PostgreSQL 原始碼解讀（13）- 插入資料#12（PostgresMain）
本文簡單介紹了PG插入資料部分的原始碼，主要內容包括PostgresMain函式的實現邏輯，該函式位於postgres.c檔案中。
一、原始碼解讀
PostgresMain函式
/* ----------------------------------------------------------------
* 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.)
* dbname is the name of the database to connect to, or NULL if the database
* name should be extracted from the command line arguments or defaulted.
* username is the PostgreSQL user name to be used for the session.
* ----------------------------------------------------------------
*/
/*
輸入：
argc/argv-Main函式的輸入引數
dbname-資料庫名稱
username-使用者名稱
輸出：
無
*/
void
PostgresMain(int argc, char *argv[],
const char *dbname,
const char *username)
{
int firstchar;//臨時變數，讀取輸入的Command
StringInfoData input_message;//字串增強結構體
sigjmp_buf local_sigjmp_buf;//系統變數
volatile bool send_ready_for_query = true;//
bool disable_idle_in_transaction_timeout = false;
/* Initialize startup process environment if necessary. */
if (!IsUnderPostmaster//未初始化？initialized for the bootstrap/standalone case
InitStandaloneProcess(argv[0]);//初始化程式
SetProcessingMode(InitProcessing);//設定程式狀態為InitProcessing
/*
* Set default values for command-line options.
*/
if (!IsUnderPostmaster)
InitializeGUCOptions();//初始化GUC引數，GUC=Grand Unified Configuration
/*
* Parse command-line options.
*/
process_postgres_switches(argc, argv, PGC_POSTMASTER, &dbname);//解析輸入引數
/* Must have gotten a database name, or have a default (the username) */
if (dbname == NULL)//輸入的dbname為空
{
dbname = username;//設定為使用者名稱
if (dbname == NULL)//如仍為空，報錯
ereport(FATAL,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("%s: no database nor user name specified",
progname)));
}
/* Acquire configuration parameters, unless inherited from postmaster */
if (!IsUnderPostmaster)
{
if (!SelectConfigFiles(userDoption, progname))//讀取配置檔案conf/hba檔案&定位資料目錄
proc_exit(1);
}
/*
* Set up signal handlers and masks.
*
* Note that postmaster blocked all signals before forking child process,
* so there is no race condition whereby we might receive a signal before
* we have set up the handler.
*
* Also note: it's best not to use any signals that are SIG_IGNored in the
* postmaster. If such a signal arrives before we are able to change the
* handler to non-SIG_IGN, it'll get dropped. Instead, make a dummy
* handler in the postmaster to reserve the signal. (Of course, this isn't
* an issue for signals that are locally generated, such as SIGALRM and
* SIGPIPE.)
*/
if (am_walsender)//wal sender程式？
WalSndSignals();//如果是，則呼叫WalSndSignals
else//不是wal sender程式
{
pqsignal(SIGHUP, PostgresSigHupHandler); /* set flag to read config
* file */
pqsignal(SIGINT, StatementCancelHandler); /* cancel current query */
pqsignal(SIGTERM, die); /* cancel current query and exit */
/*
* In a standalone backend, SIGQUIT can be generated from the keyboard
* easily, while SIGTERM cannot, so we make both signals do die()
* rather than quickdie().
*/
if (IsUnderPostmaster)
pqsignal(SIGQUIT, quickdie); /* hard crash time */
else
pqsignal(SIGQUIT, die); /* cancel current query and exit */
InitializeTimeouts(); /* establishes SIGALRM handler */
/*
* Ignore failure to write to frontend. Note: if frontend closes
* connection, we will notice it and exit cleanly when control next
* returns to outer loop. This seems safer than forcing exit in the
* midst of output during who-knows-what operation...
*/
pqsignal(SIGPIPE, SIG_IGN);
pqsignal(SIGUSR1, procsignal_sigusr1_handler);
pqsignal(SIGUSR2, SIG_IGN);
pqsignal(SIGFPE, FloatExceptionHandler);
/*
* Reset some signals that are accepted by postmaster but not by
* backend
*/
pqsignal(SIGCHLD, SIG_DFL); /* system() requires this on some
* platforms */
}
pqinitmask();//Initialize BlockSig, UnBlockSig, and StartupBlockSig.
if (IsUnderPostmaster)
{
/* We allow SIGQUIT (quickdie) at all times */
sigdelset(&BlockSig, SIGQUIT);
}
PG_SETMASK(&BlockSig); /* block everything except SIGQUIT */
if (!IsUnderPostmaster)
{
/*
* Validate we have been given a reasonable-looking DataDir (if under
* postmaster, assume postmaster did this already).
*/
checkDataDir();//確認資料庫路徑OK，使用stat命令
/* Change into DataDir (if under postmaster, was done already) */
ChangeToDataDir();//切換至資料庫路徑，使用chdir命令
/*
* Create lockfile for data directory.
*/
CreateDataDirLockFile(false);//建立鎖定檔案，CreateLockFile(DIRECTORY_LOCK_FILE, amPostmaster, "", true, DataDir);
/* read control file (error checking and contains config ) */
LocalProcessControlFile(false);//Read the control file, set respective GUCs.
/* Initialize MaxBackends (if under postmaster, was done already) */
InitializeMaxBackends();//Initialize MaxBackends value from config options.
}
/* Early initialization */
BaseInit();//基礎的初始化
/*
* Create a per-backend PGPROC struct in shared memory, except in the
* EXEC_BACKEND case where this was done in SubPostmasterMain. We must do
* this before we can use LWLocks (and in the EXEC_BACKEND case we already
* had to do some stuff with LWLocks).
*/
// initialize a per-process data structure for this backend
#ifdef EXEC_BACKEND
if (!IsUnderPostmaster)
InitProcess();
#else
InitProcess();
#endif
/* We need to allow SIGINT, etc during the initial transaction */
PG_SETMASK(&UnBlockSig);
/*
* General initialization.
*
* NOTE: if you are tempted to add code in this vicinity, consider putting
* it inside InitPostgres() instead. In particular, anything that
* involves database access should be there, not here.
*/
InitPostgres(dbname, InvalidOid, username, InvalidOid, NULL, false);//Initialize POSTGRES
/*
* If the PostmasterContext is still around, recycle the space; we don't
* need it anymore after InitPostgres completes. Note this does not trash
* *MyProcPort, because ConnCreate() allocated that space with malloc()
* ... else we'd need to copy the Port data first. Also, subsidiary data
* such as the username isn't lost either; see ProcessStartupPacket().
*/
if (PostmasterContext)
{
MemoryContextDelete(PostmasterContext);
PostmasterContext = NULL;
}
SetProcessingMode(NormalProcessing);//完成初始化後，設定程式模式為NormalProcessing
/*
* Now all GUC states are fully set up. Report them to client if
* appropriate.
*/
BeginReportingGUCOptions();//Report GUC
/*
* Also set up handler to log session end; we have to wait till now to be
* sure Log_disconnections has its final value.
*/
if (IsUnderPostmaster && Log_disconnections)
on_proc_exit(log_disconnections, 0);//this function adds a callback function to the list of functions invoked by proc_exit()
/* Perform initialization specific to a WAL sender process. */
if (am_walsender)
InitWalSender();//初始化 WAL sender process
/*
* process any libraries that should be preloaded at backend start (this
* likewise can't be done until GUC settings are complete)
*/
process_session_preload_libraries();//載入LIB
/*
* Send this backend's cancellation info to the frontend.
*/
if (whereToSendOutput == DestRemote)
{
StringInfoData buf;
pq_beginmessage(&buf, 'K');
pq_sendint32(&buf, (int32) MyProcPid);
pq_sendint32(&buf, (int32) MyCancelKey);
pq_endmessage(&buf);
/* Need not flush since ReadyForQuery will do it. */
}
/* Welcome banner for standalone case */
if (whereToSendOutput == DestDebug)
printf("\nPostgreSQL stand-alone backend %s\n", PG_VERSION);
/*
* Create the memory context we will use in the main loop.
*
* MessageContext is reset once per iteration of the main loop, ie, upon
* completion of processing of each command message from the client.
*/
//初始化記憶體上下文：MessageContext
MessageContext = AllocSetContextCreate(TopMemoryContext,
"MessageContext",
ALLOCSET_DEFAULT_SIZES);
/*
* Create memory context and buffer used for RowDescription messages. As
* SendRowDescriptionMessage(), via exec_describe_statement_message(), is
* frequently executed for ever single statement, we don't want to
* allocate a separate buffer every time.
