feat(config): add txn_context_enabled to allow to enable the transa…

…ction feature (apache#2506)

Co-authored-by: mwish <maplewish117@gmail.com>

kvrocks.conf

@@ -335,6 +335,20 @@ json-max-nesting-depth 1024
 # Default: json
 json-storage-format json
 
+# Whether to enable transactional mode engine::Context.
+#
+# If enabled, is_txn_mode in engine::Context will be set properly,
+# which is expected to improve the consistency of commands.
+# If disabled, is_txn_mode in engine::Context will be set to false,
+# making engine::Context equivalent to engine::Storage.
+#
+# NOTE: This is an experimental feature. If you find errors, performance degradation,
+# excessive memory usage, excessive disk I/O, etc. after enabling it, please try disabling it.
+# At the same time, we welcome feedback on related issues to help iterative improvements.
+# 
+# Default: no
+txn-context-enabled no
+
 # In some scenarios client connections can hog up memory leading to OOM
 # errors or data eviction. To avoid this we can cap the accumulated memory
 # used by all client connections (all pubsub and normal clients). Once we

src/config/config.cc

@@ -193,6 +193,7 @@ Config::Config() {
  {"json-max-nesting-depth", false, new IntField(&json_max_nesting_depth, 1024, 0, INT_MAX)},
  {"json-storage-format", false,
  new EnumField<JsonStorageFormat>(&json_storage_format, json_storage_formats, JsonStorageFormat::JSON)},
+ {"txn-context-enabled", true, new YesNoField(&txn_context_enabled, false)},
  {"maxmemory-clients", false, new IntWithUnitField<uint64_t>(&max_memory_clients, "0", 0, UINT64_MAX)},
 
  /* rocksdb options */

src/config/config.h

@@ -168,6 +168,9 @@ struct Config {
  int json_max_nesting_depth = 1024;
  JsonStorageFormat json_storage_format = JsonStorageFormat::JSON;
 
+ // Enable transactional mode in engine::Context
+ bool txn_context_enabled = false;
+
  uint64_t max_memory_clients = 0;
 
  struct RocksDB {

src/storage/storage.h

@@ -388,7 +388,8 @@ struct Context {
  std::unique_ptr<rocksdb::WriteBatchWithIndex> batch = nullptr;
 
  /// is_txn_mode is used to determine whether the current Context is in transactional mode,
- /// if it is not transactional mode, then Context is equivalent to a Storage
+ /// if it is not transactional mode, then Context is equivalent to a Storage.
+ /// If the configuration of txn-context-enabled is no, it is false.
  bool is_txn_mode = true;
 
  /// NoTransactionContext returns a Context with a is_txn_mode of false
@@ -409,6 +410,10 @@ struct Context {
  /// TODO: Change it to defer getting the context, and the snapshot is pinned after the first read operation
  explicit Context(engine::Storage *storage) : storage(storage) {
  auto guard = storage->ReadLockGuard();
+ if (!storage->GetConfig()->txn_context_enabled) {
+ is_txn_mode = false;
+ return;
+ }
  snapshot = storage->GetDB()->GetSnapshot(); // NOLINT
  }
  ~Context() {