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本篇內容介紹了“PostgreSQL中AutoVacLauncherMain函數的實現邏輯是什么”的有關知識，在實際案例的操作過程中，不少人都會遇到這樣的困境，接下來就讓小編帶領大家學習一下如何處理這些情況吧！希望大家仔細閱讀，能夠學有所成！
宏定義
#define GetProcessingMode() Mode
#define SetProcessingMode(mode) \
do { \
AssertArg((mode) == BootstrapProcessing || \
(mode) == InitProcessing || \
(mode) == NormalProcessing); \
Mode = (mode); \
} while(0)AutoVacLauncherMain函數,autovacuum進程主循環.
/*
* Main loop for the autovacuum launcher process.
* autovacuum進程主循環
*/
NON_EXEC_STATIC void
AutoVacLauncherMain(int argc, char *argv[])
{
sigjmp_buf local_sigjmp_buf;
am_autovacuum_launcher = true;
/* Identify myself via ps */
//進程ID
init_ps_display(pgstat_get_backend_desc(B_AUTOVAC_LAUNCHER), "", "", "");
ereport(DEBUG1,
(errmsg("autovacuum launcher started")));
if (PostAuthDelay)
pg_usleep(PostAuthDelay * 1000000L);
//設置進程模式
SetProcessingMode(InitProcessing);
/*
* Set up signal handlers. We operate on databases much like a regular
* backend, so we use the same signal handling. See equivalent code in
* tcop/postgres.c.
* 設置信號控制器.
* autovacuum的執行類似于普通的后臺進程,因此使用相同的信號控制機制.
* 參考tcop/postgres.c中的代碼.
*/
pqsignal(SIGHUP, av_sighup_handler);
pqsignal(SIGINT, StatementCancelHandler);
pqsignal(SIGTERM, avl_sigterm_handler);
pqsignal(SIGQUIT, quickdie);
//建立SIGALRM控制器
InitializeTimeouts(); /* establishes SIGALRM handler */
pqsignal(SIGPIPE, SIG_IGN);//忽略SIGPIPE
pqsignal(SIGUSR1, procsignal_sigusr1_handler);
pqsignal(SIGUSR2, avl_sigusr2_handler);
pqsignal(SIGFPE, FloatExceptionHandler);
pqsignal(SIGCHLD, SIG_DFL);
/* Early initialization */
//基礎初始化
BaseInit();
/*
* 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).
* 在共享內存中創建每個后臺進程的PGPROC結構體，
* 但除了exEXEC_BACKEND這種情況，這是在SubPostmasterMain中完成的。
*/
#ifndef EXEC_BACKEND
InitProcess();
#endif
//初始化
InitPostgres(NULL, InvalidOid, NULL, InvalidOid, NULL, false);
//設置進程模式
SetProcessingMode(NormalProcessing);
/*
* Create a memory context that we will do all our work in. We do this so
* that we can reset the context during error recovery and thereby avoid
* possible memory leaks.
* 創建內存上下文.
* 之所以這樣做是因為我們可以在錯誤恢復中重置上下文,并且可以避免內存泄漏.
*/
AutovacMemCxt = AllocSetContextCreate(TopMemoryContext,
"Autovacuum Launcher",
ALLOCSET_DEFAULT_SIZES);
MemoryContextSwitchTo(AutovacMemCxt);
/*
* If an exception is encountered, processing resumes here.
* 如果出現異常,在這里重新恢復.
*
* This code is a stripped down version of PostgresMain error recovery.
* 這段代碼是PostgresMain錯誤恢復的精簡版。
*/
if (sigsetjmp(local_sigjmp_buf, 1) != 0)
{
/* since not using PG_TRY, must reset error stack by hand */
//由于沒有使用PG_TRY,這里必須手工重置錯誤.
error_context_stack = NULL;
/* Prevents interrupts while cleaning up */
//在清理期間禁用中斷
HOLD_INTERRUPTS();
/* Forget any pending QueryCancel or timeout request */
//忽略所有QueryCancel或者超時請求
disable_all_timeouts(false);
QueryCancelPending = false; /* second to avoid race condition */
/* Report the error to the server log */
//在服務器日志中記錄日志.
EmitErrorReport();
/* Abort the current transaction in order to recover */
//廢棄當前事務,以準備恢復
AbortCurrentTransaction();
/*
* Release any other resources, for the case where we were not in a
* transaction.