*/
//TODO 傳輸RowDescription messages？
row_description_context = AllocSetContextCreate(TopMemoryContext,
"RowDescriptionContext",
ALLOCSET_DEFAULT_SIZES);
MemoryContextSwitchTo(row_description_context);
initStringInfo(&row_description_buf);
MemoryContextSwitchTo(TopMemoryContext);
/*
* Remember stand-alone backend startup time
*/
if (!IsUnderPostmaster)
PgStartTime = GetCurrentTimestamp();//記錄啟動時間
/*
* POSTGRES main processing loop begins here
*
* If an exception is encountered, processing resumes here so we abort the
* current transaction and start a new one.
*
* You might wonder why this isn't coded as an infinite loop around a
* PG_TRY construct. The reason is that this is the bottom of the
* exception stack, and so with PG_TRY there would be no exception handler
* in force at all during the CATCH part. By leaving the outermost setjmp
* always active, we have at least some chance of recovering from an error
* during error recovery. (If we get into an infinite loop thereby, it
* will soon be stopped by overflow of elog.c's internal state stack.)
*
* Note that we use sigsetjmp(..., 1), so that this function's signal mask
* (to wit, UnBlockSig) will be restored when longjmp'ing to here. This
* is essential in case we longjmp'd out of a signal handler on a platform
* where that leaves the signal blocked. It's not redundant with the
* unblock in AbortTransaction() because the latter is only called if we
* were inside a transaction.
*/
if (sigsetjmp(local_sigjmp_buf, 1) != 0)//
{
/*
* NOTE: if you are tempted to add more code in this if-block,
* consider the high probability that it should be in
* AbortTransaction() instead. The only stuff done directly here
* should be stuff that is guaranteed to apply *only* for outer-level
* error recovery, such as adjusting the FE/BE protocol status.
*/
/* Since not using PG_TRY, must reset error stack by hand */
error_context_stack = NULL;
/* Prevent interrupts while cleaning up */
HOLD_INTERRUPTS();
/*
* Forget any pending QueryCancel request, since we're returning to
* the idle loop anyway, and cancel any active timeout requests. (In
* future we might want to allow some timeout requests to survive, but
* at minimum it'd be necessary to do reschedule_timeouts(), in case
* we got here because of a query cancel interrupting the SIGALRM
* interrupt handler.) Note in particular that we must clear the
* statement and lock timeout indicators, to prevent any future plain
* query cancels from being misreported as timeouts in case we're
* forgetting a timeout cancel.
*/
disable_all_timeouts(false);
QueryCancelPending = false; /* second to avoid race condition */
stmt_timeout_active = false;
/* Not reading from the client anymore. */
DoingCommandRead = false;
/* Make sure libpq is in a good state */
pq_comm_reset();
/* Report the error to the client and/or server log */
EmitErrorReport();
/*
* Make sure debug_query_string gets reset before we possibly clobber
* the storage it points at.
*/
debug_query_string = NULL;
/*
* Abort the current transaction in order to recover.
*/
AbortCurrentTransaction();
if (am_walsender)
WalSndErrorCleanup();
PortalErrorCleanup();
SPICleanup();
/*
* We can't release replication slots inside AbortTransaction() as we
* need to be able to start and abort transactions while having a slot
* acquired. But we never need to hold them across top level errors,
* so releasing here is fine. There's another cleanup in ProcKill()
* ensuring we'll correctly cleanup on FATAL errors as well.
*/
if (MyReplicationSlot != NULL)
ReplicationSlotRelease();
/* We also want to cleanup temporary slots on error. */
ReplicationSlotCleanup();
jit_reset_after_error();
/*
* Now return to normal top-level context and clear ErrorContext for
* next time.
*/
MemoryContextSwitchTo(TopMemoryContext);
FlushErrorState();
/*
* If we were handling an extended-query-protocol message, initiate
* skip till next Sync. This also causes us not to issue
* ReadyForQuery (until we get Sync).
*/
if (doing_extended_query_message)
ignore_till_sync = true;
/* We don't have a transaction command open anymore */
xact_started = false;
/*
* If an error occurred while we were reading a message from the
* client, we have potentially lost track of where the previous
* message ends and the next one begins. Even though we have
* otherwise recovered from the error, we cannot safely read any more
* messages from the client, so there isn't much we can do with the
* connection anymore.
*/
if (pq_is_reading_msg())
ereport(FATAL,
(errcode(ERRCODE_PROTOCOL_VIOLATION),
errmsg("terminating connection because protocol synchronization was lost")));
/* Now we can allow interrupts again */
RESUME_INTERRUPTS();
}
/* We can now handle ereport(ERROR) */
PG_exception_stack = &local_sigjmp_buf;
if (!ignore_till_sync)
send_ready_for_query = true; /* initially, or after error */
/*
* Non-error queries loop here.
*/
for (;;)//主迴圈
{
/*
* At top of loop, reset extended-query-message flag, so that any
* errors encountered in "idle" state don't provoke skip.
*/
doing_extended_query_message = false;
/*
* Release storage left over from prior query cycle, and create a new
* query input buffer in the cleared MessageContext.
*/
MemoryContextSwitchTo(MessageContext);//切換至MessageContext
MemoryContextResetAndDeleteChildren(MessageContext);
initStringInfo(&input_message);//初始化輸入的資訊
/*
* Also consider releasing our catalog snapshot if any, so that it's
* not preventing advance of global xmin while we wait for the client.
*/
InvalidateCatalogSnapshotConditionally();
/*
* (1) If we've reached idle state, tell the frontend we're ready for
* a new query.
*
* Note: this includes fflush()'ing the last of the prior output.
*
* This is also a good time to send collected statistics to the
* collector, and to update the PS stats display. We avoid doing
* those every time through the message loop because it'd slow down
* processing of batched messages, and because we don't want to report
* uncommitted updates (that confuses autovacuum). The notification
* processor wants a call too, if we are not in a transaction block.
*/
if (send_ready_for_query)//I am ready!
{
if (IsAbortedTransactionBlockState())
{
set_ps_display("idle in transaction (aborted)", false);
pgstat_report_activity(STATE_IDLEINTRANSACTION_ABORTED, NULL);
/* Start the idle-in-transaction timer */
if (IdleInTransactionSessionTimeout > 0)
{
disable_idle_in_transaction_timeout = true;
enable_timeout_after(IDLE_IN_TRANSACTION_SESSION_TIMEOUT,
IdleInTransactionSessionTimeout);
}
}
else if (IsTransactionOrTransactionBlock())
{
set_ps_display("idle in transaction", false);
pgstat_report_activity(STATE_IDLEINTRANSACTION, NULL);
/* Start the idle-in-transaction timer */
if (IdleInTransactionSessionTimeout > 0)
{
disable_idle_in_transaction_timeout = true;
enable_timeout_after(IDLE_IN_TRANSACTION_SESSION_TIMEOUT,
IdleInTransactionSessionTimeout);
}
}
else
{
ProcessCompletedNotifies();
pgstat_report_stat(false);
set_ps_display("idle", false);
pgstat_report_activity(STATE_IDLE, NULL);
}
ReadyForQuery(whereToSendOutput);
send_ready_for_query = false;
}
/*
* (2) Allow asynchronous signals to be executed immediately if they
* come in while we are waiting for client input. (This must be
* conditional since we don't want, say, reads on behalf of COPY FROM
* STDIN doing the same thing.)
*/
DoingCommandRead = true;
/*
* (3) read a command (loop blocks here)
*/
firstchar = ReadCommand(&input_message);//讀取命令
/*
* (4) disable async signal conditions again.
*
* Query cancel is supposed to be a no-op when there is no query in
* progress, so if a query cancel arrived while we were idle, just
* reset QueryCancelPending. ProcessInterrupts() has that effect when
* it's called when DoingCommandRead is set, so check for interrupts
* before resetting DoingCommandRead.
*/
CHECK_FOR_INTERRUPTS();
DoingCommandRead = false;
/*
* (5) turn off the idle-in-transaction timeout
*/
if (disable_idle_in_transaction_timeout)
{
disable_timeout(IDLE_IN_TRANSACTION_SESSION_TIMEOUT, false);
disable_idle_in_transaction_timeout = false;
}
/*
* (6) check for any other interesting events that happened while we
* slept.
*/
if (ConfigReloadPending)
{
ConfigReloadPending = false;
ProcessConfigFile(PGC_SIGHUP);
}
/*
* (7) process the command. But ignore it if we're skipping till
* Sync.
