版本号
Linux version 3.10.0-862.3.2.el7.x86_64 (gcc version 4.8.5 20150623 (Red Hat 4.8.5-28) (GCC) )
PostgreSQL 8.2.15 (Greenplum Database 4.3.99.00 build dev)
方法
原理
1. psql启动
2. master与segment通信
方法
- psql进入master
psql -d database -p 2345- 获取master上的后端进程号
ps -ef --forest | grep postgres- gdb联系master上的后端进程号
gdb
attach 34046
b cdbdisp_dispatchPlan
c- psql查询
SELECT * from test order by id;- 获取segment上的后端进程号
ps -ef --forest | grep postgres- gdb联系segment上的后端进程号
gdb
attach 35905
b exec_mpp_query
c- 在master的gdb上
c接下来就可以对segment进行代码跟踪调式了
原理(代码并非完全复制，请自行参照源码)
1. psql启动
函数PostmasterMain
/*
* Postmaster main entry point
*/
int
PostmasterMain(int argc, char *argv[])
{
// ListenAddresses是postgresql.conf配置的参数listen_addresses
if (ListenAddresses)
{
char *rawstring;
List *elemlist;
ListCell *l;
int success = 0;
/* Need a modifiable copy of ListenAddresses */
rawstring = pstrdup(ListenAddresses);
/* Parse string into list of identifiers */
if (!SplitIdentifierString(rawstring, ',', &elemlist))
{
/* syntax error in list */
ereport(FATAL,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("invalid list syntax for \"listen_addresses\"")));
}
foreach(l, elemlist)
{
char *curhost = (char *) lfirst(l);
// StreamServerPort创建和绑定socket,并进行监听
if (strcmp(curhost, "*") == 0)
status = StreamServerPort(AF_UNSPEC, NULL,
(unsigned short) PostPortNumber,
UnixSocketDir,
ListenSocket, MAXLISTEN);
else
status = StreamServerPort(AF_UNSPEC, curhost,
(unsigned short) PostPortNumber,
UnixSocketDir,
ListenSocket, MAXLISTEN);
if (status == STATUS_OK)
success++;
else
ereport(WARNING,
(errmsg("could not create listen socket for \"%s\"",
curhost)));
}
}
// 利用函数ServerLoop和全局静态变量ListenSocket进行循环接受连接请求
status = ServerLoop();
}函数StreamServerPort
/*
* StreamServerPort -- open a "listening" port to accept connections.
*
* Successfully opened sockets are added to the ListenSocket[] array,
* at the first position that isn't PGINVALID_SOCKET.
*
* RETURNS: STATUS_OK or STATUS_ERROR
*/
int
StreamServerPort(int family, char *hostName, unsigned short portNumber,
char *unixSocketName,
pgsocket ListenSocket[], int MaxListen)
{
for (addr = addrs; addr; addr = addr->ai_next)
{
// 创建socket
if ((fd = socket(addr->ai_family, SOCK_STREAM, 0)) < 0)
{
ereport(LOG,
(errcode_for_socket_access(),
/* translator: %s is IPv4, IPv6, or Unix */
errmsg("could not create %s socket: %m",
familyDesc)));
continue;
}
// 绑定socket
err = bind(fd, addr->ai_addr, addr->ai_addrlen);
// 监听
err = listen(fd, maxconn);
}
}函数ServerLoop
/*
* Main idle loop of postmaster
*/
static int
ServerLoop(void)
{
for (;;)
{
int selres;
if (acceptNewConnections)
{
// select进行I/O监视，有新的连接请求返回大于0，
selres = select(nSockets, &rmask, NULL, NULL, &timeout);
}
/*
* New connection pending on any of our sockets? If so, fork a child
* process to deal with it.
*/
if (selres > 0)
{
int i;
for (i = 0; i < MAXLISTEN; i++)
{
if (ListenSocket[i] == -1)
break;
if (FD_ISSET(ListenSocket[i], &rmask))
{
Port *port;
// ConnCreate->StreamConnection->accept，接受连接
port = ConnCreate(ListenSocket[i]);
if (port)
{
// 启动后端
BackendStartup(port);
/*
* We no longer need the open socket or port structure
* in this process
*/
StreamClose(port->sock);
ConnFree(port);
}
}
}
}
}
}函数BackendStartup
/*
* BackendStartup -- start backend process
*
* returns: STATUS_ERROR if the fork failed, STATUS_OK otherwise.
*
* Note: if you change this code, also consider StartAutovacuumWorker.
*/
static int
BackendStartup(Port *port)
{
pid = fork_process();
if (pid == 0) /* child */
{ // fork新的进程与psql进行交互
/* Close the postmaster's sockets */
ClosePostmasterPorts(false);
/* And run the backend */
proc_exit(BackendRun(port));
}
}函数BackendRun
/*
* BackendRun -- set up the backend's argument list and invoke PostgresMain()
*
* returns:
* Shouldn't return at all.
* If PostgresMain() fails, return status.
*/
static int
BackendRun(Port *port)
{
return PostgresMain(ac, av, port->database_name, port->user_name);
}函数PostgresMain
/* ----------------------------------------------------------------
* PostgresMain
* postgres main loop -- all backends, interactive or otherwise start here
*
* argc/argv are the command line arguments to be used. (When being forked
* by the postmaster, these are not the original argv array of the process.)
* username is the (possibly authenticated) PostgreSQL user name to be used
* for the session.
* ----------------------------------------------------------------
*/
int
PostgresMain(int argc, char *argv[],
const char *dbname, const char *username)
{
/*
* Non-error queries loop here.
