flush all InMemoryDataParts when wal is not enabled

src/Storages/IStorage.h

@@ -511,7 +511,7 @@ public:
     virtual void shutdown() {}
 
     /// Called before shutdown() to flush data to underlying storage
-    /// (for Buffer)
+    /// Data in memory need to be persistent
     virtual void flush() {}
 
     /// Asks table to stop executing some action identified by action_type

src/Storages/MergeTree/MergeTreeData.cpp

@@ -1525,6 +1525,24 @@ void MergeTreeData::removePartsFinally(const MergeTreeData::DataPartsVector & pa
     }
 }
 
+void MergeTreeData::flushAllInMemoryPartsIfNeeded()
+{
+    if(getSettings()->in_memory_parts_enable_wal)
+        return ;
+
+    auto metadata_snapshot = getInMemoryMetadataPtr();
+    DataPartsVector parts = getDataPartsVector();
+    for (const auto & part : parts)
+    {
+        if (auto part_in_memory = asInMemoryPart(part))
+        {
+            const auto & storage_relative_path = part_in_memory->storage.relative_data_path;
+            part_in_memory->flushToDisk(storage_relative_path, part_in_memory->relative_path, metadata_snapshot);
+        }
+    }
+
+}
+
 size_t MergeTreeData::clearOldPartsFromFilesystem(bool force)
 {
     DataPartsVector parts_to_remove = grabOldParts(force);

src/Storages/MergeTree/MergeTreeData.h

@@ -548,6 +548,9 @@ public:
     /// Removes parts from data_parts, they should be in Deleting state
     void removePartsFinally(const DataPartsVector & parts);
 
+    /// When WAL is not enabled, the InMemoryParts need to be persistent.
+    void flushAllInMemoryPartsIfNeeded();
+
     /// Delete irrelevant parts from memory and disk.
     /// If 'force' - don't wait for old_parts_lifetime.
     size_t clearOldPartsFromFilesystem(bool force = false);

src/Storages/StorageMergeTree.cpp

@@ -139,6 +139,10 @@ void StorageMergeTree::startup()
     }
 }
 
+void StorageMergeTree::flush()
+{
+    flushAllInMemoryPartsIfNeeded();
+}
 
 void StorageMergeTree::shutdown()
 {

src/Storages/StorageMergeTree.h

@@ -31,6 +31,7 @@ class StorageMergeTree final : public shared_ptr_helper<StorageMergeTree>, publi
     friend struct shared_ptr_helper<StorageMergeTree>;
 public:
     void startup() override;
+    void flush() override;
     void shutdown() override;
     ~StorageMergeTree() override;
 

tests/queries/0_stateless/02148_in_memory_part_flush.reference

@@ -0,0 +1,4 @@
+before DETACH TABLE
+500
+after DETACH TABLE
+500

tests/queries/0_stateless/02148_in_memory_part_flush.sql

@@ -0,0 +1,26 @@
+DROP TABLE IF EXISTS mem_part_flush;
+
+CREATE TABLE mem_part_flush
+(
+`key` UInt32,
+`ts` DateTime,
+`db_time` DateTime DEFAULT now()
+)
+ENGINE = MergeTree
+ORDER BY (key, ts)
+SETTINGS min_rows_for_compact_part = 1000000, min_bytes_for_compact_part = 200000000, in_memory_parts_enable_wal = 0;
+
+INSERT INTO mem_part_flush(key, ts) SELECT number % 1000, now() + intDiv(number,1000) FROM numbers(500);
+
+SELECT 'before DETACH TABLE';
+SELECT count(*) FROM mem_part_flush;
+
+DETACH TABLE mem_part_flush;
+
+ATTACH TABLE mem_part_flush;
+
+SELECT 'after DETACH TABLE';
+SELECT count(*) FROM mem_part_flush;
+
+
+DROP TABLE mem_part_flush;