*/
if (ignore_till_sync && firstchar != EOF)
continue;
switch (firstchar)
{
case 'Q': /* simple query */
{
const char *query_string;
/* Set statement_timestamp() */
SetCurrentStatementStartTimestamp();
query_string = pq_getmsgstring(&input_message);//SQL語句
pq_getmsgend(&input_message);
if (am_walsender)
{
if (!exec_replication_command(query_string))
exec_simple_query(query_string);
}
else
exec_simple_query(query_string);//執行SQL語句
send_ready_for_query = true;
}
break;
case 'P': /* parse */
{
const char *stmt_name;
const char *query_string;
int numParams;
Oid *paramTypes = NULL;
forbidden_in_wal_sender(firstchar);
/* Set statement_timestamp() */
SetCurrentStatementStartTimestamp();
stmt_name = pq_getmsgstring(&input_message);
query_string = pq_getmsgstring(&input_message);
numParams = pq_getmsgint(&input_message, 2);
if (numParams > 0)
{
int i;
paramTypes = (Oid *) palloc(numParams * sizeof(Oid));
for (i = 0; i < numParams; i++)
paramTypes[i] = pq_getmsgint(&input_message, 4);
}
pq_getmsgend(&input_message);
exec_parse_message(query_string, stmt_name,
paramTypes, numParams);
}
break;
case 'B': /* bind */
forbidden_in_wal_sender(firstchar);
/* Set statement_timestamp() */
SetCurrentStatementStartTimestamp();
/*
* this message is complex enough that it seems best to put
* the field extraction out-of-line
*/
exec_bind_message(&input_message);
break;
case 'E': /* execute */
{
const char *portal_name;
int max_rows;
forbidden_in_wal_sender(firstchar);
/* Set statement_timestamp() */
SetCurrentStatementStartTimestamp();
portal_name = pq_getmsgstring(&input_message);
max_rows = pq_getmsgint(&input_message, 4);
pq_getmsgend(&input_message);
exec_execute_message(portal_name, max_rows);
}
break;
case 'F': /* fastpath function call */
forbidden_in_wal_sender(firstchar);
/* Set statement_timestamp() */
SetCurrentStatementStartTimestamp();
/* Report query to various monitoring facilities. */
pgstat_report_activity(STATE_FASTPATH, NULL);
set_ps_display("<FASTPATH>", false);
/* start an xact for this function invocation */
start_xact_command();
/*
* Note: we may at this point be inside an aborted
* transaction. We can't throw error for that until we've
* finished reading the function-call message, so
* HandleFunctionRequest() must check for it after doing so.
* Be careful not to do anything that assumes we're inside a
* valid transaction here.
*/
/* switch back to message context */
MemoryContextSwitchTo(MessageContext);
HandleFunctionRequest(&input_message);
/* commit the function-invocation transaction */
finish_xact_command();
send_ready_for_query = true;
break;
case 'C': /* close */
{
int close_type;
const char *close_target;
forbidden_in_wal_sender(firstchar);
close_type = pq_getmsgbyte(&input_message);
close_target = pq_getmsgstring(&input_message);
pq_getmsgend(&input_message);
switch (close_type)
{
case 'S':
if (close_target[0] != '\0')
DropPreparedStatement(close_target, false);
else
{
/* special-case the unnamed statement */
drop_unnamed_stmt();
}
break;
case 'P':
{
Portal portal;
portal = GetPortalByName(close_target);
if (PortalIsValid(portal))
PortalDrop(portal, false);
}
break;
default:
ereport(ERROR,
(errcode(ERRCODE_PROTOCOL_VIOLATION),
errmsg("invalid CLOSE message subtype %d",
close_type)));
break;
}
if (whereToSendOutput == DestRemote)
pq_putemptymessage('3'); /* CloseComplete */
}
break;
case 'D': /* describe */
{
int describe_type;
const char *describe_target;
forbidden_in_wal_sender(firstchar);
/* Set statement_timestamp() (needed for xact) */
SetCurrentStatementStartTimestamp();
describe_type = pq_getmsgbyte(&input_message);
describe_target = pq_getmsgstring(&input_message);
pq_getmsgend(&input_message);
switch (describe_type)
{
case 'S':
exec_describe_statement_message(describe_target);
break;
case 'P':
exec_describe_portal_message(describe_target);
break;
default:
ereport(ERROR,
(errcode(ERRCODE_PROTOCOL_VIOLATION),
errmsg("invalid DESCRIBE message subtype %d",
describe_type)));
break;
}
}
break;
case 'H': /* flush */
pq_getmsgend(&input_message);
if (whereToSendOutput == DestRemote)
pq_flush();
break;
case 'S': /* sync */
pq_getmsgend(&input_message);
finish_xact_command();
send_ready_for_query = true;
break;
/*
* 'X' means that the frontend is closing down the socket. EOF
* means unexpected loss of frontend connection. Either way,
* perform normal shutdown.
*/
case 'X':
case EOF:
/*
* Reset whereToSendOutput to prevent ereport from attempting
* to send any more messages to client.
*/
if (whereToSendOutput == DestRemote)
whereToSendOutput = DestNone;
/*
* NOTE: if you are tempted to add more code here, DON'T!
* Whatever you had in mind to do should be set up as an
* on_proc_exit or on_shmem_exit callback, instead. Otherwise
* it will fail to be called during other backend-shutdown
* scenarios.
*/
proc_exit(0);
case 'd': /* copy data */
case 'c': /* copy done */
case 'f': /* copy fail */
/*
* Accept but ignore these messages, per protocol spec; we
* probably got here because a COPY failed, and the frontend
* is still sending data.
*/
break;
default:
ereport(FATAL,
(errcode(ERRCODE_PROTOCOL_VIOLATION),
errmsg("invalid frontend message type %d",
firstchar)));
}
} /* end of input-reading loop */
}
二、基礎資訊
PostgresMain函式使用的資料結構、宏定義以及依賴的函式等。
資料結構/宏定義
1、StringInfoData
/*-------------------------
* StringInfoData holds information about an extensible string.
* data is the current buffer for the string (allocated with palloc).
* len is the current string length. There is guaranteed to be
* a terminating '\0' at data[len], although this is not very
* useful when the string holds binary data rather than text.
* maxlen is the allocated size in bytes of 'data', i.e. the maximum
* string size (including the terminating '\0' char) that we can
* currently store in 'data' without having to reallocate
* more space. We must always have maxlen > len.
* cursor is initialized to zero by makeStringInfo or initStringInfo,
* but is not otherwise touched by the stringinfo.c routines.
* Some routines use it to scan through a StringInfo.
*-------------------------
*/
typedef struct StringInfoData
{
char *data;
int len;
int maxlen;
int cursor;
} StringInfoData;
typedef StringInfoData *StringInfo;
2、宏定義
#ifndef WIN32
#define PG_SETMASK(mask) sigprocmask(SIG_SETMASK, mask, NULL)
#else
/* Emulate POSIX sigset_t APIs on Windows */
typedef int sigset_t;
extern int pqsigsetmask(int mask);
#define PG_SETMASK(mask) pqsigsetmask(*(mask))
#define sigemptyset(set) (*(set) = 0)
#define sigfillset(set) (*(set) = ~0)
#define sigaddset(set, signum) (*(set) |= (sigmask(signum)))
#define sigdelset(set, signum) (*(set) &= ~(sigmask(signum)))
#endif /* WIN32 */
3、全域性變數
/*
* IsPostmasterEnvironment is true in a postmaster process and any postmaster
* child process; it is false in a standalone process (bootstrap or
* standalone backend). IsUnderPostmaster is true in postmaster child
* processes. Note that "child process" includes all children, not only
* regular backends. These should be set correctly as early as possible
* in the execution of a process, so that error handling will do the right
* things if an error should occur during process initialization.
*
* These are initialized for the bootstrap/standalone case.
*/
bool IsPostmasterEnvironment = false;
bool IsUnderPostmaster = false;
bool IsBinaryUpgrade = false;
bool IsBackgroundWorker = false;
bool am_walsender = false; /* Am I a walsender process? */
依賴的函式
1、InitStandaloneProcess
/*
* Initialize the basic environment for a standalone process.
*
* argv0 has to be suitable to find the program's executable.
*/
void
InitStandaloneProcess(const char *argv0)
{
Assert(!IsPostmasterEnvironment);
MyProcPid = getpid(); /* reset MyProcPid */
MyStartTime = time(NULL); /* set our start time in case we call elog */
/* Initialize process-local latch support */
InitializeLatchSupport();
MyLatch = &LocalLatchData;
InitLatch(MyLatch);
/* Compute paths, no postmaster to inherit from */
if (my_exec_path[0] == '\0')
{
if (find_my_exec(argv0, my_exec_path) < 0)
elog(FATAL, "%s: could not locate my own executable path",
argv0);
}
if (pkglib_path[0] == '\0')
get_pkglib_path(my_exec_path, pkglib_path);
}
2、InitializeGUCOptions
/*
* Initialize GUC options during program startup.
