[GitHub] [incubator-kvrocks] mapleFU commented on a diff in pull request #1287: Use the RocksDB WriteBatchWithIndex to implement the read-your-own-writes in transaction

["mapleFU (via GitHub)" <gi...@apache.org>]

mapleFU commented on code in PR #1287:
URL: https://github.com/apache/incubator-kvrocks/pull/1287#discussion_r1120328375


##########
src/storage/storage.cc:
##########
@@ -639,12 +677,33 @@ void Storage::SetIORateLimit(int64_t max_io_mb) {
 
 rocksdb::DB *Storage::GetDB() { return db_; }
 
-Status Storage::WriteToPropagateCF(const std::string &key, const std::string &value) {
-  rocksdb::WriteBatch batch;
+void Storage::BeginTxn() {
+  is_txn_mode_ = true;
+  txn_write_batch_ = std::make_unique<rocksdb::WriteBatchWithIndex>();
+}
+
+Status Storage::CommitTxn() {
+  is_txn_mode_ = false;
+  auto s = Write(write_opts_, txn_write_batch_->GetWriteBatch());
+  txn_write_batch_.reset();
+  if (s.ok()) {
+    return {Status::cOK};
+  }
+  return {Status::NotOK, s.ToString()};
+}
+
+std::shared_ptr<rocksdb::WriteBatchBase> Storage::GetWriteBatch() {

Review Comment:
   Should we name it `GetWriteBatchBase` here? And why we use shared_ptr rather than raw pointer here?



##########
src/commands/cmd_txn.cc:
##########
@@ -68,13 +69,16 @@ class CommandExec : public Commander {
       return Status::OK();
     }
 
+    auto storage = svr->storage_;
     // Reply multi length first
     conn->Reply(Redis::MultiLen(conn->GetMultiExecCommands()->size()));
     // Execute multi-exec commands
     conn->SetInExec();
+    storage->BeginTxn();
     conn->ExecuteCommands(conn->GetMultiExecCommands());
+    auto s = storage->CommitTxn();

Review Comment:
   Just a naive question. If a exception is thrown in `conn->ExecuteCommands` (I didn't review carefully, so didn't know would it throw). The transaction will never recover until another txn begin and do the thing



##########
src/storage/storage.cc:
##########
@@ -639,12 +677,33 @@ void Storage::SetIORateLimit(int64_t max_io_mb) {
 
 rocksdb::DB *Storage::GetDB() { return db_; }
 
-Status Storage::WriteToPropagateCF(const std::string &key, const std::string &value) {
-  rocksdb::WriteBatch batch;
+void Storage::BeginTxn() {
+  is_txn_mode_ = true;
+  txn_write_batch_ = std::make_unique<rocksdb::WriteBatchWithIndex>();

Review Comment:
   Does this txn has consistent read snapshot?



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