protobuf的报文设计

openGauss使用gRPC实现主备之间通信，但是这种reqest-response的方式，不适合我们的架构，因为我们的merge需要各节点主动发出。所以我们ZeroMQ来实现通信，并使用protobuf来序列化数据。merge消息的报文设计如下：
message MergeRequest {
message Row{
required uint64 tableExId = 1;

//获取row的tableExId
Row->GetTable()-> GetTableExId()//uint64_t
//根据tableExId获取表
fdwState = (MOTFdwStateSt*)palloc0(sizeof(MOTFdwStateSt));
fdwState->m_txnId = GetCurrentTransactionIdIfAny();
fdwState->m_currTxn = GetSafeTxn(/*fdwState->txnId*/);
fdwState->m_table = fdwState->m_currTxn->GetTableByExternalId(tableExId);

unit8 type=2;//暂时先不用
string key = 3;

bytes data= 4;

uint8_t* Row.GetData()
uint32_t Row.GetTupleSize()

uint64 startts=5;

uint64_t Row.GetStartTS()

unit64 committs=6;

uint64_t Row.GetCommitTS()

}
repeated Row row= 1;
string request_address = 2;
}