From b5495d5467ddc923314af36812c753217b24a657 Mon Sep 17 00:00:00 2001
From: mrcs64 <9069178+mrcs64@users.noreply.github.com>
Date: Fri, 10 Jul 2026 08:09:34 +0200
Subject: [PATCH 1/2] fix(segment): propagate forward-store writer open failure
 instead of crashing

MemForwardStore::Open() stored the result of ChunkedFileWriter::Open() (a
unique_ptr that is null when the underlying arrow FileOutputStream cannot be
created, e.g. under file-descriptor pressure from many concurrent collection
opens) but returned Status::OK() unconditionally. The failure was swallowed:
the store reported success with a null writer_, and a later flush()/close()
dereferenced it, crashing with SIGSEGV at memory_forward_store.cc:283.

init_memory_components() also assigned memory_store_ to the member before
Open() succeeded, so a failed init left a non-null, half-built memory_store_
that satisfied the `if (!memory_store_)` re-init guard and got flushed on close.

- MemForwardStore::Open(): return an error when the writer cannot be opened.
- MemForwardStore::flush(): guard against a null writer_ before writing.
- SegmentImpl::init_memory_components(): roll back partial components on failure
  via AILEGO_DEFER so a failed init leaves memory_store_ null.

Adds a mem_store_test case asserting Open() reports an error when the writer
cannot be created.
---
 src/db/index/segment/segment.cc              | 12 ++++++++++++
 src/db/index/storage/memory_forward_store.cc |  9 +++++++++
 tests/db/index/storage/mem_store_test.cc     | 14 ++++++++++++++
 3 files changed, 35 insertions(+)

diff --git a/src/db/index/segment/segment.cc b/src/db/index/segment/segment.cc
index e21ececa2..246ddded5 100644
--- a/src/db/index/segment/segment.cc
+++ b/src/db/index/segment/segment.cc
@@ -4116,6 +4116,17 @@ 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();
 
@@ -4186,6 +4197,7 @@ Status SegmentImpl::init_memory_components() {
     }
   }
 
+  committed = true;
   return Status::OK();
 }
 
diff --git a/src/db/index/storage/memory_forward_store.cc b/src/db/index/storage/memory_forward_store.cc
index 94a6aa33a..40ce7b8f7 100644
--- a/src/db/index/storage/memory_forward_store.cc
+++ b/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: ",
diff --git a/tests/db/index/storage/mem_store_test.cc b/tests/db/index/storage/mem_store_test.cc
index da0bd64be..d8ca52bc1 100644
--- a/tests/db/index/storage/mem_store_test.cc
+++ b/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);
+}

From 854513333022b992aa7478938f0ed73c03c6c260 Mon Sep 17 00:00:00 2001
From: mrcs64 <9069178+mrcs64@users.noreply.github.com>
Date: Thu, 16 Jul 2026 08:22:07 +0200
Subject: [PATCH 2/2] style(segment): satisfy clang-format on forward-store
 error path

---
 src/db/index/storage/memory_forward_store.cc | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/db/index/storage/memory_forward_store.cc b/src/db/index/storage/memory_forward_store.cc
index 40ce7b8f7..268a7c581 100644
--- a/src/db/index/storage/memory_forward_store.cc
+++ b/src/db/index/storage/memory_forward_store.cc
@@ -55,8 +55,8 @@ Status MemForwardStore::Open() {
   // 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::InternalError("failed to open forward store writer at [",
+                                 path_, "]");
   }
   return Status::OK();
 }