*
* Note that we cannot read the config file yet, since we have not yet
* processed command-line switches.
*/
void
InitializeGUCOptions(void)
{
int i;
/*
* Before log_line_prefix could possibly receive a nonempty setting, make
* sure that timezone processing is minimally alive (see elog.c).
*/
pg_timezone_initialize();
/*
* Build sorted array of all GUC variables.
*/
build_guc_variables();
/*
* Load all variables with their compiled-in defaults, and initialize
* status fields as needed.
*/
for (i = 0; i < num_guc_variables; i++)
{
InitializeOneGUCOption(guc_variables[i]);
}
guc_dirty = false;
reporting_enabled = false;
/*
* Prevent any attempt to override the transaction modes from
* non-interactive sources.
*/
SetConfigOption("transaction_isolation", "default",
PGC_POSTMASTER, PGC_S_OVERRIDE);
SetConfigOption("transaction_read_only", "no",
PGC_POSTMASTER, PGC_S_OVERRIDE);
SetConfigOption("transaction_deferrable", "no",
PGC_POSTMASTER, PGC_S_OVERRIDE);
/*
* For historical reasons, some GUC parameters can receive defaults from
* environment variables. Process those settings.
*/
InitializeGUCOptionsFromEnvironment();
}
3、process_postgres_switches
/* ----------------------------------------------------------------
* process_postgres_switches
* Parse command line arguments for PostgresMain
*
* This is called twice, once for the "secure" options coming from the
* postmaster or command line, and once for the "insecure" options coming
* from the client's startup packet. The latter have the same syntax but
* may be restricted in what they can do.
*
* argv[0] is ignored in either case (it's assumed to be the program name).
*
* ctx is PGC_POSTMASTER for secure options, PGC_BACKEND for insecure options
* coming from the client, or PGC_SU_BACKEND for insecure options coming from
* a superuser client.
*
* If a database name is present in the command line arguments, it's
* returned into *dbname (this is allowed only if *dbname is initially NULL).
* ----------------------------------------------------------------
*/
void
process_postgres_switches(int argc, char *argv[], GucContext ctx,
const char **dbname)
{
bool secure = (ctx == PGC_POSTMASTER);
int errs = 0;
GucSource gucsource;
int flag;
if (secure)
{
gucsource = PGC_S_ARGV; /* switches came from command line */
/* Ignore the initial --single argument, if present */
if (argc > 1 && strcmp(argv[1], "--single") == 0)
{
argv++;
argc--;
}
}
else
{
gucsource = PGC_S_CLIENT; /* switches came from client */
}
#ifdef HAVE_INT_OPTERR
/*
* Turn this off because it's either printed to stderr and not the log
* where we'd want it, or argv[0] is now "--single", which would make for
* a weird error message. We print our own error message below.
*/
opterr = 0;
#endif
/*
* Parse command-line options. CAUTION: keep this in sync with
* postmaster/postmaster.c (the option sets should not conflict) and with
* the common help() function in main/main.c.
*/
while ((flag = getopt(argc, argv, "B:bc:C:D:d:EeFf:h:ijk:lN:nOo:Pp:r:S:sTt:v:W:-:")) != -1)
{
switch (flag)
{
case 'B':
SetConfigOption("shared_buffers", optarg, ctx, gucsource);
break;
case 'b':
/* Undocumented flag used for binary upgrades */
if (secure)
IsBinaryUpgrade = true;
break;
case 'C':
/* ignored for consistency with the postmaster */
break;
case 'D':
if (secure)
userDoption = strdup(optarg);
break;
case 'd':
set_debug_options(atoi(optarg), ctx, gucsource);
break;
case 'E':
if (secure)
EchoQuery = true;
break;
case 'e':
SetConfigOption("datestyle", "euro", ctx, gucsource);
break;
case 'F':
SetConfigOption("fsync", "false", ctx, gucsource);
break;
case 'f':
if (!set_plan_disabling_options(optarg, ctx, gucsource))
errs++;
break;
case 'h':
SetConfigOption("listen_addresses", optarg, ctx, gucsource);
break;
case 'i':
SetConfigOption("listen_addresses", "*", ctx, gucsource);
break;
case 'j':
if (secure)
UseSemiNewlineNewline = true;
break;
case 'k':
SetConfigOption("unix_socket_directories", optarg, ctx, gucsource);
break;
case 'l':
SetConfigOption("ssl", "true", ctx, gucsource);
break;
case 'N':
SetConfigOption("max_connections", optarg, ctx, gucsource);
break;
case 'n':
/* ignored for consistency with postmaster */
break;
case 'O':
SetConfigOption("allow_system_table_mods", "true", ctx, gucsource);
break;
case 'o':
errs++;
break;
case 'P':
SetConfigOption("ignore_system_indexes", "true", ctx, gucsource);
break;
case 'p':
SetConfigOption("port", optarg, ctx, gucsource);
break;
case 'r':
/* send output (stdout and stderr) to the given file */
if (secure)
strlcpy(OutputFileName, optarg, MAXPGPATH);
break;
case 'S':
SetConfigOption("work_mem", optarg, ctx, gucsource);
break;
case 's':
SetConfigOption("log_statement_stats", "true", ctx, gucsource);
break;
case 'T':
/* ignored for consistency with the postmaster */
break;
case 't':
{
const char *tmp = get_stats_option_name(optarg);
if (tmp)
SetConfigOption(tmp, "true", ctx, gucsource);
else
errs++;
break;
}
case 'v':
/*
* -v is no longer used in normal operation, since
* FrontendProtocol is already set before we get here. We keep
* the switch only for possible use in standalone operation,
* in case we ever support using normal FE/BE protocol with a
* standalone backend.
*/
if (secure)
FrontendProtocol = (ProtocolVersion) atoi(optarg);
break;
case 'W':
SetConfigOption("post_auth_delay", optarg, ctx, gucsource);
break;
case 'c':
case '-':
{
char *name,
*value;
ParseLongOption(optarg, &name, &value);
if (!value)
{
if (flag == '-')
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
errmsg("--%s requires a value",
optarg)));
else
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
errmsg("-c %s requires a value",
optarg)));
}
SetConfigOption(name, value, ctx, gucsource);
free(name);
if (value)
free(value);
break;
}
default:
errs++;
break;
}
if (errs)
break;
}
/*
* Optional database name should be there only if *dbname is NULL.
*/
if (!errs && dbname && *dbname == NULL && argc - optind >= 1)
*dbname = strdup(argv[optind++]);
if (errs || argc != optind)
{
if (errs)
optind--; /* complain about the previous argument */
/* spell the error message a bit differently depending on context */
if (IsUnderPostmaster)
ereport(FATAL,
(errcode(ERRCODE_SYNTAX_ERROR),
errmsg("invalid command-line argument for server process: %s", argv[optind]),
errhint("Try \"%s --help\" for more information.", progname)));
else
ereport(FATAL,
(errcode(ERRCODE_SYNTAX_ERROR),
errmsg("%s: invalid command-line argument: %s",
progname, argv[optind]),
errhint("Try \"%s --help\" for more information.", progname)));
}
/*
* Reset getopt(3) library so that it will work correctly in subprocesses
* or when this function is called a second time with another array.
*/
optind = 1;
#ifdef HAVE_INT_OPTRESET
optreset = 1; /* some systems need this too */
#endif
}
4、SelectConfigFiles
/*
* Select the configuration files and data directory to be used, and
* do the initial read of postgresql.conf.
*
* This is called after processing command-line switches.
* userDoption is the -D switch value if any (NULL if unspecified).
* progname is just for use in error messages.
*
* Returns true on success; on failure, prints a suitable error message
* to stderr and returns false.
*/
bool
SelectConfigFiles(const char *userDoption, const char *progname)
{
char *configdir;
char *fname;
struct stat stat_buf;
/* configdir is -D option, or $PGDATA if no -D */
if (userDoption)
configdir = make_absolute_path(userDoption);
else
configdir = make_absolute_path(getenv("PGDATA"));
if (configdir && stat(configdir, &stat_buf) != 0)
{
write_stderr("%s: could not access directory \"%s\": %s\n",
progname,
configdir,
strerror(errno));
if (errno == ENOENT)
write_stderr("Run initdb or pg_basebackup to initialize a PostgreSQL data directory.\n");
return false;
}
/*
* Find the configuration file: if config_file was specified on the
* command line, use it, else use configdir/postgresql.conf. In any case
* ensure the result is an absolute path, so that it will be interpreted
* the same way by future backends.
