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* [PATCH] Demote PoC
@ 2020-04-10 16:01 Jehan-Guillaume de Rorthais <[email protected]>
0 siblings, 0 replies; 3+ messages in thread
From: Jehan-Guillaume de Rorthais @ 2020-04-10 16:01 UTC (permalink / raw)
---
src/backend/access/transam/xlog.c | 3 +-
src/backend/postmaster/postmaster.c | 206 ++++++++++++++++++------
src/bin/pg_controldata/pg_controldata.c | 2 +
src/bin/pg_ctl/pg_ctl.c | 105 ++++++++++++
src/include/catalog/pg_control.h | 1 +
src/include/libpq/libpq-be.h | 7 +-
src/include/utils/pidfile.h | 1 +
7 files changed, 271 insertions(+), 54 deletions(-)
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 55cac186dc..8a7f1a0855 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -8493,6 +8493,7 @@ ShutdownXLOG(int code, Datum arg)
CurrentResourceOwner = AuxProcessResourceOwner;
/* Don't be chatty in standalone mode */
+ // FIXME: what message when demoting?
ereport(IsPostmasterEnvironment ? LOG : NOTICE,
(errmsg("shutting down")));
@@ -8760,7 +8761,7 @@ CreateCheckPoint(int flags)
if (shutdown)
{
LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
- ControlFile->state = DB_SHUTDOWNING;
+ ControlFile->state = DB_SHUTDOWNING; // DEMOTING?
ControlFile->time = (pg_time_t) time(NULL);
UpdateControlFile();
LWLockRelease(ControlFileLock);
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index b4d475bb0b..465d020f9d 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -150,6 +150,9 @@
#define BACKEND_TYPE_WORKER (BACKEND_TYPE_AUTOVAC | BACKEND_TYPE_BGWORKER)
+/* file to signal demotion from primary to standby */
+#define DEMOTE_SIGNAL_FILE "demote"
+
/*
* List of active backends (or child processes anyway; we don't actually
* know whether a given child has become a backend or is still in the
@@ -269,18 +272,23 @@ typedef enum
static StartupStatusEnum StartupStatus = STARTUP_NOT_RUNNING;
/* Startup/shutdown state */
-#define NoShutdown 0
-#define SmartShutdown 1
-#define FastShutdown 2
-#define ImmediateShutdown 3
-
-static int Shutdown = NoShutdown;
+typedef enum StepDownState {
+ NoShutdown = 0, /* find better label? */
+ SmartShutdown,
+ SmartDemote,
+ FastShutdown,
+ FastDemote,
+ ImmediateShutdown
+} StepDownState;
+
+static StepDownState StepDown = NoShutdown;
+static bool DemoteSignal = false; /* true on demote request */
static bool FatalError = false; /* T if recovering from backend crash */
/*
- * We use a simple state machine to control startup, shutdown, and
- * crash recovery (which is rather like shutdown followed by startup).
+ * We use a simple state machine to control startup, shutdown, demote and
+ * crash recovery (both are rather like shutdown followed by startup).
*
* After doing all the postmaster initialization work, we enter PM_STARTUP
* state and the startup process is launched. The startup process begins by
@@ -314,7 +322,7 @@ static bool FatalError = false; /* T if recovering from backend crash */
* will not be very long).
*
* Notice that this state variable does not distinguish *why* we entered
- * states later than PM_RUN --- Shutdown and FatalError must be consulted
+ * states later than PM_RUN --- StepDown and FatalError must be consulted
* to find that out. FatalError is never true in PM_RECOVERY_* or PM_RUN
* states, nor in PM_SHUTDOWN states (because we don't enter those states
* when trying to recover from a crash). It can be true in PM_STARTUP state,
@@ -414,6 +422,8 @@ static bool RandomCancelKey(int32 *cancel_key);
static void signal_child(pid_t pid, int signal);
static bool SignalSomeChildren(int signal, int targets);
static void TerminateChildren(int signal);
+static bool CheckDemoteSignal(void);
+
#define SignalChildren(sig) SignalSomeChildren(sig, BACKEND_TYPE_ALL)
@@ -1550,7 +1560,7 @@ DetermineSleepTime(struct timeval *timeout)
* Normal case: either there are no background workers at all, or we're in
* a shutdown sequence (during which we ignore bgworkers altogether).
*/
- if (Shutdown > NoShutdown ||
+ if (StepDown > NoShutdown ||
(!StartWorkerNeeded && !HaveCrashedWorker))
{
if (AbortStartTime != 0)
@@ -1830,7 +1840,7 @@ ServerLoop(void)
*
* Note we also do this during recovery from a process crash.
*/
- if ((Shutdown >= ImmediateShutdown || (FatalError && !SendStop)) &&
+ if ((StepDown >= ImmediateShutdown || (FatalError && !SendStop)) &&
AbortStartTime != 0 &&
(now - AbortStartTime) >= SIGKILL_CHILDREN_AFTER_SECS)
{
@@ -2305,6 +2315,11 @@ retry1:
(errcode(ERRCODE_CANNOT_CONNECT_NOW),
errmsg("the database system is starting up")));
break;
+ case CAC_DEMOTE:
+ ereport(FATAL,
+ (errcode(ERRCODE_CANNOT_CONNECT_NOW),
+ errmsg("the database system is demoting")));
+ break;
case CAC_SHUTDOWN:
ereport(FATAL,
(errcode(ERRCODE_CANNOT_CONNECT_NOW),
@@ -2436,7 +2451,7 @@ canAcceptConnections(int backend_type)
CAC_state result = CAC_OK;
/*
- * Can't start backends when in startup/shutdown/inconsistent recovery
+ * Can't start backends when in startup/demote/shutdown/inconsistent recovery
* state. We treat autovac workers the same as user backends for this
* purpose. However, bgworkers are excluded from this test; we expect
* bgworker_should_start_now() decided whether the DB state allows them.
@@ -2452,7 +2467,9 @@ canAcceptConnections(int backend_type)
{
if (pmState == PM_WAIT_BACKUP)
result = CAC_WAITBACKUP; /* allow superusers only */
- else if (Shutdown > NoShutdown)
+ else if (StepDown == SmartDemote || StepDown == FastDemote)
+ return CAC_DEMOTE; /* demote is pending */
+ else if (StepDown > NoShutdown)
return CAC_SHUTDOWN; /* shutdown is pending */
else if (!FatalError &&
(pmState == PM_STARTUP ||
@@ -2683,7 +2700,8 @@ SIGHUP_handler(SIGNAL_ARGS)
PG_SETMASK(&BlockSig);
#endif
- if (Shutdown <= SmartShutdown)
+ if (StepDown == NoShutdown || StepDown == SmartShutdown ||
+ StepDown == SmartDemote)
{
ereport(LOG,
(errmsg("received SIGHUP, reloading configuration files")));
@@ -2769,26 +2787,72 @@ pmdie(SIGNAL_ARGS)
(errmsg_internal("postmaster received signal %d",
postgres_signal_arg)));
+ if (CheckDemoteSignal())
+ {
+ if (pmState != PM_RUN)
+ {
+ DemoteSignal = false;
+ unlink(DEMOTE_SIGNAL_FILE);
+ ereport(LOG,
+ (errmsg("ignoring demote signal because already in standby mode")));
+ }
+ else if (postgres_signal_arg == SIGQUIT) {
+ DemoteSignal = false;
+ ereport(WARNING,
+ (errmsg("can not demote in immediate stop mode")));
+ // FIXME: should we abort the shutdown process?
+ }
+ else
+ {
+ FILE *standby_file;
+
+ DemoteSignal = true;
+
+ /* create the standby signal file */
+ standby_file = AllocateFile(STANDBY_SIGNAL_FILE, "w");
+ if (!standby_file)
+ ereport(ERROR,
+ (errcode_for_file_access(),
+ errmsg("could not create file \"%s\": %m",
+ STANDBY_SIGNAL_FILE)));
+
+ if (FreeFile(standby_file))
+ ereport(ERROR,
+ (errcode_for_file_access(),
+ errmsg("could not write file \"%s\": %m",
+ STANDBY_SIGNAL_FILE)));
+ }
+
+ unlink(DEMOTE_SIGNAL_FILE);
+ }
+
switch (postgres_signal_arg)
{
case SIGTERM:
/*
- * Smart Shutdown:
+ * Smart Stepdown:
*
- * Wait for children to end their work, then shut down.
