Abstract KV layer options to eliminate dynamic casts to FDBTransaction

src/common/kv/ITransaction.h

@@ -31,6 +31,13 @@ static constexpr std::string_view kMetadataVersionKey = "\xff/metadataVersion";
 using Versionstamp = std::array<uint8_t, 10>;
 static_assert(sizeof(Versionstamp) == 10);
 
+enum class Priority : uint8_t {
+  MIN = 0,
+  LOW = 1,
+  HIGH = 2,
+  MAX = 3,
+};
+
 class IReadOnlyTransaction {
  public:
   virtual ~IReadOnlyTransaction() = default;
@@ -83,6 +90,8 @@ class IReadOnlyTransaction {
 
   virtual CoTryTask<void> cancel() = 0;
   virtual void reset() = 0;
+
+  virtual Result<Void> enableStaleRead() = 0;
 };
 
 class IReadWriteTransaction : public IReadOnlyTransaction {
@@ -109,6 +118,8 @@ class IReadWriteTransaction : public IReadOnlyTransaction {
 
   virtual CoTryTask<void> commit() = 0;
   virtual int64_t getCommittedVersion() = 0;
+
+  virtual Result<Void> setPriority(Priority priority) = 0;
 };
 
 struct TransactionHelper {

src/common/kv/mem/MemTransaction.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <algorithm>
+#include <boost/core/ignore_unused.hpp>
 #include <cassert>
 #include <folly/Likely.h>
 #include <folly/Synchronized.h>
@@ -245,6 +246,12 @@ class MemTransaction : public IReadWriteTransaction {
     writeConflicts_.clear();
   }
 
+  Result<Void> enableStaleRead() override { return Void{}; }
+  Result<Void> setPriority(Priority priority) override {
+    boost::ignore_unused(priority);
+    return Void{};
+  }
+
   // check txn1 updated txn2's read set
   static bool checkConflict(MemTransaction &txn1, MemTransaction &txn2) {
     std::scoped_lock<std::mutex> guard1(txn1.mutex_);

src/fdb/FDBTransaction.cc

@@ -392,6 +392,22 @@ void FDBTransaction::reset() {
   tr_.reset();
 }
 
+Result<Void> FDBTransaction::enableStaleRead() {
+  return setOption(FDBTransactionOption::FDB_TR_OPTION_USE_GRV_CACHE, {});
+}
+
+Result<Void> FDBTransaction::setPriority(Priority priority) {
+  assert(priority > PRIORITY::MIN && priority < PRIORITY::MAX);
+  switch (priority) {
+    case Priority::LOW: {
+      return setOption(FDBTransactionOption::FDB_TR_OPTION_PRIORITY_BATCH, {});
+    } break;
+    default: {
+      return Void{};
+    } break;
+  }
+}
+
 Result<Void> FDBTransaction::setOption(FDBTransactionOption option, std::string_view value) {
   fdb_error_t errcode = tr_.setOption(option, value);
   if (errcode != 0) {

src/fdb/FDBTransaction.h

@@ -40,6 +40,8 @@ class FDBTransaction : public IReadWriteTransaction {
   CoTryTask<void> commit() override;
   void reset() override;
 
+  Result<Void> enableStaleRead() override;
+  Result<Void> setPriority(Priority priority) override;
   Result<Void> setOption(FDBTransactionOption option, std::string_view value = {});
   CoTask<bool> onError(fdb_error_t errcode);
 

src/meta/components/GcManager.cc

@@ -306,9 +306,8 @@ CoTryTask<void> GcManager::GcTask::gcDirectory(GcManager &manager) {
   auto finished = false;
   auto checked = false;
   auto handler = [&](IReadWriteTransaction &txn) -> CoTryTask<void> {
-    auto fdbTxn = dynamic_cast<kv::FDBTransaction *>(&txn);
+    if (manager.config_.gc().txn_low_priority()) {
-    if (fdbTxn && manager.config_.gc().txn_low_priority()) {
+      txn.setPriority(kv::Priority::LOW);
-      fdbTxn->setOption(FDBTransactionOption::FDB_TR_OPTION_PRIORITY_BATCH, {});
     }
     if (!checked) {
       auto loadInode = co_await Inode::load(txn, taskEntry.id);
@@ -375,9 +374,8 @@ CoTryTask<void> GcManager::GcTask::gcFile(GcManager &manager) {
   XLOGF(DBG, "Gc file {}", taskEntry.id);
 
   auto load = co_await manager.runReadOnly([&](auto &txn) -> CoTryTask<std::optional<Inode>> {
-    auto fdbTxn = dynamic_cast<kv::FDBTransaction *>(&txn);
+    if (manager.config_.gc().txn_low_priority()) {
-    if (fdbTxn && manager.config_.gc().txn_low_priority()) {
+      txn.setPriority(kv::Priority::LOW);
-      fdbTxn->setOption(FDBTransactionOption::FDB_TR_OPTION_PRIORITY_BATCH, {});
     }
     if (!manager.config_.gc().check_session()) {
       co_return co_await Inode::snapshotLoad(txn, taskEntry.id);

src/meta/store/Operation.h

@@ -168,9 +168,8 @@ class OperationDriver {
     }
 
     auto grvCache = operation_.isReadOnly() && enableGrvCache;
-    if (grvCache && dynamic_cast<kv::FDBTransaction *>(txn.get())) {
+    if (grvCache) {
-      auto fdbTxn = dynamic_cast<kv::FDBTransaction *>(txn.get());
+      CO_RETURN_ON_ERROR(txn->enableStaleRead());
-      CO_RETURN_ON_ERROR(fdbTxn->setOption(FDBTransactionOption::FDB_TR_OPTION_USE_GRV_CACHE, {}));
     }
 
     Result<Rsp> result = makeError(MetaCode::kOperationTimeout);

tests/common/TestWithTransaction.cc

@@ -1,3 +1,4 @@
+#include <boost/core/ignore_unused.hpp>
 #include <folly/experimental/coro/BlockingWait.h>
 #include <gtest/gtest.h>
 #include <string_view>
@@ -65,6 +66,8 @@ class MockROTxn : public IReadOnlyTransaction {
   void reset() override {}
 
   void setReadVersion(int64_t) override {}
+
+  Result<Void> enableStaleRead() override { return Void{}; }
 };
 
 class MockRWTxn : public IReadWriteTransaction {
@@ -113,6 +116,12 @@ class MockRWTxn : public IReadWriteTransaction {
 
   void reset() override {}
 
+  Result<Void> enableStaleRead() override { return Void{}; }
+  Result<Void> setPriority(Priority priority) override {
+    boost::ignore_unused(priority);
+    return Void{};
+  }
+
  private:
   OpResultSeq &commitSeq_;
 };