*/
if (ConfigFileName)
fname = make_absolute_path(ConfigFileName);
else if (configdir)
{
fname = guc_malloc(FATAL,
strlen(configdir) + strlen(CONFIG_FILENAME) + 2);
sprintf(fname, "%s/%s", configdir, CONFIG_FILENAME);
}
else
{
write_stderr("%s does not know where to find the server configuration file.\n"
"You must specify the --config-file or -D invocation "
"option or set the PGDATA environment variable.\n",
progname);
return false;
}
/*
* Set the ConfigFileName GUC variable to its final value, ensuring that
* it can't be overridden later.
*/
SetConfigOption("config_file", fname, PGC_POSTMASTER, PGC_S_OVERRIDE);
free(fname);
/*
* Now read the config file for the first time.
*/
if (stat(ConfigFileName, &stat_buf) != 0)
{
write_stderr("%s: could not access the server configuration file \"%s\": %s\n",
progname, ConfigFileName, strerror(errno));
free(configdir);
return false;
}
/*
* Read the configuration file for the first time. This time only the
* data_directory parameter is picked up to determine the data directory,
* so that we can read the PG_AUTOCONF_FILENAME file next time.
*/
ProcessConfigFile(PGC_POSTMASTER);
/*
* If the data_directory GUC variable has been set, use that as DataDir;
* otherwise use configdir if set; else punt.
*
* Note: SetDataDir will copy and absolute-ize its argument, so we don't
* have to.
*/
if (data_directory)
SetDataDir(data_directory);
else if (configdir)
SetDataDir(configdir);
else
{
write_stderr("%s does not know where to find the database system data.\n"
"This can be specified as \"data_directory\" in \"%s\", "
"or by the -D invocation option, or by the "
"PGDATA environment variable.\n",
progname, ConfigFileName);
return false;
}
/*
* Reflect the final DataDir value back into the data_directory GUC var.
* (If you are wondering why we don't just make them a single variable,
* it's because the EXEC_BACKEND case needs DataDir to be transmitted to
* child backends specially. XXX is that still true? Given that we now
* chdir to DataDir, EXEC_BACKEND can read the config file without knowing
* DataDir in advance.)
*/
SetConfigOption("data_directory", DataDir, PGC_POSTMASTER, PGC_S_OVERRIDE);
/*
* Now read the config file a second time, allowing any settings in the
* PG_AUTOCONF_FILENAME file to take effect. (This is pretty ugly, but
* since we have to determine the DataDir before we can find the autoconf
* file, the alternatives seem worse.)
*/
ProcessConfigFile(PGC_POSTMASTER);
/*
* If timezone_abbreviations wasn't set in the configuration file, install
* the default value. We do it this way because we can't safely install a
* "real" value until my_exec_path is set, which may not have happened
* when InitializeGUCOptions runs, so the bootstrap default value cannot
* be the real desired default.
*/
pg_timezone_abbrev_initialize();
/*
* Figure out where pg_hba.conf is, and make sure the path is absolute.
*/
if (HbaFileName)
fname = make_absolute_path(HbaFileName);
else if (configdir)
{
fname = guc_malloc(FATAL,
strlen(configdir) + strlen(HBA_FILENAME) + 2);
sprintf(fname, "%s/%s", configdir, HBA_FILENAME);
}
else
{
write_stderr("%s does not know where to find the \"hba\" configuration file.\n"
"This can be specified as \"hba_file\" in \"%s\", "
"or by the -D invocation option, or by the "
"PGDATA environment variable.\n",
progname, ConfigFileName);
return false;
}
SetConfigOption("hba_file", fname, PGC_POSTMASTER, PGC_S_OVERRIDE);
free(fname);
/*
* Likewise for pg_ident.conf.
*/
if (IdentFileName)
fname = make_absolute_path(IdentFileName);
else if (configdir)
{
fname = guc_malloc(FATAL,
strlen(configdir) + strlen(IDENT_FILENAME) + 2);
sprintf(fname, "%s/%s", configdir, IDENT_FILENAME);
}
else
{
write_stderr("%s does not know where to find the \"ident\" configuration file.\n"
"This can be specified as \"ident_file\" in \"%s\", "
"or by the -D invocation option, or by the "
"PGDATA environment variable.\n",
progname, ConfigFileName);
return false;
}
SetConfigOption("ident_file", fname, PGC_POSTMASTER, PGC_S_OVERRIDE);
free(fname);
free(configdir);
return true;
}
5、pqinitmask
/*
* Initialize BlockSig, UnBlockSig, and StartupBlockSig.
*
* BlockSig is the set of signals to block when we are trying to block
* signals. This includes all signals we normally expect to get, but NOT
* signals that should never be turned off.
*
* StartupBlockSig is the set of signals to block during startup packet
* collection; it's essentially BlockSig minus SIGTERM, SIGQUIT, SIGALRM.
*
* UnBlockSig is the set of signals to block when we don't want to block
* signals (is this ever nonzero??)
*/
void
pqinitmask(void)
{
sigemptyset(&UnBlockSig);
/* First set all signals, then clear some. */
sigfillset(&BlockSig);
sigfillset(&StartupBlockSig);
/*
* Unmark those signals that should never be blocked. Some of these signal
* names don't exist on all platforms. Most do, but might as well ifdef
* them all for consistency...
*/
#ifdef SIGTRAP
sigdelset(&BlockSig, SIGTRAP);
sigdelset(&StartupBlockSig, SIGTRAP);
#endif
#ifdef SIGABRT
sigdelset(&BlockSig, SIGABRT);
sigdelset(&StartupBlockSig, SIGABRT);
#endif
#ifdef SIGILL
sigdelset(&BlockSig, SIGILL);
sigdelset(&StartupBlockSig, SIGILL);
#endif
#ifdef SIGFPE
sigdelset(&BlockSig, SIGFPE);
sigdelset(&StartupBlockSig, SIGFPE);
#endif
#ifdef SIGSEGV
sigdelset(&BlockSig, SIGSEGV);
sigdelset(&StartupBlockSig, SIGSEGV);
#endif
#ifdef SIGBUS
sigdelset(&BlockSig, SIGBUS);
sigdelset(&StartupBlockSig, SIGBUS);
#endif
#ifdef SIGSYS
sigdelset(&BlockSig, SIGSYS);
sigdelset(&StartupBlockSig, SIGSYS);
#endif
#ifdef SIGCONT
sigdelset(&BlockSig, SIGCONT);
sigdelset(&StartupBlockSig, SIGCONT);
#endif
/* Signals unique to startup */
#ifdef SIGQUIT
sigdelset(&StartupBlockSig, SIGQUIT);
#endif
#ifdef SIGTERM
sigdelset(&StartupBlockSig, SIGTERM);
#endif
#ifdef SIGALRM
sigdelset(&StartupBlockSig, SIGALRM);
#endif
}
6、BaseInit
/*
* Early initialization of a backend (either standalone or under postmaster).
* This happens even before InitPostgres.
*
* This is separate from InitPostgres because it is also called by auxiliary
* processes, such as the background writer process, which may not call
* InitPostgres at all.
*/
void
BaseInit(void)
{
/*
* Attach to shared memory and semaphores, and initialize our
* input/output/debugging file descriptors.
*/
InitCommunication();
DebugFileOpen();
/* Do local initialization of file, storage and buffer managers */
InitFileAccess();
smgrinit();
InitBufferPoolAccess();
}
7、InitProcess
/*
* InitProcess -- initialize a per-process data structure for this backend
*/
void
InitProcess(void)
{
PGPROC *volatile *procgloballist;
/*
* ProcGlobal should be set up already (if we are a backend, we inherit
* this by fork() or EXEC_BACKEND mechanism from the postmaster).
*/
if (ProcGlobal == NULL)
elog(PANIC, "proc header uninitialized");
if (MyProc != NULL)
elog(ERROR, "you already exist");
/* Decide which list should supply our PGPROC. */
if (IsAnyAutoVacuumProcess())
procgloballist = &ProcGlobal->autovacFreeProcs;
else if (IsBackgroundWorker)
procgloballist = &ProcGlobal->bgworkerFreeProcs;
else
procgloballist = &ProcGlobal->freeProcs;
/*
* Try to get a proc struct from the appropriate free list. If this
* fails, we must be out of PGPROC structures (not to mention semaphores).