+ * Wait for children to end their work, then shut down or demote.
*/
- if (Shutdown >= SmartShutdown)
+ if (StepDown >= SmartShutdown)
break;
- Shutdown = SmartShutdown;
- ereport(LOG,
- (errmsg("received smart shutdown request")));
- /* Report status */
- AddToDataDirLockFile(LOCK_FILE_LINE_PM_STATUS, PM_STATUS_STOPPING);
+ if (DemoteSignal) {
+ StepDown = SmartDemote;
+ ereport(LOG, (errmsg("received smart demote request")));
+ /* Report status */
+ AddToDataDirLockFile(LOCK_FILE_LINE_PM_STATUS, PM_STATUS_DEMOTING);
+ }
+ else {
+ StepDown = SmartShutdown;
+ ereport(LOG, (errmsg("received smart shutdown request")));
+ /* Report status */
+ AddToDataDirLockFile(LOCK_FILE_LINE_PM_STATUS, PM_STATUS_STOPPING);
#ifdef USE_SYSTEMD
- sd_notify(0, "STOPPING=1");
+ sd_notify(0, "STOPPING=1");
#endif
+ }
if (pmState == PM_RUN || pmState == PM_RECOVERY ||
pmState == PM_HOT_STANDBY || pmState == PM_STARTUP)
@@ -2831,22 +2895,29 @@ pmdie(SIGNAL_ARGS)
case SIGINT:
/*
- * Fast Shutdown:
+ * Fast StepDown:
*
* Abort all children with SIGTERM (rollback active transactions
- * and exit) and shut down when they are gone.
+ * and exit) and shut down or demote when they are gone.
*/
- if (Shutdown >= FastShutdown)
+ if (StepDown >= FastShutdown)
break;
- Shutdown = FastShutdown;
- ereport(LOG,
- (errmsg("received fast shutdown request")));
- /* Report status */
- AddToDataDirLockFile(LOCK_FILE_LINE_PM_STATUS, PM_STATUS_STOPPING);
+ if (DemoteSignal) {
+ StepDown = FastDemote;
+ ereport(LOG, (errmsg("received fast demote request")));
+ /* Report status */
+ AddToDataDirLockFile(LOCK_FILE_LINE_PM_STATUS, PM_STATUS_DEMOTING);
+ }
+ else {
+ StepDown = FastShutdown;
+ ereport(LOG, (errmsg("received fast shutdown request")));
+ /* Report status */
+ AddToDataDirLockFile(LOCK_FILE_LINE_PM_STATUS, PM_STATUS_STOPPING);
#ifdef USE_SYSTEMD
- sd_notify(0, "STOPPING=1");
+ sd_notify(0, "STOPPING=1");
#endif
+ }
if (StartupPID != 0)
signal_child(StartupPID, SIGTERM);
@@ -2903,9 +2974,9 @@ pmdie(SIGNAL_ARGS)
* terminate remaining ones with SIGKILL, then exit without
* attempt to properly shut down the data base system.
*/
- if (Shutdown >= ImmediateShutdown)
+ if (StepDown >= ImmediateShutdown)
break;
- Shutdown = ImmediateShutdown;
+ StepDown = ImmediateShutdown;
ereport(LOG,
(errmsg("received immediate shutdown request")));
@@ -2967,10 +3038,11 @@ reaper(SIGNAL_ARGS)
StartupPID = 0;
/*
- * Startup process exited in response to a shutdown request (or it
- * completed normally regardless of the shutdown request).
+ * Startup process exited in response to a shutdown or demote
+ * request (or it completed normally regardless of the shutdown
+ * request).
*/
- if (Shutdown > NoShutdown &&
+ if (StepDown > NoShutdown &&
(EXIT_STATUS_0(exitstatus) || EXIT_STATUS_1(exitstatus)))
{
StartupStatus = STARTUP_NOT_RUNNING;
@@ -2984,7 +3056,7 @@ reaper(SIGNAL_ARGS)
ereport(LOG,
(errmsg("shutdown at recovery target")));
StartupStatus = STARTUP_NOT_RUNNING;
- Shutdown = SmartShutdown;
+ StepDown = SmartShutdown;
TerminateChildren(SIGTERM);
pmState = PM_WAIT_BACKENDS;
/* PostmasterStateMachine logic does the rest */
@@ -3124,7 +3196,7 @@ reaper(SIGNAL_ARGS)
* archive cycle and quit. Likewise, if we have walsender
* processes, tell them to send any remaining WAL and quit.
*/
- Assert(Shutdown > NoShutdown);
+ Assert(StepDown > NoShutdown);
/* Waken archiver for the last time */
if (PgArchPID != 0)
@@ -3484,7 +3556,7 @@ HandleChildCrash(int pid, int exitstatus, const char *procname)
* signaled children, nonzero exit status is to be expected, so don't
* clutter log.
*/
- take_action = !FatalError && Shutdown != ImmediateShutdown;
+ take_action = !FatalError && StepDown != ImmediateShutdown;
if (take_action)
{
@@ -3702,7 +3774,7 @@ HandleChildCrash(int pid, int exitstatus, const char *procname)
/* We do NOT restart the syslogger */
- if (Shutdown != ImmediateShutdown)
+ if (StepDown != ImmediateShutdown)
FatalError = true;
/* We now transit into a state of waiting for children to die */
@@ -3845,11 +3917,11 @@ PostmasterStateMachine(void)
WalReceiverPID == 0 &&
BgWriterPID == 0 &&
(CheckpointerPID == 0 ||
- (!FatalError && Shutdown < ImmediateShutdown)) &&
+ (!FatalError && StepDown < ImmediateShutdown)) &&
WalWriterPID == 0 &&
AutoVacPID == 0)
{
- if (Shutdown >= ImmediateShutdown || FatalError)
+ if (StepDown >= ImmediateShutdown || FatalError)
{
/*
* Start waiting for dead_end children to die. This state
@@ -3870,7 +3942,7 @@ PostmasterStateMachine(void)
* the regular children are gone, and it's time to tell the
* checkpointer to do a shutdown checkpoint.
*/
- Assert(Shutdown > NoShutdown);
+ Assert(StepDown > NoShutdown);
/* Start the checkpointer if not running */
if (CheckpointerPID == 0)
CheckpointerPID = StartCheckpointer();
@@ -3958,7 +4030,8 @@ PostmasterStateMachine(void)
* EOF on its input pipe, which happens when there are no more upstream
* processes.
*/
- if (Shutdown > NoShutdown && pmState == PM_NO_CHILDREN)
+ if (pmState == PM_NO_CHILDREN && (StepDown == SmartShutdown ||
+ StepDown == FastShutdown || StepDown == ImmediateShutdown))
{
if (FatalError)
{
@@ -3991,15 +4064,29 @@ PostmasterStateMachine(void)
* startup process fails, because more than likely it will just fail again
* and we will keep trying forever.
*/
- if (pmState == PM_NO_CHILDREN &&
+ if (pmState == PM_NO_CHILDREN && !DemoteSignal &&
(StartupStatus == STARTUP_CRASHED || !restart_after_crash))
ExitPostmaster(1);
+ /* Handle demote signal */
+ if (DemoteSignal && pmState == PM_NO_CHILDREN)
+ {
+ ereport(LOG, (errmsg("all server processes terminated; demoting")));
+
+ // Signal bgworkers?
+
+ StartupPID = StartupDataBase();
+ Assert(StartupPID != 0);
+ StartupStatus = STARTUP_RUNNING;
+ pmState = PM_STARTUP;
+ StepDown = NoShutdown;
+ }
+
/*
* If we need to recover from a crash, wait for all non-syslogger children
* to exit, then reset shmem and StartupDataBase.