* 釋放任何其他資源，以防我們不在事務中。
*/
LWLockReleaseAll();
pgstat_report_wait_end();
AbortBufferIO();
UnlockBuffers();
/* this is probably dead code, but let's be safe: */
//這可能是dead code,但可以保證安全
if (AuxProcessResourceOwner)
ReleaseAuxProcessResources(false);
AtEOXact_Buffers(false);
AtEOXact_SMgr();
AtEOXact_Files(false);
AtEOXact_HashTables(false);
/*
* Now return to normal top-level context and clear ErrorContext for
* next time.
* 現在切換回正常的頂層上下文中,并為下一次的啟動清理錯誤上下文
*/
MemoryContextSwitchTo(AutovacMemCxt);
FlushErrorState();
/* Flush any leaked data in the top-level context */
//在top-level上下文刷新所有泄漏的數據
MemoryContextResetAndDeleteChildren(AutovacMemCxt);
/* don't leave dangling pointers to freed memory */
//不要留下懸空指針來釋放內存
DatabaseListCxt = NULL;
dlist_init(&DatabaseList);
/*
* Make sure pgstat also considers our stat data as gone. Note: we
* mustn't use autovac_refresh_stats here.
* 確保pgstat也認為我們的統計數據已經丟棄。
* 注意:這里不能使用autovac_refresh_stats。
*/
pgstat_clear_snapshot();
/* Now we can allow interrupts again */
//可以允許中斷了
RESUME_INTERRUPTS();
/* if in shutdown mode, no need for anything further; just go away */
//如處于shutdown模式,不需要繼續后續的工作了,跳轉到shutdown
if (got_SIGTERM)
goto shutdown;
/*
* Sleep at least 1 second after any error. We don't want to be
* filling the error logs as fast as we can.
*/
pg_usleep(1000000L);
}
/* We can now handle ereport(ERROR) */
//現在可以處理ereport(ERROR)了
PG_exception_stack = &local_sigjmp_buf;
/* must unblock signals before calling rebuild_database_list */
//在調用rebuild_database_list前不能阻塞信號
PG_SETMASK(&UnBlockSig);
/*
* Set always-secure search path. Launcher doesn't connect to a database,
* so this has no effect.
* 設置安全的搜索路徑.
* Launcher不能連接數據庫,因此并沒有什么影響.
*/
SetConfigOption("search_path", "", PGC_SUSET, PGC_S_OVERRIDE);
/*
* Force zero_damaged_pages OFF in the autovac process, even if it is set
* in postgresql.conf. We don't really want such a dangerous option being
* applied non-interactively.
* 在autovacuum進程中,強制關閉zero_damaged_pages,即時該參數在配置文件設置為ON.
* 我們真的不希望這樣一個危險的選項在無需交互的情況進行應用.
*/
SetConfigOption("zero_damaged_pages", "false", PGC_SUSET, PGC_S_OVERRIDE);
/*
* Force settable timeouts off to avoid letting these settings prevent
* regular maintenance from being executed.
* 強制關閉可設置的超時，以避免這些設置妨礙常規維護的執行。
*/
SetConfigOption("statement_timeout", "0", PGC_SUSET, PGC_S_OVERRIDE);
SetConfigOption("lock_timeout", "0", PGC_SUSET, PGC_S_OVERRIDE);
SetConfigOption("idle_in_transaction_session_timeout", "0",
PGC_SUSET, PGC_S_OVERRIDE);
/*
* Force default_transaction_isolation to READ COMMITTED. We don't want
* to pay the overhead of serializable mode, nor add any risk of causing
* deadlocks or delaying other transactions.
* 強制default_transaction_isolation為READ COMMITTED.
* 我們不希望在serializable模式下增加負擔,也不想增加導致死鎖或者其他事務延遲的風險.
*/
SetConfigOption("default_transaction_isolation", "read committed",
PGC_SUSET, PGC_S_OVERRIDE);
/*
* In emergency mode, just start a worker (unless shutdown was requested)
* and go away.
* 在緊急模式,啟動一個worker(除非已請求shutdown)
*/
if (!AutoVacuumingActive())
{
if (!got_SIGTERM)
do_start_worker();
proc_exit(0); /* done */
}
AutoVacuumShmem->av_launcherpid = MyProcPid;
/*
* Create the initial database list. The invariant we want this list to
* keep is that it's ordered by decreasing next_time. As soon as an entry
* is updated to a higher time, it will be moved to the front (which is
* correct because the only operation is to add autovacuum_naptime to the
* entry, and time always increases).
* 創建初始化數據庫鏈表.
* 我們希望這個鏈表保持不變的是它是通過減少next_time來進行排序.