*
* While we are holding the ProcStructLock, also copy the current shared
* estimate of spins_per_delay to local storage.
*/
SpinLockAcquire(ProcStructLock);
set_spins_per_delay(ProcGlobal->spins_per_delay);
MyProc = *procgloballist;
if (MyProc != NULL)
{
*procgloballist = (PGPROC *) MyProc->links.next;
SpinLockRelease(ProcStructLock);
}
else
{
/*
* If we reach here, all the PGPROCs are in use. This is one of the
* possible places to detect "too many backends", so give the standard
* error message. XXX do we need to give a different failure message
* in the autovacuum case?
*/
SpinLockRelease(ProcStructLock);
ereport(FATAL,
(errcode(ERRCODE_TOO_MANY_CONNECTIONS),
errmsg("sorry, too many clients already")));
}
MyPgXact = &ProcGlobal->allPgXact[MyProc->pgprocno];
/*
* Cross-check that the PGPROC is of the type we expect; if this were not
* the case, it would get returned to the wrong list.
*/
Assert(MyProc->procgloballist == procgloballist);
/*
* Now that we have a PGPROC, mark ourselves as an active postmaster
* child; this is so that the postmaster can detect it if we exit without
* cleaning up. (XXX autovac launcher currently doesn't participate in
* this; it probably should.)
*/
if (IsUnderPostmaster && !IsAutoVacuumLauncherProcess())
MarkPostmasterChildActive();
/*
* Initialize all fields of MyProc, except for those previously
* initialized by InitProcGlobal.
*/
SHMQueueElemInit(&(MyProc->links));
MyProc->waitStatus = STATUS_OK;
MyProc->lxid = InvalidLocalTransactionId;
MyProc->fpVXIDLock = false;
MyProc->fpLocalTransactionId = InvalidLocalTransactionId;
MyPgXact->xid = InvalidTransactionId;
MyPgXact->xmin = InvalidTransactionId;
MyProc->pid = MyProcPid;
/* backendId, databaseId and roleId will be filled in later */
MyProc->backendId = InvalidBackendId;
MyProc->databaseId = InvalidOid;
MyProc->roleId = InvalidOid;
MyProc->isBackgroundWorker = IsBackgroundWorker;
MyPgXact->delayChkpt = false;
MyPgXact->vacuumFlags = 0;
/* NB -- autovac launcher intentionally does not set IS_AUTOVACUUM */
if (IsAutoVacuumWorkerProcess())
MyPgXact->vacuumFlags |= PROC_IS_AUTOVACUUM;
MyProc->lwWaiting = false;
MyProc->lwWaitMode = 0;
MyProc->waitLock = NULL;
MyProc->waitProcLock = NULL;
#ifdef USE_ASSERT_CHECKING
{
int i;
/* Last process should have released all locks. */
for (i = 0; i < NUM_LOCK_PARTITIONS; i++)
Assert(SHMQueueEmpty(&(MyProc->myProcLocks[i])));
}
#endif
MyProc->recoveryConflictPending = false;
/* Initialize fields for sync rep */
MyProc->waitLSN = 0;
MyProc->syncRepState = SYNC_REP_NOT_WAITING;
SHMQueueElemInit(&(MyProc->syncRepLinks));
/* Initialize fields for group XID clearing. */
MyProc->procArrayGroupMember = false;
MyProc->procArrayGroupMemberXid = InvalidTransactionId;
pg_atomic_init_u32(&MyProc->procArrayGroupNext, INVALID_PGPROCNO);
/* Check that group locking fields are in a proper initial state. */
Assert(MyProc->lockGroupLeader == NULL);
Assert(dlist_is_empty(&MyProc->lockGroupMembers));
/* Initialize wait event information. */
MyProc->wait_event_info = 0;
/* Initialize fields for group transaction status update. */
MyProc->clogGroupMember = false;
MyProc->clogGroupMemberXid = InvalidTransactionId;
MyProc->clogGroupMemberXidStatus = TRANSACTION_STATUS_IN_PROGRESS;
MyProc->clogGroupMemberPage = -1;
MyProc->clogGroupMemberLsn = InvalidXLogRecPtr;
pg_atomic_init_u32(&MyProc->clogGroupNext, INVALID_PGPROCNO);
/*
* Acquire ownership of the PGPROC's latch, so that we can use WaitLatch
* on it. That allows us to repoint the process latch, which so far
* points to process local one, to the shared one.
*/
OwnLatch(&MyProc->procLatch);
SwitchToSharedLatch();
/*
* We might be reusing a semaphore that belonged to a failed process. So
* be careful and reinitialize its value here. (This is not strictly
* necessary anymore, but seems like a good idea for cleanliness.)
*/
PGSemaphoreReset(MyProc->sem);
/*
* Arrange to clean up at backend exit.
*/
on_shmem_exit(ProcKill, 0);
/*
* Now that we have a PGPROC, we could try to acquire locks, so initialize
* local state needed for LWLocks, and the deadlock checker.
*/
InitLWLockAccess();
InitDeadLockChecking();
}
8、InitPostgres
/* --------------------------------
* InitPostgres
* Initialize POSTGRES.
*
* The database can be specified by name, using the in_dbname parameter, or by
* OID, using the dboid parameter. In the latter case, the actual database
* name can be returned to the caller in out_dbname. If out_dbname isn't
* NULL, it must point to a buffer of size NAMEDATALEN.
*
* Similarly, the username can be passed by name, using the username parameter,
* or by OID using the useroid parameter.
*
* In bootstrap mode no parameters are used. The autovacuum launcher process
* doesn't use any parameters either, because it only goes far enough to be
* able to read pg_database; it doesn't connect to any particular database.
* In walsender mode only username is used.
*
* As of PostgreSQL 8.2, we expect InitProcess() was already called, so we
* already have a PGPROC struct ... but it's not completely filled in yet.
*
* Note:
* Be very careful with the order of calls in the InitPostgres function.
* --------------------------------
*/
void
InitPostgres(const char *in_dbname, Oid dboid, const char *username,
Oid useroid, char *out_dbname, bool override_allow_connections)
{
bool bootstrap = IsBootstrapProcessingMode();
bool am_superuser;
char *fullpath;
char dbname[NAMEDATALEN];
elog(DEBUG3, "InitPostgres");
/*
* Add my PGPROC struct to the ProcArray.
*
* Once I have done this, I am visible to other backends!
*/
InitProcessPhase2();
/*
* Initialize my entry in the shared-invalidation manager's array of
* per-backend data.
*
* Sets up MyBackendId, a unique backend identifier.
*/
MyBackendId = InvalidBackendId;
SharedInvalBackendInit(false);
if (MyBackendId > MaxBackends || MyBackendId <= 0)
elog(FATAL, "bad backend ID: %d", MyBackendId);
/* Now that we have a BackendId, we can participate in ProcSignal */
ProcSignalInit(MyBackendId);
/*
* Also set up timeout handlers needed for backend operation. We need
* these in every case except bootstrap.
*/
if (!bootstrap)
{
RegisterTimeout(DEADLOCK_TIMEOUT, CheckDeadLockAlert);
RegisterTimeout(STATEMENT_TIMEOUT, StatementTimeoutHandler);
RegisterTimeout(LOCK_TIMEOUT, LockTimeoutHandler);
RegisterTimeout(IDLE_IN_TRANSACTION_SESSION_TIMEOUT,
IdleInTransactionSessionTimeoutHandler);
}
/*
* bufmgr needs another initialization call too
*/
InitBufferPoolBackend();
/*
* Initialize local process's access to XLOG.
*/
if (IsUnderPostmaster)
{
/*
* The postmaster already started the XLOG machinery, but we need to
* call InitXLOGAccess(), if the system isn't in hot-standby mode.
* This is handled by calling RecoveryInProgress and ignoring the
* result.
*/
(void) RecoveryInProgress();
}
else
{
/*
* We are either a bootstrap process or a standalone backend. Either
* way, start up the XLOG machinery, and register to have it closed
* down at exit.
*
* We don't yet have an aux-process resource owner, but StartupXLOG
* and ShutdownXLOG will need one. Hence, create said resource owner
* (and register a callback to clean it up after ShutdownXLOG runs).
*/
CreateAuxProcessResourceOwner();
StartupXLOG();
/* Release (and warn about) any buffer pins leaked in StartupXLOG */
ReleaseAuxProcessResources(true);
/* Reset CurrentResourceOwner to nothing for the moment */
CurrentResourceOwner = NULL;
on_shmem_exit(ShutdownXLOG, 0);
}
/*
* Initialize the relation cache and the system catalog caches. Note that
* no catalog access happens here; we only set up the hashtable structure.