*/
- if (FatalError && pmState == PM_NO_CHILDREN)
+ else if (FatalError && pmState == PM_NO_CHILDREN)
{
ereport(LOG,
(errmsg("all server processes terminated; reinitializing")));
@@ -5195,7 +5282,7 @@ sigusr1_handler(SIGNAL_ARGS)
* first. We don't want to go back to recovery in that case.
*/
if (CheckPostmasterSignal(PMSIGNAL_RECOVERY_STARTED) &&
- pmState == PM_STARTUP && Shutdown == NoShutdown)
+ pmState == PM_STARTUP && StepDown == NoShutdown)
{
/* WAL redo has started. We're out of reinitialization. */
FatalError = false;
@@ -5234,7 +5321,7 @@ sigusr1_handler(SIGNAL_ARGS)
pmState = PM_RECOVERY;
}
if (CheckPostmasterSignal(PMSIGNAL_BEGIN_HOT_STANDBY) &&
- pmState == PM_RECOVERY && Shutdown == NoShutdown)
+ pmState == PM_RECOVERY && StepDown == NoShutdown)
{
/*
* Likewise, start other special children as needed.
@@ -5284,7 +5371,7 @@ sigusr1_handler(SIGNAL_ARGS)
}
if (CheckPostmasterSignal(PMSIGNAL_START_AUTOVAC_LAUNCHER) &&
- Shutdown == NoShutdown)
+ StepDown == NoShutdown)
{
/*
* Start one iteration of the autovacuum daemon, even if autovacuuming
@@ -5299,7 +5386,7 @@ sigusr1_handler(SIGNAL_ARGS)
}
if (CheckPostmasterSignal(PMSIGNAL_START_AUTOVAC_WORKER) &&
- Shutdown == NoShutdown)
+ StepDown == NoShutdown)
{
/* The autovacuum launcher wants us to start a worker process. */
StartAutovacuumWorker();
@@ -5644,7 +5731,7 @@ MaybeStartWalReceiver(void)
if (WalReceiverPID == 0 &&
(pmState == PM_STARTUP || pmState == PM_RECOVERY ||
pmState == PM_HOT_STANDBY || pmState == PM_WAIT_READONLY) &&
- Shutdown == NoShutdown)
+ StepDown == NoShutdown)
{
WalReceiverPID = StartWalReceiver();
if (WalReceiverPID != 0)
@@ -6647,3 +6734,18 @@ InitPostmasterDeathWatchHandle(void)
GetLastError())));
#endif /* WIN32 */
}
+
+/*
+ * Check if a promote request appeared. Should be called by postmaster before
+ * shutting down.
+ */
+bool
+CheckDemoteSignal(void)
+{
+ struct stat stat_buf;
+
+ if (stat(DEMOTE_SIGNAL_FILE, &stat_buf) == 0)
+ return true;
+
+ return false;
+}
diff --git a/src/bin/pg_controldata/pg_controldata.c b/src/bin/pg_controldata/pg_controldata.c
index e73639df74..c144cc35d3 100644
--- a/src/bin/pg_controldata/pg_controldata.c
+++ b/src/bin/pg_controldata/pg_controldata.c
@@ -57,6 +57,8 @@ dbState(DBState state)
return _("shut down");
case DB_SHUTDOWNED_IN_RECOVERY:
return _("shut down in recovery");
+ case DB_DEMOTING:
+ return _("demoting");
case DB_SHUTDOWNING:
return _("shutting down");
case DB_IN_CRASH_RECOVERY:
diff --git a/src/bin/pg_ctl/pg_ctl.c b/src/bin/pg_ctl/pg_ctl.c
index 3c03ace7ed..0bb7d69682 100644
--- a/src/bin/pg_ctl/pg_ctl.c
+++ b/src/bin/pg_ctl/pg_ctl.c
@@ -62,6 +62,7 @@ typedef enum
RESTART_COMMAND,
RELOAD_COMMAND,
STATUS_COMMAND,
+ DEMOTE_COMMAND,
PROMOTE_COMMAND,
LOGROTATE_COMMAND,
KILL_COMMAND,
@@ -103,6 +104,7 @@ static char version_file[MAXPGPATH];
static char pid_file[MAXPGPATH];
static char backup_file[MAXPGPATH];
static char promote_file[MAXPGPATH];
+static char demote_file[MAXPGPATH];
static char logrotate_file[MAXPGPATH];
static volatile pgpid_t postmasterPID = -1;
@@ -129,6 +131,7 @@ static void do_stop(void);
static void do_restart(void);
static void do_reload(void);
static void do_status(void);
+static void do_demote(void);
static void do_promote(void);
static void do_logrotate(void);
static void do_kill(pgpid_t pid);
@@ -1029,6 +1032,103 @@ do_stop(void)
}
+static void
+do_demote(void)
+{
+ int cnt;
+ FILE *dmtfile;
+ pgpid_t pid;
+ struct stat statbuf;
+
+ pid = get_pgpid(false);
+
+ if (pid == 0) /* no pid file */
+ {
+ write_stderr(_("%s: PID file \"%s\" does not exist\n"), progname, pid_file);
+ write_stderr(_("Is server running?\n"));
+ exit(1);
+ }
+ else if (pid < 0) /* standalone backend, not postmaster */
+ {
+ pid = -pid;
+ write_stderr(_("%s: cannot demote server; "
+ "single-user server is running (PID: %ld)\n"),
+ progname, pid);
+ exit(1);
+ }
+
+ snprintf(demote_file, MAXPGPATH, "%s/demote", pg_data);
+
+ if ((dmtfile = fopen(demote_file, "w")) == NULL)
+ {
+ write_stderr(_("%s: could not create demote signal file \"%s\": %s\n"),
+ progname, demote_file, strerror(errno));
+ exit(1);
+ }
+ if (fclose(dmtfile))
+ {
+ write_stderr(_("%s: could not write demote signal file \"%s\": %s\n"),
+ progname, demote_file, strerror(errno));
+ exit(1);
+ }
+
+ if (kill((pid_t) pid, sig) != 0)
+ {
+ write_stderr(_("%s: could not send stop signal (PID: %ld): %s\n"), progname, pid,
+ strerror(errno));
+ exit(1);
+ }
+
+ if (!do_wait)
+ {
+ print_msg(_("server demoting\n"));
+ return;
+ }
+ else
+ {
+ /*
+ * If backup_label exists, an online backup is running. Warn the user
+ * that smart demote will wait for it to finish. However, if the
+ * server is in archive recovery, we're recovering from an online
+ * backup instead of performing one.
