fix(segment): propagate forward-store writer open failure instead of crashing (#579)

Co-authored-by: mrcs64 <9069178+mrcs64@users.noreply.github.com>

Author: mrcs64

src/db/index/segment/segment.cc

@@ -4117,6 +4117,17 @@ VectorColumnIndexer::Ptr SegmentImpl::create_vector_indexer(
 }
 
 Status SegmentImpl::init_memory_components() {
+  // Roll back any partially-created components on failure so a failed init
+  // leaves memory_store_ null (the caller's `if (!memory_store_)` retry guard
+  // depends on it) and never gets flushed on close.
+  bool committed = false;
+  AILEGO_DEFER([&]() {
+    if (!committed) {
+      memory_store_.reset();
+      memory_vector_indexers_.clear();
+      quant_memory_vector_indexers_.clear();
+    }
+  });
   // init memory block id
   auto &mem_block = segment_meta_->writing_forward_block().value();
 
@@ -4187,6 +4198,7 @@ Status SegmentImpl::init_memory_components() {
     }
   }
 
+  committed = true;
   return Status::OK();
 }
 

src/db/index/storage/memory_forward_store.cc

@@ -54,6 +54,10 @@ Status MemForwardStore::Open() {
   physic_schema_ = arrow::schema(fields);
   // Initialize file writer
   writer_ = ChunkedFileWriter::Open(path_, physic_schema_, format_);
+  if (!writer_) {
+    return Status::InternalError("failed to open forward store writer at [",
+                                 path_, "]");
+  }
   return Status::OK();
 }
 
@@ -216,6 +220,11 @@ Status MemForwardStore::flush() {
     return Status::OK();
   }
 
+  if (!writer_) {
+    return Status::InternalError(
+        "forward store writer not open, cannot flush [", path_, "]");
+  }
+
   auto result = convertToRecordBatch();
   if (!result.ok()) {
     return Status::InternalError("failed to convert cache to RecordBatch: ",

tests/db/index/storage/mem_store_test.cc

@@ -1156,3 +1156,17 @@ TEST_F(MemStoreTest, General) {
 }
 
 #endif
+
+// Regression: MemForwardStore::Open() used to ignore a failed
+// ChunkedFileWriter::Open (null writer_) and return OK, which then crashed on
+// flush(). Open() must report the failure instead.
+TEST(MemStoreOpenTest, OpenReportsErrorWhenWriterCreationFails) {
+  auto schema = GetCollectionSchema();
+  // Parent directory does not exist -> arrow FileOutputStream::Open fails ->
+  // ChunkedFileWriter::Open returns nullptr.
+  auto store = std::make_shared<MemForwardStore>(
+      schema, "/nonexistent_zvec_dir_xyz/scalar.block.0", FileFormat::IPC);
+  auto status = store->Open();
+  EXPECT_FALSE(status.ok());
+  EXPECT_EQ(store->writer_, nullptr);
+}