1. 代码版本说明

源码分析基于4.2.0版本。

2. 核心逻辑执行路径

本节内容，只把impala be,fe 执行的调用主路径做一个梳理。fe模块的sql语法解析,语义解析,查询计划生成;be模块的资源调度，查询任务执行在后续的内容中进行展开分析。

3. 主进程入口

be/src/service/daemon-main.cc 程序入口。impalad,catalogd,statestored为同一个二进制程序，根据启动参数的类型，选择启动不通的角色功能。后续代码分析，以impalad的执行逻辑来分析。

int main(int argc, char** argv) {  
path cmd_line_path(argv[0]);  
string daemon = cmd_line_path.filename().string();  
if (daemon == "statestored") {  
return StatestoredMain(argc, argv);  
}  
  
if (daemon == "impalad") {  
return ImpaladMain(argc, argv);  
}  
  
if (daemon == "catalogd") {  
return CatalogdMain(argc, argv);  
}  
  
if (daemon == "admissiond") {  
return AdmissiondMain(argc, argv);  
}  
  
cerr << "Unknown daemon name: " << daemon  
<< " (valid options: impalad, catalogd, statestored)" << endl;  
exit(1);  
}

4. 服务启动流程

sequenceDiagram
daemon-main.cc->>impalad-main.cc: ImpaladMain()
impalad-main.cc->>init.cc: InitCommonRuntime(argc,argv,init_jvm=true)
init.cc->>jni-util.cc: InitLibhdfs() <br/>通过调用hdfs方法创建fe jvm。
impalad-main.cc->>impala-server.cc:Start()
impala-server.cc->> exec-env.cc: StartStatestoreSubscriberService()<br/>订阅statestore数据同步
impala-server.cc->> exec-env.cc:StartKrpcService()<br/>启动集群内部节点RPC
impala-server.cc->> impala-server.cc: 启动服务监听

5. 请求处理流程

sequenceDiagram

cmd client ->> impala-server : ExecuteStatement()
impala-server ->> impala-server : ExecuteStatementCommon()
impala-server ->> impala-server : Execute()
impala-server ->> impala-server :ExecuteInternal()
impala-server ->> QueryDriver : RunFrontendPlanner()
QueryDriver ->> frontend.cc : GetExecRequest()
frontend.cc ->> JniFrontend: createExecRequest()
JniFrontend ->> Frontend.java : createExecRequest()<br/>fe部分生成查询计划
impala-server ->> ClientRequestState :set_result_metadata()设置结果头
impala-server ->> ClientRequestState : Exec()
ClientRequestState ->> ClientRequestState :ExecQueryOrDmlRequest()
ClientRequestState ->>AdmissionControlClient :SubmitForAdmission()
ClientRequestState ->> Coordinator : Exec()
impala-hs2-server ->> ClientRequestState : WaitAsync()等待结果返回
impala-hs2-server ->> impala-hs2-server : FetchInternal()
impala-hs2-server ->>  ClientRequestState: FetchRows()
ClientRequestState ->> ClientRequestState :FetchRowsInternal()
ClientRequestState ->> Coordinator :GetNext()
Coordinator ->> PlanRootSink:GetNext()
impala-hs2-server ->> impala-server : WaitForResults()
impala-server ->> ClientRequestState : BlockOnWait()等待结果

be请求处理堆栈信息如下, 在GetExecRequest中执行jni调用，就进入到fe进行执行计划生成。

Status Frontend::GetExecRequest(
    const TQueryCtx& query_ctx, TExecRequest* result) {
  return JniUtil::CallJniMethod(fe_, create_exec_request_id_, query_ctx, result);
}