+ */
+ if (shutdown_mode == SMART_MODE &&
+ stat(backup_file, &statbuf) == 0 &&
+ get_control_dbstate() != DB_IN_ARCHIVE_RECOVERY)
+ {
+ print_msg(_("WARNING: online backup mode is active\n"
+ "Demote will not complete until pg_stop_backup() is called.\n\n"));
+ }
+
+ print_msg(_("waiting for server to demote..."));
+
+ for (cnt = 0; cnt < wait_seconds * WAITS_PER_SEC; cnt++)
+ {
+ if (get_control_dbstate() == DB_IN_ARCHIVE_RECOVERY)
+ break;
+
+ if (cnt % WAITS_PER_SEC == 0)
+ print_msg(".");
+ pg_usleep(USEC_PER_SEC / WAITS_PER_SEC);
+ }
+
+ if (get_control_dbstate() != DB_IN_ARCHIVE_RECOVERY)
+ {
+ print_msg(_(" failed\n"));
+
+ write_stderr(_("%s: server does not demote\n"), progname);
+ if (shutdown_mode == SMART_MODE)
+ write_stderr(_("HINT: The \"-m fast\" option immediately disconnects sessions rather than\n"
+ "waiting for session-initiated disconnection.\n"));
+ exit(1);
+ }
+ print_msg(_(" done\n"));
+
+ print_msg(_("server demoted\n"));
+ }
+}
+
+
/*
* restart/reload routines
*/
@@ -2452,6 +2552,8 @@ main(int argc, char **argv)
ctl_command = RELOAD_COMMAND;
else if (strcmp(argv[optind], "status") == 0)
ctl_command = STATUS_COMMAND;
+ else if (strcmp(argv[optind], "demote") == 0)
+ ctl_command = DEMOTE_COMMAND;
else if (strcmp(argv[optind], "promote") == 0)
ctl_command = PROMOTE_COMMAND;
else if (strcmp(argv[optind], "logrotate") == 0)
@@ -2559,6 +2661,9 @@ main(int argc, char **argv)
case RELOAD_COMMAND:
do_reload();
break;
+ case DEMOTE_COMMAND:
+ do_demote();
+ break;
case PROMOTE_COMMAND:
do_promote();
break;
diff --git a/src/include/catalog/pg_control.h b/src/include/catalog/pg_control.h
index de5670e538..f529f8c7bd 100644
--- a/src/include/catalog/pg_control.h
+++ b/src/include/catalog/pg_control.h
@@ -87,6 +87,7 @@ typedef enum DBState
DB_STARTUP = 0,
DB_SHUTDOWNED,
DB_SHUTDOWNED_IN_RECOVERY,
+ DB_DEMOTING,
DB_SHUTDOWNING,
DB_IN_CRASH_RECOVERY,
DB_IN_ARCHIVE_RECOVERY,
diff --git a/src/include/libpq/libpq-be.h b/src/include/libpq/libpq-be.h
index 179ebaa104..a9e27f009e 100644
--- a/src/include/libpq/libpq-be.h
+++ b/src/include/libpq/libpq-be.h
@@ -70,7 +70,12 @@ typedef struct
typedef enum CAC_state
{
- CAC_OK, CAC_STARTUP, CAC_SHUTDOWN, CAC_RECOVERY, CAC_TOOMANY,
+ CAC_OK,
+ CAC_STARTUP,
+ CAC_DEMOTE,
+ CAC_SHUTDOWN,
+ CAC_RECOVERY,
+ CAC_TOOMANY,
CAC_WAITBACKUP
} CAC_state;
diff --git a/src/include/utils/pidfile.h b/src/include/utils/pidfile.h
index 63fefe5c4c..f761d2c4ef 100644
--- a/src/include/utils/pidfile.h
+++ b/src/include/utils/pidfile.h
@@ -50,6 +50,7 @@
*/
#define PM_STATUS_STARTING "starting" /* still starting up */
#define PM_STATUS_STOPPING "stopping" /* in shutdown sequence */
+#define PM_STATUS_DEMOTING "demoting" /* demote sequence */
#define PM_STATUS_READY "ready " /* ready for connections */
#define PM_STATUS_STANDBY "standby " /* up, won't accept connections */
--
2.20.1
--MP_/9v.jdvlK+JLUeXFsf_NviJr--
^ permalink raw reply [nested|flat] 3+ messages in thread
* [PATCH] Demote PoC
@ 2020-04-10 16:01 Jehan-Guillaume de Rorthais <[email protected]>
0 siblings, 0 replies; 3+ messages in thread
From: Jehan-Guillaume de Rorthais @ 2020-04-10 16:01 UTC (permalink / raw)
Changes:
* creates a demote checkpoint
* use DB_DEMOTING state in controlfile
* try to handle subsystems init correctly during demote
* keep some sub-processes alive:
stat collector, checkpointer, bgwriter and optionally archiver or wal
senders
* add signal PMSIGNAL_DEMOTING to start the startup process after the
demote checkpoint
* ShutdownXLOG takes a boolean arg to handle demote differently
Trivial manual tests:
* make check : OK
* make check-world : OK
* start in production -> demote -> demote: OK
* start in production -> demote -> stop : OK
* start in production -> demote -> promote : NOK (2PC, see TODO)
but OK with no prepared xact.
Discuss/Todo:
* rollback prepared xact
* cancel/kill active/idle in xact R/W backends
* pg_demote() function?
* some more code reviewing around StartupXlog
* investigate snapshots shmem needs/init during recovery compare to
production
* add tap tests
* add doc
* how to handle checkpoint?
---
src/backend/access/rmgrdesc/xlogdesc.c | 9 +-
src/backend/access/transam/xlog.c | 287 +++++++++++++++---------
src/backend/postmaster/checkpointer.c | 22 ++
src/backend/postmaster/postmaster.c | 250 ++++++++++++++++-----
src/backend/storage/ipc/procsignal.c | 4 +
src/bin/pg_controldata/pg_controldata.c | 2 +
src/bin/pg_ctl/pg_ctl.c | 111 +++++++++
src/include/access/xlog.h | 18 +-
src/include/catalog/pg_control.h | 2 +
src/include/libpq/libpq-be.h | 7 +-
src/include/postmaster/bgwriter.h | 1 +
src/include/storage/pmsignal.h | 1 +
src/include/storage/procsignal.h | 1 +
src/include/utils/pidfile.h | 1 +
14 files changed, 537 insertions(+), 179 deletions(-)
diff --git a/src/backend/access/rmgrdesc/xlogdesc.c b/src/backend/access/rmgrdesc/xlogdesc.c
index 1cd97852e8..5aeaff18f8 100644
--- a/src/backend/access/rmgrdesc/xlogdesc.c
+++ b/src/backend/access/rmgrdesc/xlogdesc.c
@@ -40,7 +40,8 @@ xlog_desc(StringInfo buf, XLogReaderState *record)
uint8 info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
if (info == XLOG_CHECKPOINT_SHUTDOWN ||
- info == XLOG_CHECKPOINT_ONLINE)
+ info == XLOG_CHECKPOINT_ONLINE ||
+ info == XLOG_CHECKPOINT_DEMOTE)
{
CheckPoint *checkpoint = (CheckPoint *) rec;
@@ -65,7 +66,8 @@ xlog_desc(StringInfo buf, XLogReaderState *record)
checkpoint->oldestCommitTsXid,
checkpoint->newestCommitTsXid,
checkpoint->oldestActiveXid,
- (info == XLOG_CHECKPOINT_SHUTDOWN) ? "shutdown" : "online");
+ (info == XLOG_CHECKPOINT_SHUTDOWN) ? "shutdown" :
+ (info == XLOG_CHECKPOINT_DEMOTE)? "demote" : "online");
}
else if (info == XLOG_NEXTOID)
{
@@ -185,6 +187,9 @@ xlog_identify(uint8 info)
case XLOG_FPI_FOR_HINT:
id = "FPI_FOR_HINT";
break;
+ case XLOG_CHECKPOINT_DEMOTE:
+ id = "CHECKPOINT_DEMOTE";
+ break;
}
return id;
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index e455384b5b..0e18e546ba 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -6301,6 +6301,13 @@ CheckRequiredParameterValues(void)
/*
* This must be called ONCE during postmaster or standalone-backend startup
*/
+/*
+ * FIXME demote: part of the code here assume there's no other active
+ * processes before signal PMSIGNAL_RECOVERY_STARTED is sent.
+ *
+ * FIXME demote: rollback prepared xact during demote?
+ */
+
void
StartupXLOG(void)
{
@@ -6324,6 +6331,7 @@ StartupXLOG(void)
XLogPageReadPrivate private;
bool fast_promoted = false;
struct stat st;
+ bool is_demoting = false;
/*
* We should have an aux process resource owner to use, and we should not
@@ -6388,6 +6396,16 @@ StartupXLOG(void)
str_time(ControlFile->time))));
break;
+ case DB_DEMOTING:
+ ereport(LOG,
+ (errmsg("database system was demoted at %s",
+ str_time(ControlFile->time))));
+ is_demoting = true;
+ bgwriterLaunched = true;
+ InArchiveRecovery = true;
+ StandbyMode = true;
+ break;
+
default:
ereport(FATAL,
(errmsg("control file contains invalid database cluster state")));
@@ -6421,7 +6439,8 @@ StartupXLOG(void)
* persisted. To avoid that, fsync the entire data directory.