* We must do this before starting a transaction because transaction abort
* would try to touch these hashtables.
*/
RelationCacheInitialize();
InitCatalogCache();
InitPlanCache();
/* Initialize portal manager */
EnablePortalManager();
/* Initialize stats collection --- must happen before first xact */
if (!bootstrap)
pgstat_initialize();
/*
* Load relcache entries for the shared system catalogs. This must create
* at least entries for pg_database and catalogs used for authentication.
*/
RelationCacheInitializePhase2();
/*
* Set up process-exit callback to do pre-shutdown cleanup. This is the
* first before_shmem_exit callback we register; thus, this will be the
* last thing we do before low-level modules like the buffer manager begin
* to close down. We need to have this in place before we begin our first
* transaction --- if we fail during the initialization transaction, as is
* entirely possible, we need the AbortTransaction call to clean up.
*/
before_shmem_exit(ShutdownPostgres, 0);
/* The autovacuum launcher is done here */
if (IsAutoVacuumLauncherProcess())
{
/* report this backend in the PgBackendStatus array */
pgstat_bestart();
return;
}
/*
* Start a new transaction here before first access to db, and get a
* snapshot. We don't have a use for the snapshot itself, but we're
* interested in the secondary effect that it sets RecentGlobalXmin. (This
* is critical for anything that reads heap pages, because HOT may decide
* to prune them even if the process doesn't attempt to modify any
* tuples.)
*/
if (!bootstrap)
{
/* statement_timestamp must be set for timeouts to work correctly */
SetCurrentStatementStartTimestamp();
StartTransactionCommand();
/*
* transaction_isolation will have been set to the default by the
* above. If the default is "serializable", and we are in hot
* standby, we will fail if we don't change it to something lower.
* Fortunately, "read committed" is plenty good enough.
*/
XactIsoLevel = XACT_READ_COMMITTED;
(void) GetTransactionSnapshot();
}
/*
* Perform client authentication if necessary, then figure out our
* postgres user ID, and see if we are a superuser.
*
* In standalone mode and in autovacuum worker processes, we use a fixed
* ID, otherwise we figure it out from the authenticated user name.
*/
if (bootstrap || IsAutoVacuumWorkerProcess())
{
InitializeSessionUserIdStandalone();
am_superuser = true;
}
else if (!IsUnderPostmaster)
{
InitializeSessionUserIdStandalone();
am_superuser = true;
if (!ThereIsAtLeastOneRole())
ereport(WARNING,
(errcode(ERRCODE_UNDEFINED_OBJECT),
errmsg("no roles are defined in this database system"),
errhint("You should immediately run CREATE USER \"%s\" SUPERUSER;.",
username != NULL ? username : "postgres")));
}
else if (IsBackgroundWorker)
{
if (username == NULL && !OidIsValid(useroid))
{
InitializeSessionUserIdStandalone();
am_superuser = true;
}
else
{
InitializeSessionUserId(username, useroid);
am_superuser = superuser();
}
}
else
{
/* normal multiuser case */
Assert(MyProcPort != NULL);
PerformAuthentication(MyProcPort);
InitializeSessionUserId(username, useroid);
am_superuser = superuser();
}
/*
* If we're trying to shut down, only superusers can connect, and new
* replication connections are not allowed.
*/
if ((!am_superuser || am_walsender) &&
MyProcPort != NULL &&
MyProcPort->canAcceptConnections == CAC_WAITBACKUP)
{
if (am_walsender)
ereport(FATAL,
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
errmsg("new replication connections are not allowed during database shutdown")));
else
ereport(FATAL,
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
errmsg("must be superuser to connect during database shutdown")));
}
/*
* Binary upgrades only allowed super-user connections
*/
if (IsBinaryUpgrade && !am_superuser)
{
ereport(FATAL,
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
errmsg("must be superuser to connect in binary upgrade mode")));
}
/*
* The last few connection slots are reserved for superusers. Although
* replication connections currently require superuser privileges, we
* don't allow them to consume the reserved slots, which are intended for
* interactive use.
*/
if ((!am_superuser || am_walsender) &&
ReservedBackends > 0 &&
!HaveNFreeProcs(ReservedBackends))
ereport(FATAL,
(errcode(ERRCODE_TOO_MANY_CONNECTIONS),
errmsg("remaining connection slots are reserved for non-replication superuser connections")));
/* Check replication permissions needed for walsender processes. */
if (am_walsender)
{
Assert(!bootstrap);
if (!superuser() && !has_rolreplication(GetUserId()))
ereport(FATAL,
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
errmsg("must be superuser or replication role to start walsender")));
}
/*
* If this is a plain walsender only supporting physical replication, we
* don't want to connect to any particular database. Just finish the
* backend startup by processing any options from the startup packet, and
* we're done.
*/
if (am_walsender && !am_db_walsender)
{
/* process any options passed in the startup packet */
if (MyProcPort != NULL)
process_startup_options(MyProcPort, am_superuser);
/* Apply PostAuthDelay as soon as we've read all options */
if (PostAuthDelay > 0)
pg_usleep(PostAuthDelay * 1000000L);
/* initialize client encoding */
InitializeClientEncoding();
/* report this backend in the PgBackendStatus array */
pgstat_bestart();
/* close the transaction we started above */
CommitTransactionCommand();
return;
}
/*
* Set up the global variables holding database id and default tablespace.
* But note we won't actually try to touch the database just yet.
*
* We take a shortcut in the bootstrap case, otherwise we have to look up
* the db's entry in pg_database.
*/
if (bootstrap)
{
MyDatabaseId = TemplateDbOid;
MyDatabaseTableSpace = DEFAULTTABLESPACE_OID;
}
else if (in_dbname != NULL)
{
HeapTuple tuple;
Form_pg_database dbform;
tuple = GetDatabaseTuple(in_dbname);
if (!HeapTupleIsValid(tuple))
ereport(FATAL,
(errcode(ERRCODE_UNDEFINED_DATABASE),
errmsg("database \"%s\" does not exist", in_dbname)));
dbform = (Form_pg_database) GETSTRUCT(tuple);
MyDatabaseId = HeapTupleGetOid(tuple);
MyDatabaseTableSpace = dbform->dattablespace;
/* take database name from the caller, just for paranoia */
strlcpy(dbname, in_dbname, sizeof(dbname));
}
else if (OidIsValid(dboid))
{
/* caller specified database by OID */
HeapTuple tuple;
Form_pg_database dbform;
tuple = GetDatabaseTupleByOid(dboid);
if (!HeapTupleIsValid(tuple))
ereport(FATAL,
(errcode(ERRCODE_UNDEFINED_DATABASE),
errmsg("database %u does not exist", dboid)));
dbform = (Form_pg_database) GETSTRUCT(tuple);
MyDatabaseId = HeapTupleGetOid(tuple);
MyDatabaseTableSpace = dbform->dattablespace;
Assert(MyDatabaseId == dboid);
strlcpy(dbname, NameStr(dbform->datname), sizeof(dbname));
/* pass the database name back to the caller */
if (out_dbname)
strcpy(out_dbname, dbname);
}
else
{
/*
* If this is a background worker not bound to any particular
* database, we're done now. Everything that follows only makes sense
* if we are bound to a specific database. We do need to close the
* transaction we started before returning.
*/
if (!bootstrap)
{
pgstat_bestart();
CommitTransactionCommand();
}
return;
}
/*
* Now, take a writer's lock on the database we are trying to connect to.
* If there is a concurrently running DROP DATABASE on that database, this
* will block us until it finishes (and has committed its update of
* pg_database).
*
* Note that the lock is not held long, only until the end of this startup
* transaction. This is OK since we will advertise our use of the
* database in the ProcArray before dropping the lock (in fact, that's the
* next thing to do). Anyone trying a DROP DATABASE after this point will
* see us in the array once they have the lock. Ordering is important for
* this because we don't want to advertise ourselves as being in this
* database until we have the lock; otherwise we create what amounts to a
* deadlock with CountOtherDBBackends().
*
* Note: use of RowExclusiveLock here is reasonable because we envision
* our session as being a concurrent writer of the database. If we had a
* way of declaring a session as being guaranteed-read-only, we could use
* AccessShareLock for such sessions and thereby not conflict against
* CREATE DATABASE.
*/
if (!bootstrap)
LockSharedObject(DatabaseRelationId, MyDatabaseId, 0,
RowExclusiveLock);
/*
* Now we can mark our PGPROC entry with the database ID.
