2019-11-05T22:24:15.000+03:00
Write current batch for distributed send atomically (using .tmp + rename)
diff --git a/dbms/src/Storages/Distributed/DirectoryMonitor.cpp b/dbms/src/Storages/Distributed/DirectoryMonitor.cpp
@@ -355,8 +355,19 @@ struct StorageDistributedDirectoryMonitor::Batch
             /// we must try to re-send exactly the same batches.
             /// So we save contents of the current batch into the current_batch_file_path file
             /// and truncate it afterwards if all went well.
-            WriteBufferFromFile out{parent.current_batch_file_path};
-            writeText(out);
+
+            /// Temporary file is required for atomicity.
+            String tmp_file{parent.current_batch_file_path + ".tmp"};
+
+            if (Poco::File{tmp_file}.exists())
+                LOG_ERROR(parent.log, "Temporary file `" << tmp_file << "` exists. Unclean shutdown?");
+
+            {
+                WriteBufferFromFile out{tmp_file, O_WRONLY | O_TRUNC | O_CREAT};
+                writeText(out);
+            }
+
+            Poco::File{tmp_file}.renameTo(parent.current_batch_file_path);
         }
         auto timeouts = ConnectionTimeouts::getTCPTimeoutsWithFailover(parent.storage.global_context.getSettingsRef());
         auto connection = parent.pool->get(timeouts);