*/
if (ControlFile->state != DB_SHUTDOWNED &&
- ControlFile->state != DB_SHUTDOWNED_IN_RECOVERY)
+ ControlFile->state != DB_SHUTDOWNED_IN_RECOVERY &&
+ ControlFile->state != DB_DEMOTING)
{
RemoveTempXlogFiles();
SyncDataDirectory();
@@ -6678,6 +6697,9 @@ StartupXLOG(void)
}
memcpy(&checkPoint, XLogRecGetData(xlogreader), sizeof(CheckPoint));
wasShutdown = ((record->xl_info & ~XLR_INFO_MASK) == XLOG_CHECKPOINT_SHUTDOWN);
+
+ if (is_demoting)
+ Assert((record->xl_info & ~XLR_INFO_MASK) == XLOG_CHECKPOINT_DEMOTE);
}
/*
@@ -6739,9 +6761,9 @@ StartupXLOG(void)
LastRec = RecPtr = checkPointLoc;
ereport(DEBUG1,
- (errmsg_internal("redo record is at %X/%X; shutdown %s",
+ (errmsg_internal("redo record is at %X/%X; %s checkpoint",
(uint32) (checkPoint.redo >> 32), (uint32) checkPoint.redo,
- wasShutdown ? "true" : "false")));
+ wasShutdown ? "shutdown" : is_demoting? "demote": "")));
ereport(DEBUG1,
(errmsg_internal("next transaction ID: " UINT64_FORMAT "; next OID: %u",
U64FromFullTransactionId(checkPoint.nextFullXid),
@@ -6775,47 +6797,74 @@ StartupXLOG(void)
checkPoint.newestCommitTsXid);
XLogCtl->ckptFullXid = checkPoint.nextFullXid;
- /*
- * Initialize replication slots, before there's a chance to remove
- * required resources.
- */
- StartupReplicationSlots();
+ if (!is_demoting)
+ {
+ /*
+ * Initialize replication slots, before there's a chance to remove
+ * required resources.
+ */
+ StartupReplicationSlots();
- /*
- * Startup logical state, needs to be setup now so we have proper data
- * during crash recovery.
- */
- StartupReorderBuffer();
+ /*
+ * Startup logical state, needs to be setup now so we have proper data
+ * during crash recovery.
+ */
+ StartupReorderBuffer();
- /*
- * Startup MultiXact. We need to do this early to be able to replay
- * truncations.
- */
- StartupMultiXact();
+ /*
+ * Startup MultiXact. We need to do this early to be able to replay
+ * truncations.
+ */
+ StartupMultiXact();
- /*
- * Ditto for commit timestamps. Activate the facility if the setting is
- * enabled in the control file, as there should be no tracking of commit
- * timestamps done when the setting was disabled. This facility can be
- * started or stopped when replaying a XLOG_PARAMETER_CHANGE record.
- */
- if (ControlFile->track_commit_timestamp)
- StartupCommitTs();
+ /*
+ * Ditto for commit timestamps. Activate the facility if the setting is
+ * enabled in the control file, as there should be no tracking of commit
+ * timestamps done when the setting was disabled. This facility can be
+ * started or stopped when replaying a XLOG_PARAMETER_CHANGE record.
+ */
+ if (ControlFile->track_commit_timestamp)
+ StartupCommitTs();
- /*
- * Recover knowledge about replay progress of known replication partners.
- */
- StartupReplicationOrigin();
+ /*
+ * Recover knowledge about replay progress of known replication partners.
+ */
+ StartupReplicationOrigin();
- /*
- * Initialize unlogged LSN. On a clean shutdown, it's restored from the
- * control file. On recovery, all unlogged relations are blown away, so
- * the unlogged LSN counter can be reset too.
- */
- if (ControlFile->state == DB_SHUTDOWNED)
- XLogCtl->unloggedLSN = ControlFile->unloggedLSN;
- else
- XLogCtl->unloggedLSN = FirstNormalUnloggedLSN;
+ /*
+ * Initialize unlogged LSN. On a clean shutdown, it's restored from the
+ * control file. On recovery, all unlogged relations are blown away, so
+ * the unlogged LSN counter can be reset too.
+ */
+ if (ControlFile->state == DB_SHUTDOWNED)
+ XLogCtl->unloggedLSN = ControlFile->unloggedLSN;
+ else
+ XLogCtl->unloggedLSN = FirstNormalUnloggedLSN;
+
+ /*
+ * Copy any missing timeline history files between 'now' and the recovery
+ * target timeline from archive to pg_wal. While we don't need those files
+ * ourselves - the history file of the recovery target timeline covers all
+ * the previous timelines in the history too - a cascading standby server
+ * might be interested in them. Or, if you archive the WAL from this
+ * server to a different archive than the master, it'd be good for all the
+ * history files to get archived there after failover, so that you can use
+ * one of the old timelines as a PITR target. Timeline history files are
+ * small, so it's better to copy them unnecessarily than not copy them and
+ * regret later.
+ */
+ restoreTimeLineHistoryFiles(ThisTimeLineID, recoveryTargetTLI);
+
+ /*
+ * Before running in recovery, scan pg_twophase and fill in its status to
+ * be able to work on entries generated by redo. Doing a scan before
+ * taking any recovery action has the merit to discard any 2PC files that
+ * are newer than the first record to replay, saving from any conflicts at
+ * replay. This avoids as well any subsequent scans when doing recovery
+ * of the on-disk two-phase data.
+ */
+ restoreTwoPhaseData();
+ }
/*
* We must replay WAL entries using the same TimeLineID they were created
@@ -6824,30 +6873,6 @@ StartupXLOG(void)
*/
ThisTimeLineID = checkPoint.ThisTimeLineID;
- /*
- * Copy any missing timeline history files between 'now' and the recovery
- * target timeline from archive to pg_wal. While we don't need those files
- * ourselves - the history file of the recovery target timeline covers all
- * the previous timelines in the history too - a cascading standby server
- * might be interested in them. Or, if you archive the WAL from this
- * server to a different archive than the master, it'd be good for all the
- * history files to get archived there after failover, so that you can use
- * one of the old timelines as a PITR target. Timeline history files are
- * small, so it's better to copy them unnecessarily than not copy them and
- * regret later.
- */
- restoreTimeLineHistoryFiles(ThisTimeLineID, recoveryTargetTLI);
-
- /*
- * Before running in recovery, scan pg_twophase and fill in its status to
- * be able to work on entries generated by redo. Doing a scan before
- * taking any recovery action has the merit to discard any 2PC files that
- * are newer than the first record to replay, saving from any conflicts at
- * replay. This avoids as well any subsequent scans when doing recovery
- * of the on-disk two-phase data.
- */
- restoreTwoPhaseData();
-
lastFullPageWrites = checkPoint.fullPageWrites;
RedoRecPtr = XLogCtl->RedoRecPtr = XLogCtl->Insert.RedoRecPtr = checkPoint.redo;
@@ -6985,7 +7010,8 @@ StartupXLOG(void)
/*
* Reset pgstat data, because it may be invalid after recovery.
*/
- pgstat_reset_all();
+ if (!is_demoting)
+ pgstat_reset_all();
/*
* If there was a backup label file, it's done its job and the info
@@ -7061,8 +7087,11 @@ StartupXLOG(void)
* timestamp have already been started up and other SLRUs are not
* maintained during recovery and need not be started yet.
*/
- StartupCLOG();
- StartupSUBTRANS(oldestActiveXID);
+ if (!is_demoting)
+ {
+ StartupCLOG();
+ StartupSUBTRANS(oldestActiveXID);
+ }
/*
* If we're beginning at a shutdown checkpoint, we know that
@@ -7070,7 +7099,7 @@ StartupXLOG(void)
* empty running-xacts record and use that here and now. Recover
* additional standby state for prepared transactions.
*/
- if (wasShutdown)
+ if (wasShutdown || is_demoting)
{
RunningTransactionsData running;
TransactionId latestCompletedXid;
@@ -7093,9 +7122,10 @@ StartupXLOG(void)
running.xids = xids;
ProcArrayApplyRecoveryInfo(&running);
+ }
+ if (wasShutdown)
StandbyRecoverPreparedTransactions();
- }
}
/* Initialize resource managers */
@@ -7941,6 +7971,7 @@ StartupXLOG(void)
SpinLockAcquire(&XLogCtl->info_lck);
XLogCtl->SharedRecoveryState = RECOVERY_STATE_DONE;
+ XLogCtl->SharedHotStandbyActive = false;
SpinLockRelease(&XLogCtl->info_lck);
UpdateControlFile();
@@ -8292,7 +8323,8 @@ ReadCheckpointRecord(XLogReaderState *xlogreader, XLogRecPtr RecPtr,
}
info = record->xl_info & ~XLR_INFO_MASK;
if (info != XLOG_CHECKPOINT_SHUTDOWN &&
- info != XLOG_CHECKPOINT_ONLINE)
+ info != XLOG_CHECKPOINT_ONLINE &&
+ info != XLOG_CHECKPOINT_DEMOTE)
{
switch (whichChkpt)
{
@@ -8486,6 +8518,8 @@ GetLastSegSwitchData(XLogRecPtr *lastSwitchLSN)
void
ShutdownXLOG(int code, Datum arg)
{
+ bool isDemoting = DatumGetBool(arg);
+
/*
* We should have an aux process resource owner to use, and we should not
* be in a transaction that's installed some other resowner.