*
* We assume this is an atomic store so no lock is needed; though actually
* things would work fine even if it weren't atomic. Anyone searching the
* ProcArray for this database's ID should hold the database lock, so they
* would not be executing concurrently with this store. A process looking
* for another database's ID could in theory see a chance match if it read
* a partially-updated databaseId value; but as long as all such searches
* wait and retry, as in CountOtherDBBackends(), they will certainly see
* the correct value on their next try.
*/
MyProc->databaseId = MyDatabaseId;
/*
* We established a catalog snapshot while reading pg_authid and/or
* pg_database; but until we have set up MyDatabaseId, we won't react to
* incoming sinval messages for unshared catalogs, so we won't realize it
* if the snapshot has been invalidated. Assume it's no good anymore.
*/
InvalidateCatalogSnapshot();
/*
* Recheck pg_database to make sure the target database hasn't gone away.
* If there was a concurrent DROP DATABASE, this ensures we will die
* cleanly without creating a mess.
*/
if (!bootstrap)
{
HeapTuple tuple;
tuple = GetDatabaseTuple(dbname);
if (!HeapTupleIsValid(tuple) ||
MyDatabaseId != HeapTupleGetOid(tuple) ||
MyDatabaseTableSpace != ((Form_pg_database) GETSTRUCT(tuple))->dattablespace)
ereport(FATAL,
(errcode(ERRCODE_UNDEFINED_DATABASE),
errmsg("database \"%s\" does not exist", dbname),
errdetail("It seems to have just been dropped or renamed.")));
}
/*
* Now we should be able to access the database directory safely. Verify
* it's there and looks reasonable.
*/
fullpath = GetDatabasePath(MyDatabaseId, MyDatabaseTableSpace);
if (!bootstrap)
{
if (access(fullpath, F_OK) == -1)
{
if (errno == ENOENT)
ereport(FATAL,
(errcode(ERRCODE_UNDEFINED_DATABASE),
errmsg("database \"%s\" does not exist",
dbname),
errdetail("The database subdirectory \"%s\" is missing.",
fullpath)));
else
ereport(FATAL,
(errcode_for_file_access(),
errmsg("could not access directory \"%s\": %m",
fullpath)));
}
ValidatePgVersion(fullpath);
}
SetDatabasePath(fullpath);
/*
* It's now possible to do real access to the system catalogs.
*
* Load relcache entries for the system catalogs. This must create at
* least the minimum set of "nailed-in" cache entries.
*/
RelationCacheInitializePhase3();
/* set up ACL framework (so CheckMyDatabase can check permissions) */
initialize_acl();
/*
* Re-read the pg_database row for our database, check permissions and set
* up database-specific GUC settings. We can't do this until all the
* database-access infrastructure is up. (Also, it wants to know if the
* user is a superuser, so the above stuff has to happen first.)
*/
if (!bootstrap)
CheckMyDatabase(dbname, am_superuser, override_allow_connections);
/*
* Now process any command-line switches and any additional GUC variable
* settings passed in the startup packet. We couldn't do this before
* because we didn't know if client is a superuser.
*/
if (MyProcPort != NULL)
process_startup_options(MyProcPort, am_superuser);
/* Process pg_db_role_setting options */
process_settings(MyDatabaseId, GetSessionUserId());
/* Apply PostAuthDelay as soon as we've read all options */
if (PostAuthDelay > 0)
pg_usleep(PostAuthDelay * 1000000L);
/*
* Initialize various default states that can't be set up until we've
* selected the active user and gotten the right GUC settings.
*/
/* set default namespace search path */
InitializeSearchPath();
/* initialize client encoding */
InitializeClientEncoding();
/* Initialize this backend's session state. */
InitializeSession();
/* report this backend in the PgBackendStatus array */
if (!bootstrap)
pgstat_bestart();
/* close the transaction we started above */
if (!bootstrap)
CommitTransactionCommand();
}
三、跟蹤分析
插入測試資料：
testdb=# -- 獲取pid
testdb=# select pg_backend_pid();
pg_backend_pid
----------------
1893
(1 row)
testdb=# -- 插入1行
testdb=# insert into t_insert values(23,'I am PostgresMain','I am PostgresMain','I am PostgresMain');
testdb=# -- 插入1行
insert into t_insert values(23,'I am PostgresMain','I am PostgresMain','I am PostgresMain');
（掛起）
啟動gdb，跟蹤除錯：
[root@localhost ~]# gdb -p 1893
GNU gdb (GDB) Red Hat Enterprise Linux 7.6.1-100.el7
Copyright (C) 2013 Free Software Foundation, Inc.
...
#斷點設定在迴圈中
(gdb) b postgres.c:4013
Breakpoint 1 at 0x850d26: file postgres.c, line 4013.
...
(gdb) p input_message
$7 = {data = 0x1508ef0 "insert into t_insert values(23,'I am PostgresMain','I am PostgresMain','I am PostgresMain');", len = 93, maxlen = 1024, cursor = 0}
(gdb) n
...
4135 switch (firstchar)
(gdb)
4142 SetCurrentStatementStartTimestamp();
(gdb) p firstchar
$8 = 81
...
(gdb) finish
Run till exit from #0 PostgresMain (argc=1, argv=0x1532aa8, dbname=0x1532990 "testdb", username=0x1532978 "xdb") at postgres.c:4020
#DONE!
使用gdb跟蹤postgres程式啟動過程：
[xdb@localhost ~]$ gdb postgres
...
(gdb) set follow-fork-mode child
(gdb) start
Temporary breakpoint 1 at 0x6f1735: file main.c, line 62.
Starting program: /appdb/xdb/bin/postgres
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
Temporary breakpoint 1, main (argc=1, argv=0x7fffffffe538) at main.c:62
62 bool do_check_root = true;
(gdb) b PostgresMain
Breakpoint 2 at 0x8507bb: file postgres.c, line 3631.
(gdb) del 1
No breakpoint number 1.
...
(gdb) attach 3028
Attaching to program: /appdb/xdb/bin/postgres, process 3028
...
#連線DB
[xdb@localhost ~]$ psql -d testdb
#回到gdb
#finish 直至進入postmaster.c中的PostgresMain
(gdb) finish
Run till exit from #0 ServerLoop () at postmaster.c:1704
[New process 3042]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
[Switching to Thread 0x7ffff7feb740 (LWP 3042)]
Breakpoint 2, PostgresMain (argc=1, argv=0xf28ac8, dbname=0xf289b0 "testdb", username=0xf28998 "xdb") at postgres.c:3631
3631 volatile bool send_ready_for_query = true;
(gdb) next
3632 bool disable_idle_in_transaction_timeout = false;
(gdb)
3635 if (!IsUnderPostmaster)
(gdb) p IsUnderPostmaster
$3 = true
(gdb) p dbname
$4 = 0xf289b0 "testdb"
(gdb) p username
$5 = 0xf28998 "xdb"
...
3845 MessageContext = AllocSetContextCreate(TopMemoryContext,
(gdb)
3855 row_description_context = AllocSetContextCreate(TopMemoryContext,
(gdb)
3858 MemoryContextSwitchTo(row_description_context);
(gdb)
3859 initStringInfo(&row_description_buf);
(gdb)
3860 MemoryContextSwitchTo(TopMemoryContext);
(gdb)
3865 if (!IsUnderPostmaster)
(gdb)
3890 if (sigsetjmp(local_sigjmp_buf, 1) != 0)
(gdb) p *MessageContext
$6 = {type = T_AllocSetContext, isReset = true, allowInCritSection = false, methods = 0xb8c720 <AllocSetMethods>, parent = 0xef9b90, firstchild = 0x0, prevchild = 0xf74c80, nextchild = 0xfabb50,
name = 0xb4e87c "MessageContext", ident = 0x0, reset_cbs = 0x0}
...
(gdb) n
4090 DoingCommandRead = true;
(gdb)
4095 firstchar = ReadCommand(&input_message);
(gdb)
4106 CHECK_FOR_INTERRUPTS();
(gdb)
4107 DoingCommandRead = false;
(gdb) p firstchar
$8 = 81
(gdb) p input_message
$9 = {data = 0xeff010 "insert into t_insert values(24,'I am PostgresMain','I am PostgresMain','I am PostgresMain');", len = 93, maxlen = 1024, cursor = 0}
(gdb) n
...
#DONE!
四、小結
1、資料結構：MessageContext ：Top訊息記憶體上下文；
2、處理/資料流程：程式初始化的相關邏輯。
來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/6906/viewspace-2374903/，如需轉載，請註明出處，否則將追究法律責任。
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