*/
for (;;)
{
if (send_ready_for_query)
{
/*
* 1. ReadyForQuery->pq_endmessage->pq_putmessage->internal_putbytes,
* internal_putbytes把准备完毕的信息存放在全局静态变量PqSendBufferSize中
* 2. ReadyForQuery->pq_flush->internal_flush->secure_write->send，
* send通知psql后端准备完毕，至此psql启动完毕
*/
if (Gp_role == GP_ROLE_EXECUTE && Gp_is_writer)
{
ReadyForQuery_QEWriter(whereToSendOutput);
}
else
ReadyForQuery(whereToSendOutput);
send_ready_for_query = false;
}
/*
* 此处接受psql查询
* ReadCommand->SocketBackend->pq_getbyte->pq_recvbuf->secure_read->recv,
* recv获取psql发送的信息(包括信息类型，长度，sql)，
* 并且SocketBackend调用pq_getmessage将sql存放到input_message中。
* ReadCommand返回消息类型
*/
firstchar = ReadCommand(&input_message);
}
}2. master与segment通信
函数ExecutorStart
调用关系: exec_simple_query->PortalStart->ExecutorStart
void
ExecutorStart(QueryDesc *queryDesc, int eflags)
{
START_MEMORY_ACCOUNT(plannedStmt->memoryAccount);
{
/* If the interconnect has been set up; we need to catch any
* errors to shut it down -- so we have to wrap InitPlan in a PG_TRY() block. */
PG_TRY();
{
// InitPlan->ExecInitNode->ExecInitMotion
InitPlan(queryDesc, eflags);
if (Gp_role == GP_ROLE_DISPATCH &&
queryDesc->plannedstmt->planTree->dispatch == DISPATCH_PARALLEL)
{
/* Assign gang descriptions to the root slices of the slice forest. */
// 非常简单的select语句，这里并未做任何改变
InitRootSlices(queryDesc);
if (!(eflags & EXEC_FLAG_EXPLAIN_ONLY))
{
// AssignGangs->allocateWriterGang(primaryWriterGang==NULL)->createGang
AssignGangs(queryDesc, gp_singleton_segindex);
}
}
if (shouldDispatch)
{
// cdbdisp_dispatchPlan->cdbdisp_dispatchX->cdbdisp_dispatchToGang
cdbdisp_dispatchPlan(queryDesc, needDtxTwoPhase, true, estate->dispatcherState);
}
}
}
}函数ExecInitMotion
MotionState *
ExecInitMotion(Motion * node, EState *estate, int eflags)
{
MotionState *motionstate = NULL;
TupleDesc tupDesc;
Slice *sendSlice = NULL;
Slice *recvSlice = NULL;
SliceTable *sliceTable = estate->es_sliceTable;
int parentSliceIndex = estate->currentSliceIdInPlan;
/* Look up the sending gang's slice table entry. */
sendSlice = (Slice *)list_nth(sliceTable->slices, node->motionID);
/* QD must fill in the global slice table. */
if (Gp_role == GP_ROLE_DISPATCH)
{ // 主要作用是将sendSlice置为recvSlice的child，并且设置sendSlice
/* Look up the receiving (parent) gang's slice table entry. */
recvSlice = (Slice *)list_nth(sliceTable->slices, parentSliceIndex);
/* Sending slice become a children of recv slice */
recvSlice->children = lappend_int(recvSlice->children, sendSlice->sliceIndex);
sendSlice->parentIndex = parentSliceIndex;
sendSlice->rootIndex = recvSlice->rootIndex;
/* The gang beneath a Motion will be a reader. */
sendSlice->gangType = GANGTYPE_PRIMARY_READER;
}
}函数createGang
/*
* creates a new gang by logging on a session to each segDB involved
*
*/
static Gang *
createGang(GangType type, int gang_id, int size, int content, char *portal_name)
{
for (i = 0; i < threadCount; i++)
{
/*
* thread_DoConnect->cdbconn_doConnect->PQconnectdbParams连接segment数据库，
* 类似于psql连接postgres数据库
*/
pthread_err = gp_pthread_create(&pParms->thread, thread_DoConnect, pParms, "createGang");
}
/*
* wait for all of the DoConnect threads to complete.
*/
for (i = 0; i < threadCount; i++)
{
DoConnectParms *pParms = &doConnectParmsAr[i];
if (0 != pthread_join(pParms->thread, NULL))
{
elog(FATAL, "could not create segworker group");
}
}
}函数cdbdisp_dispatchToGang
void
cdbdisp_dispatchToGang(struct CdbDispatcherState *ds,
GpDispatchCommandType mppDispatchCommandType,
void *commandTypeParms,
struct Gang *gp,
int sliceIndex,
unsigned int maxSlices,
CdbDispatchDirectDesc *disp_direct)
{
/*
* Create the threads. (which also starts the dispatching).
*/
for (i = 0; i < newThreads; i++)
{
DispatchCommandParms *pParms = &(ds->dispatchThreads->dispatchCommandParmsAr + ds->dispatchThreads->threadCount)[i];
if (gp_connections_per_thread==0)
{
Assert(newThreads <= 1);
thread_DispatchOut(pParms);
}
else
{
int pthread_err = 0;
pParms->thread_valid = true;
/*
* thread_DispatchCommand->thread_DispatchOut->dispatchCommandQuery->PQsendGpQuery_shared，
* 类似于psql发送查询信息
*/
pthread_err = gp_pthread_create(&pParms->thread, thread_DispatchCommand, pParms, "dispatchToGang");
}
}
}