@@ -8495,36 +8529,56 @@ ShutdownXLOG(int code, Datum arg)
CurrentResourceOwner == AuxProcessResourceOwner);
CurrentResourceOwner = AuxProcessResourceOwner;
- /* Don't be chatty in standalone mode */
- ereport(IsPostmasterEnvironment ? LOG : NOTICE,
- (errmsg("shutting down")));
-
- /*
- * Signal walsenders to move to stopping state.
- */
- WalSndInitStopping();
-
- /*
- * Wait for WAL senders to be in stopping state. This prevents commands
- * from writing new WAL.
- */
- WalSndWaitStopping();
+ if (isDemoting)
+ {
+ /* Don't be chatty in standalone mode */
+ ereport(IsPostmasterEnvironment ? LOG : NOTICE,
+ (errmsg("demoting")));
- if (RecoveryInProgress())
- CreateRestartPoint(CHECKPOINT_IS_SHUTDOWN | CHECKPOINT_IMMEDIATE);
+ /*
+ * FIXME demote: avoiding checkpoint?
+ * A checkpoint is probably running during a demote action. If
+ * we don't want to wait for the checkpoint during the demote,
+ * we might need to cancel it as it will not be able to write
+ * to the WAL after the demote.
+ */
+ CreateCheckPoint(CHECKPOINT_IS_DEMOTE | CHECKPOINT_IMMEDIATE);
+ LocalRecoveryInProgress = true;
+ }
else
{
+ /* Don't be chatty in standalone mode */
+ ereport(IsPostmasterEnvironment ? LOG : NOTICE,
+ (errmsg("shutting down")));
+
/*
- * If archiving is enabled, rotate the last XLOG file so that all the
- * remaining records are archived (postmaster wakes up the archiver
- * process one more time at the end of shutdown). The checkpoint
- * record will go to the next XLOG file and won't be archived (yet).
+ * Signal walsenders to move to stopping state.
*/
- if (XLogArchivingActive() && XLogArchiveCommandSet())
- RequestXLogSwitch(false);
+ WalSndInitStopping();
+
+ /*
+ * Wait for WAL senders to be in stopping state. This prevents commands
+ * from writing new WAL.
+ */
+ WalSndWaitStopping();
- CreateCheckPoint(CHECKPOINT_IS_SHUTDOWN | CHECKPOINT_IMMEDIATE);
+ if (RecoveryInProgress())
+ CreateRestartPoint(CHECKPOINT_IS_SHUTDOWN | CHECKPOINT_IMMEDIATE);
+ else
+ {
+ /*
+ * If archiving is enabled, rotate the last XLOG file so that all the
+ * remaining records are archived (postmaster wakes up the archiver
+ * process one more time at the end of shutdown). The checkpoint
+ * record will go to the next XLOG file and won't be archived (yet).
+ */
+ if (XLogArchivingActive() && XLogArchiveCommandSet())
+ RequestXLogSwitch(false);
+
+ CreateCheckPoint(CHECKPOINT_IS_SHUTDOWN | CHECKPOINT_IMMEDIATE);
+ }
}
+
ShutdownCLOG();
ShutdownCommitTs();
ShutdownSUBTRANS();
@@ -8537,9 +8591,10 @@ ShutdownXLOG(int code, Datum arg)
static void
LogCheckpointStart(int flags, bool restartpoint)
{
- elog(LOG, "%s starting:%s%s%s%s%s%s%s%s",
+ elog(LOG, "%s starting:%s%s%s%s%s%s%s%s%s",
restartpoint ? "restartpoint" : "checkpoint",
(flags & CHECKPOINT_IS_SHUTDOWN) ? " shutdown" : "",
+ (flags & CHECKPOINT_IS_DEMOTE) ? " demote" : "",
(flags & CHECKPOINT_END_OF_RECOVERY) ? " end-of-recovery" : "",
(flags & CHECKPOINT_IMMEDIATE) ? " immediate" : "",
(flags & CHECKPOINT_FORCE) ? " force" : "",
@@ -8675,6 +8730,7 @@ UpdateCheckPointDistanceEstimate(uint64 nbytes)
*
* flags is a bitwise OR of the following:
* CHECKPOINT_IS_SHUTDOWN: checkpoint is for database shutdown.
+ * CHECKPOINT_IS_DEMOTE: checkpoint is for demote.
* CHECKPOINT_END_OF_RECOVERY: checkpoint is for end of WAL recovery.
* CHECKPOINT_IMMEDIATE: finish the checkpoint ASAP,
* ignoring checkpoint_completion_target parameter.
@@ -8703,6 +8759,7 @@ void
CreateCheckPoint(int flags)
{
bool shutdown;
+ bool demote;
CheckPoint checkPoint;
XLogRecPtr recptr;
XLogSegNo _logSegNo;
@@ -8723,6 +8780,14 @@ CreateCheckPoint(int flags)
else
shutdown = false;
+ /*
+ * An demote checkpoint is kind of a shutdown checkpoint as well
+ */
+ if (flags & CHECKPOINT_IS_DEMOTE)
+ demote = true;
+ else
+ demote = false;
+
/* sanity check */
if (RecoveryInProgress() && (flags & CHECKPOINT_END_OF_RECOVERY) == 0)
elog(ERROR, "can't create a checkpoint during recovery");
@@ -8760,10 +8825,10 @@ CreateCheckPoint(int flags)
*/
START_CRIT_SECTION();
- if (shutdown)
+ if (shutdown || demote)
{
LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
- ControlFile->state = DB_SHUTDOWNING;
+ ControlFile->state = demote? DB_DEMOTING:DB_SHUTDOWNING;
ControlFile->time = (pg_time_t) time(NULL);
UpdateControlFile();
LWLockRelease(ControlFileLock);
@@ -8809,7 +8874,7 @@ CreateCheckPoint(int flags)
* avoid inserting duplicate checkpoints when the system is idle.
*/
if ((flags & (CHECKPOINT_IS_SHUTDOWN | CHECKPOINT_END_OF_RECOVERY |
- CHECKPOINT_FORCE)) == 0)
+ CHECKPOINT_IS_DEMOTE | CHECKPOINT_FORCE)) == 0)
{
if (last_important_lsn == ControlFile->checkPoint)
{
@@ -8980,7 +9045,7 @@ CreateCheckPoint(int flags)
* If we are shutting down, or Startup process is completing crash
* recovery we don't need to write running xact data.
*/
- if (!shutdown && XLogStandbyInfoActive())
+ if (!(shutdown||demote) && XLogStandbyInfoActive())
LogStandbySnapshot();
START_CRIT_SECTION();
@@ -8990,20 +9055,23 @@ CreateCheckPoint(int flags)
*/
XLogBeginInsert();
XLogRegisterData((char *) (&checkPoint), sizeof(checkPoint));
- recptr = XLogInsert(RM_XLOG_ID,
- shutdown ? XLOG_CHECKPOINT_SHUTDOWN :
- XLOG_CHECKPOINT_ONLINE);
+ if (demote)
+ recptr = XLogInsert(RM_XLOG_ID, XLOG_CHECKPOINT_DEMOTE);
+ else if (shutdown)
+ recptr = XLogInsert(RM_XLOG_ID, XLOG_CHECKPOINT_SHUTDOWN);
+ else
+ recptr = XLogInsert(RM_XLOG_ID, XLOG_CHECKPOINT_ONLINE);
XLogFlush(recptr);
/*
- * We mustn't write any new WAL after a shutdown checkpoint, or it will be
- * overwritten at next startup. No-one should even try, this just allows
- * sanity-checking. In the case of an end-of-recovery checkpoint, we want
- * to just temporarily disable writing until the system has exited
- * recovery.