* 一旦條目更新到更高的時間，它就會被移動到前面
* (這樣處理沒有問題，因為惟一的操作是向條目添加autovacuum_naptime，而時間總是會增加)。
*/
rebuild_database_list(InvalidOid);
/* loop until shutdown request */
//循環,直至請求shutdown
while (!got_SIGTERM)
{
struct timeval nap;
TimestampTz current_time = 0;
bool can_launch;
/*
* This loop is a bit different from the normal use of WaitLatch,
* because we'd like to sleep before the first launch of a child
* process. So it's WaitLatch, then ResetLatch, then check for
* wakening conditions.
* 該循環與常規的使用WaitLatch不同,因為我們希望在第一個子進程啟動前處于休眠狀態.
* 因此首先是WaitLatch,然后是ResetLatch,然后檢查并等待喚醒條件.
*/
launcher_determine_sleep(!dlist_is_empty(&AutoVacuumShmem->av_freeWorkers),
false, &nap);
/*
* Wait until naptime expires or we get some type of signal (all the
* signal handlers will wake us by calling SetLatch).
* 等待,直至naptime超時或者我們接收到某些類型的信號.
* (所有的信號控制器會通過調用SetLatch喚醒進程)
*/
(void) WaitLatch(MyLatch,
WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
(nap.tv_sec * 1000L) + (nap.tv_usec / 1000L),
WAIT_EVENT_AUTOVACUUM_MAIN);
ResetLatch(MyLatch);
/* Process sinval catchup interrupts that happened while sleeping */
//在休眠過程中,進程會捕獲相關的中斷.
ProcessCatchupInterrupt();
/* the normal shutdown case */
//shutdonw信號
if (got_SIGTERM)
break;
if (got_SIGHUP)
{
//SIGHUP信號
got_SIGHUP = false;
ProcessConfigFile(PGC_SIGHUP);
/* shutdown requested in config file? */
//在配置文件中已請求shutdown?
if (!AutoVacuumingActive())
break;
/* rebalance in case the default cost parameters changed */
//如默認的成本參數變化,則自動平衡.
LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
autovac_balance_cost();
LWLockRelease(AutovacuumLock);
/* rebuild the list in case the naptime changed */
//如naptime出現變化,重建鏈表
rebuild_database_list(InvalidOid);
}
/*
* a worker finished, or postmaster signalled failure to start a
* worker
* 某個worker已完成,或者postmaster信號出現異常無法啟動worker
*/
if (got_SIGUSR2)
{
//SIGUSR2信號
got_SIGUSR2 = false;
/* rebalance cost limits, if needed */
//如需要,重平衡成本限制
if (AutoVacuumShmem->av_signal[AutoVacRebalance])
{
LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
AutoVacuumShmem->av_signal[AutoVacRebalance] = false;
autovac_balance_cost();
LWLockRelease(AutovacuumLock);
}
if (AutoVacuumShmem->av_signal[AutoVacForkFailed])
{
/*
* If the postmaster failed to start a new worker, we sleep
* for a little while and resend the signal. The new worker's
* state is still in memory, so this is sufficient. After
* that, we restart the main loop.
* 如果postmaster無法啟動新的worker,休眠一段時間,重新發送信號.
* 新的worker的狀態仍然在內存中,因此這樣處理是OK的.
* 再次之后,重新啟動主循環.
*
* XXX should we put a limit to the number of times we retry?
* I don't think it makes much sense, because a future start
* of a worker will continue to fail in the same way.
* 是否增加重試次數的限制?XXX
* 我們不想太過敏感,因為某個worker在未來的啟動會以同樣的方式持續失敗.
*/
AutoVacuumShmem->av_signal[AutoVacForkFailed] = false;
pg_usleep(1000000L); /* 1s */
SendPostmasterSignal(PMSIGNAL_START_AUTOVAC_WORKER);
continue;
}
}
/*
* There are some conditions that we need to check before trying to
* start a worker. First, we need to make sure that there is a worker
* slot available. Second, we need to make sure that no other worker
* failed while starting up.
* 在嘗試啟動worker前,有一些條件需要檢查.
* 首先,需要確保有可用的worker slot;其次,需要確保worker在啟動時沒有出現異常.
*/
current_time = GetCurrentTimestamp();
LWLockAcquire(AutovacuumLock, LW_SHARED);
can_launch = !dlist_is_empty(&AutoVacuumShmem->av_freeWorkers);
if (AutoVacuumShmem->av_startingWorker != NULL)
{
int waittime;
WorkerInfo worker = AutoVacuumShmem->av_startingWorker;
/*
* We can't launch another worker when another one is still
* starting up (or failed while doing so), so just sleep for a bit
* more; that worker will wake us up again as soon as it's ready.
* We will only wait autovacuum_naptime seconds (up to a maximum
* of 60 seconds) for this to happen however. Note that failure
* to connect to a particular database is not a problem here,
* because the worker removes itself from the startingWorker
* pointer before trying to connect. Problems detected by the
* postmaster (like fork() failure) are also reported and handled
* differently. The only problems that may cause this code to
* fire are errors in the earlier sections of AutoVacWorkerMain,
* before the worker removes the WorkerInfo from the
* startingWorker pointer.
* 在某個worker仍然在啟動時,不能啟動新的worker,因此休眠一段時間;
* 另外一個worker在ready后會第一時間喚醒我們.
* 只需要等待autovacuum_naptime參數設置的時間(單位秒)(最大為60s).
* 注意,在這里不能夠連接一個特定的數據庫不存在任何問題,因為worker在
* 嘗試連接時,通過startingWorker指針銷毀自己.
* 通過postmaster檢測到問題(如fork()失敗)會報告并且進行不同的處理,
* 這里唯一的問題是可能導致這里的處理邏輯在AutoVacWorkerMain的早起觸發錯誤,
* 而且實在worker通過startingWorker指針清除WorkerInfo前.
*/
waittime = Min(autovacuum_naptime, 60) * 1000;
if (TimestampDifferenceExceeds(worker->wi_launchtime, current_time,
waittime))
{
LWLockRelease(AutovacuumLock);
LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
/*
* No other process can put a worker in starting mode, so if
* startingWorker is still INVALID after exchanging our lock,
* we assume it's the same one we saw above (so we don't
* recheck the launch time).
*/
if (AutoVacuumShmem->av_startingWorker != NULL)
{
worker = AutoVacuumShmem->av_startingWorker;
worker->wi_dboid = InvalidOid;
worker->wi_tableoid = InvalidOid;
worker->wi_sharedrel = false;
worker->wi_proc = NULL;
worker->wi_launchtime = 0;
dlist_push_head(&AutoVacuumShmem->av_freeWorkers,
&worker->wi_links);
AutoVacuumShmem->av_startingWorker = NULL;
elog(WARNING, "worker took too long to start; canceled");
}
}
else
can_launch = false;
}
//釋放鎖
LWLockRelease(AutovacuumLock); /* either shared or exclusive */
/* if we can't do anything, just go back to sleep */
//什么都做不了,繼續休眠
if (!can_launch)
continue;
/* We're OK to start a new worker */
//現在可以啟動新的worker
if (dlist_is_empty(&DatabaseList))
{
/*
* Special case when the list is empty: start a worker right away.
* This covers the initial case, when no database is in pgstats
* (thus the list is empty). Note that the constraints in
* launcher_determine_sleep keep us from starting workers too
* quickly (at most once every autovacuum_naptime when the list is
* empty).
* 在鏈表為空時的特殊情況:正確的啟動一個worker.
* 這涵蓋了剛初始的情況，即pgstats中沒有數據庫(因此鏈表為空)。
* 請注意，launcher_determine_sleep中的約束使我們不能過快地啟動worker
* (當鏈表為空時，最多一次autovacuum_naptime)。
*/
launch_worker(current_time);
}
else
{
/*
* because rebuild_database_list constructs a list with most
* distant adl_next_worker first, we obtain our database from the
* tail of the list.
* 因為rebuild_database_list首先用最遠的adl_next_worker構造了鏈表，
* 所以我們從鏈表的尾部獲取數據庫。
*/
avl_dbase *avdb;
avdb = dlist_tail_element(avl_dbase, adl_node, &DatabaseList);
/*
* launch a worker if next_worker is right now or it is in the
* past
* 啟動worker,如果next_worker正當其時或者已成為過去時.
*/
if (TimestampDifferenceExceeds(avdb->adl_next_worker,
current_time, 0))
launch_worker(current_time);
}
}
/* Normal exit from the autovac launcher is here */
//常規的退出.
shutdown:
ereport(DEBUG1,
(errmsg("autovacuum launcher shutting down")));
AutoVacuumShmem->av_launcherpid = 0;
proc_exit(0); /* done */
}“PostgreSQL中AutoVacLauncherMain函數的實現邏輯是什么”的內容就介紹到這里了，感謝大家的閱讀。如果想了解更多行業相關的知識可以關注億速云網站，小編將為大家輸出更多高質量的實用文章！
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