+ * We mustn't write any new WAL after a shutdown or demote checkpoint, or
+ * it will be overwritten at next startup. No-one should even try, this
+ * just allows sanity-checking. In the case of an end-of-recovery
+ * checkpoint, we want to just temporarily disable writing until the system
+ * has exited recovery.
*/
- if (shutdown)
+ if (shutdown||demote)
{
if (flags & CHECKPOINT_END_OF_RECOVERY)
LocalXLogInsertAllowed = -1; /* return to "check" state */
@@ -9015,9 +9083,10 @@ CreateCheckPoint(int flags)
* We now have ProcLastRecPtr = start of actual checkpoint record, recptr
* = end of actual checkpoint record.
*/
- if (shutdown && checkPoint.redo != ProcLastRecPtr)
+ if ((shutdown||demote) && checkPoint.redo != ProcLastRecPtr)
ereport(PANIC,
- (errmsg("concurrent write-ahead log activity while database system is shutting down")));
+ (errmsg("concurrent write-ahead log activity while database system is %s",
+ shutdown? "shutting down":"demoting")));
/*
* Remember the prior checkpoint's redo ptr for
@@ -9087,7 +9156,7 @@ CreateCheckPoint(int flags)
* Make more log segments if needed. (Do this after recycling old log
* segments, since that may supply some of the needed files.)
*/
- if (!shutdown)
+ if (!(shutdown||demote))
PreallocXlogFiles(recptr);
/*
diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.c
index 624a3238b8..cf8ea2a601 100644
--- a/src/backend/postmaster/checkpointer.c
+++ b/src/backend/postmaster/checkpointer.c
@@ -52,6 +52,7 @@
#include "storage/fd.h"
#include "storage/ipc.h"
#include "storage/lwlock.h"
+#include "storage/pmsignal.h"
#include "storage/proc.h"
#include "storage/procsignal.h"
#include "storage/shmem.h"
@@ -151,6 +152,7 @@ double CheckPointCompletionTarget = 0.5;
* Private state
*/
static bool ckpt_active = false;
+static volatile sig_atomic_t demoteRequestPending = false;
/* these values are valid when ckpt_active is true: */
static pg_time_t ckpt_start_time;
@@ -552,6 +554,14 @@ HandleCheckpointerInterrupts(void)
*/
UpdateSharedMemoryConfig();
}
+ if (demoteRequestPending)
+ {
+ demoteRequestPending = false;
+ /* Close down the database */
+ ShutdownXLOG(0, BoolGetDatum(true));
+ SendPostmasterSignal(PMSIGNAL_DEMOTING);
+ /* no need to exit the checkpointer during demote */
+ }
if (ShutdownRequestPending)
{
/*
@@ -680,6 +690,7 @@ CheckpointWriteDelay(int flags, double progress)
* in which case we just try to catch up as quickly as possible.
*/
if (!(flags & CHECKPOINT_IMMEDIATE) &&
+ !demoteRequestPending &&
!ShutdownRequestPending &&
!ImmediateCheckpointRequested() &&
IsCheckpointOnSchedule(progress))
@@ -812,6 +823,17 @@ IsCheckpointOnSchedule(double progress)
* --------------------------------
*/
+/* SIGUSR1: set flag to demote */
+void
+ReqCheckpointDemoteHandler(SIGNAL_ARGS)
+{
+ int save_errno = errno;
+
+ demoteRequestPending = true;
+
+ errno = save_errno;
+}
+
/* SIGINT: set flag to run a normal checkpoint right away */
static void
ReqCheckpointHandler(SIGNAL_ARGS)
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index b4d475bb0b..d5cc63f697 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -150,6 +150,9 @@
#define BACKEND_TYPE_WORKER (BACKEND_TYPE_AUTOVAC | BACKEND_TYPE_BGWORKER)
+/* file to signal demotion from primary to standby */
+#define DEMOTE_SIGNAL_FILE "demote"
+
/*
* List of active backends (or child processes anyway; we don't actually
* know whether a given child has become a backend or is still in the
@@ -269,18 +272,23 @@ typedef enum
static StartupStatusEnum StartupStatus = STARTUP_NOT_RUNNING;
/* Startup/shutdown state */
-#define NoShutdown 0
-#define SmartShutdown 1
-#define FastShutdown 2
-#define ImmediateShutdown 3
-
-static int Shutdown = NoShutdown;
+typedef enum StepDownState {
+ NoShutdown = 0, /* find better label? */
+ SmartShutdown,
+ SmartDemote,
+ FastShutdown,
+ FastDemote,
+ ImmediateShutdown
+} StepDownState;
+
+static StepDownState StepDown = NoShutdown;
+static bool DemoteSignal = false; /* true on demote request */
static bool FatalError = false; /* T if recovering from backend crash */
/*
- * We use a simple state machine to control startup, shutdown, and
- * crash recovery (which is rather like shutdown followed by startup).
+ * We use a simple state machine to control startup, shutdown, demote and
+ * crash recovery (both are rather like shutdown followed by startup).
*
* After doing all the postmaster initialization work, we enter PM_STARTUP
* state and the startup process is launched. The startup process begins by
@@ -314,7 +322,7 @@ static bool FatalError = false; /* T if recovering from backend crash */
* will not be very long).
*
* Notice that this state variable does not distinguish *why* we entered
- * states later than PM_RUN --- Shutdown and FatalError must be consulted
+ * states later than PM_RUN --- StepDown and FatalError must be consulted
* to find that out. FatalError is never true in PM_RECOVERY_* or PM_RUN
* states, nor in PM_SHUTDOWN states (because we don't enter those states
* when trying to recover from a crash). It can be true in PM_STARTUP state,
@@ -414,6 +422,8 @@ static bool RandomCancelKey(int32 *cancel_key);
static void signal_child(pid_t pid, int signal);
static bool SignalSomeChildren(int signal, int targets);
static void TerminateChildren(int signal);
+static bool CheckDemoteSignal(void);
+
#define SignalChildren(sig) SignalSomeChildren(sig, BACKEND_TYPE_ALL)
@@ -1550,7 +1560,7 @@ DetermineSleepTime(struct timeval *timeout)
* Normal case: either there are no background workers at all, or we're in
* a shutdown sequence (during which we ignore bgworkers altogether).
*/
- if (Shutdown > NoShutdown ||
+ if (StepDown > NoShutdown ||
(!StartWorkerNeeded && !HaveCrashedWorker))
{
if (AbortStartTime != 0)
@@ -1830,7 +1840,7 @@ ServerLoop(void)
*
* Note we also do this during recovery from a process crash.
*/
- if ((Shutdown >= ImmediateShutdown || (FatalError && !SendStop)) &&
+ if ((StepDown >= ImmediateShutdown || (FatalError && !SendStop)) &&
AbortStartTime != 0 &&
(now - AbortStartTime) >= SIGKILL_CHILDREN_AFTER_SECS)
{
@@ -2305,6 +2315,11 @@ retry1:
(errcode(ERRCODE_CANNOT_CONNECT_NOW),
errmsg("the database system is starting up")));
break;
+ case CAC_DEMOTE:
+ ereport(FATAL,
+ (errcode(ERRCODE_CANNOT_CONNECT_NOW),
+ errmsg("the database system is demoting")));
+ break;
case CAC_SHUTDOWN:
ereport(FATAL,
(errcode(ERRCODE_CANNOT_CONNECT_NOW),
@@ -2436,7 +2451,7 @@ canAcceptConnections(int backend_type)
CAC_state result = CAC_OK;
/*
- * Can't start backends when in startup/shutdown/inconsistent recovery
+ * Can't start backends when in startup/demote/shutdown/inconsistent recovery
* state. We treat autovac workers the same as user backends for this
* purpose. However, bgworkers are excluded from this test; we expect
* bgworker_should_start_now() decided whether the DB state allows them.
@@ -2452,7 +2467,9 @@ canAcceptConnections(int backend_type)
{
if (pmState == PM_WAIT_BACKUP)
result = CAC_WAITBACKUP; /* allow superusers only */
- else if (Shutdown > NoShutdown)
+ else if (StepDown == SmartDemote || StepDown == FastDemote)
+ return CAC_DEMOTE; /* demote is pending */
+ else if (StepDown > NoShutdown)
return CAC_SHUTDOWN; /* shutdown is pending */
else if (!FatalError &&
(pmState == PM_STARTUP ||
@@ -2683,7 +2700,8 @@ SIGHUP_handler(SIGNAL_ARGS)
PG_SETMASK(&BlockSig);
#endif
- if (Shutdown <= SmartShutdown)
+ if (StepDown == NoShutdown || StepDown == SmartShutdown ||
+ StepDown == SmartDemote)
{
ereport(LOG,
(errmsg("received SIGHUP, reloading configuration files")));
@@ -2769,26 +2787,81 @@ pmdie(SIGNAL_ARGS)
(errmsg_internal("postmaster received signal %d",
postgres_signal_arg)));
+ if (CheckDemoteSignal())
+ {
+ if (pmState != PM_RUN)
+ {
+ DemoteSignal = false;
+ unlink(DEMOTE_SIGNAL_FILE);
+ ereport(LOG,
+ (errmsg("ignoring demote signal because already in standby mode")));
+ goto out;
+ }
+ else if (postgres_signal_arg == SIGQUIT)
+ {
+ DemoteSignal = false;
+ unlink(DEMOTE_SIGNAL_FILE);
+ ereport(WARNING,
+ (errmsg("can not demote in immediate stop mode")));
+ goto out;
+ }
+ else
+ {
+ FILE *standby_file;
+
+ DemoteSignal = true;
+
+ unlink(DEMOTE_SIGNAL_FILE);
+
+ /* create the standby signal file */
+ standby_file = AllocateFile(STANDBY_SIGNAL_FILE, "w");
+ if (!standby_file)
+ {
+ ereport(ERROR,
+ (errcode_for_file_access(),
+ errmsg("could not create file \"%s\": %m",
+ STANDBY_SIGNAL_FILE)));
+ goto out;
+ }
+
+ if (FreeFile(standby_file))
+ {
+ ereport(ERROR,
+ (errcode_for_file_access(),
+ errmsg("could not write file \"%s\": %m",
+ STANDBY_SIGNAL_FILE)));
+ goto out;
+ }
+ }
+ }
+
switch (postgres_signal_arg)
{
case SIGTERM:
/*
- * Smart Shutdown:
+ * Smart Stepdown:
*
- * Wait for children to end their work, then shut down.
+ * Wait for children to end their work, then shut down or demote.
*/
- if (Shutdown >= SmartShutdown)
+ if (StepDown >= SmartShutdown)
break;
- Shutdown = SmartShutdown;
- ereport(LOG,
- (errmsg("received smart shutdown request")));
- /* Report status */
- AddToDataDirLockFile(LOCK_FILE_LINE_PM_STATUS, PM_STATUS_STOPPING);
+ if (DemoteSignal) {
+ StepDown = SmartDemote;
+ ereport(LOG, (errmsg("received smart demote request")));
+ /* Report status */
+ AddToDataDirLockFile(LOCK_FILE_LINE_PM_STATUS, PM_STATUS_DEMOTING);
+ }
+ else {
+ StepDown = SmartShutdown;
+ ereport(LOG, (errmsg("received smart shutdown request")));
+ /* Report status */
+ AddToDataDirLockFile(LOCK_FILE_LINE_PM_STATUS, PM_STATUS_STOPPING);
#ifdef USE_SYSTEMD
- sd_notify(0, "STOPPING=1");
+ sd_notify(0, "STOPPING=1");
#endif
+ }
if (pmState == PM_RUN || pmState == PM_RECOVERY ||
pmState == PM_HOT_STANDBY || pmState == PM_STARTUP)
@@ -2831,22 +2904,29 @@ pmdie(SIGNAL_ARGS)
case SIGINT:
/*
- * Fast Shutdown:
+ * Fast StepDown:
*
* Abort all children with SIGTERM (rollback active transactions
- * and exit) and shut down when they are gone.
+ * and exit) and shut down or demote when they are gone.
*/
- if (Shutdown >= FastShutdown)
+ if (StepDown >= FastShutdown)
break;
- Shutdown = FastShutdown;
- ereport(LOG,
- (errmsg("received fast shutdown request")));
- /* Report status */
- AddToDataDirLockFile(LOCK_FILE_LINE_PM_STATUS, PM_STATUS_STOPPING);
+ if (DemoteSignal) {
+ StepDown = FastDemote;
+ ereport(LOG, (errmsg("received fast demote request")));
+ /* Report status */
+ AddToDataDirLockFile(LOCK_FILE_LINE_PM_STATUS, PM_STATUS_DEMOTING);
+ }
+ else {
+ StepDown = FastShutdown;
+ ereport(LOG, (errmsg("received fast shutdown request")));
+ /* Report status */
+ AddToDataDirLockFile(LOCK_FILE_LINE_PM_STATUS, PM_STATUS_STOPPING);
#ifdef USE_SYSTEMD
- sd_notify(0, "STOPPING=1");
+ sd_notify(0, "STOPPING=1");
#endif
+ }
if (StartupPID != 0)
signal_child(StartupPID, SIGTERM);
@@ -2903,9 +2983,9 @@ pmdie(SIGNAL_ARGS)
* terminate remaining ones with SIGKILL, then exit without
* attempt to properly shut down the data base system.
*/
- if (Shutdown >= ImmediateShutdown)
+ if (StepDown >= ImmediateShutdown)
break;
- Shutdown = ImmediateShutdown;
+ StepDown = ImmediateShutdown;
ereport(LOG,
(errmsg("received immediate shutdown request")));
@@ -2929,6 +3009,7 @@ pmdie(SIGNAL_ARGS)
break;
}
+out:
#ifdef WIN32
PG_SETMASK(&UnBlockSig);
#endif
@@ -2967,10 +3048,11 @@ reaper(SIGNAL_ARGS)
StartupPID = 0;
/*
- * Startup process exited in response to a shutdown request (or it
- * completed normally regardless of the shutdown request).
+ * Startup process exited in response to a shutdown or demote
+ * request (or it completed normally regardless of the shutdown
+ * request).
*/
- if (Shutdown > NoShutdown &&
+ if (StepDown > NoShutdown &&
(EXIT_STATUS_0(exitstatus) || EXIT_STATUS_1(exitstatus)))
{
StartupStatus = STARTUP_NOT_RUNNING;
@@ -2984,7 +3066,7 @@ reaper(SIGNAL_ARGS)
ereport(LOG,
(errmsg("shutdown at recovery target")));
StartupStatus = STARTUP_NOT_RUNNING;
- Shutdown = SmartShutdown;
+ StepDown = SmartShutdown;
TerminateChildren(SIGTERM);
pmState = PM_WAIT_BACKENDS;
/* PostmasterStateMachine logic does the rest */
@@ -3124,7 +3206,7 @@ reaper(SIGNAL_ARGS)
* archive cycle and quit. Likewise, if we have walsender
* processes, tell them to send any remaining WAL and quit.
*/
- Assert(Shutdown > NoShutdown);
+ Assert(StepDown > NoShutdown);
/* Waken archiver for the last time */
if (PgArchPID != 0)
@@ -3484,7 +3566,7 @@ HandleChildCrash(int pid, int exitstatus, const char *procname)
* signaled children, nonzero exit status is to be expected, so don't
* clutter log.
*/
- take_action = !FatalError && Shutdown != ImmediateShutdown;
+ take_action = !FatalError && StepDown != ImmediateShutdown;
if (take_action)
{
@@ -3702,7 +3784,7 @@ HandleChildCrash(int pid, int exitstatus, const char *procname)
/* We do NOT restart the syslogger */
- if (Shutdown != ImmediateShutdown)
+ if (StepDown != ImmediateShutdown)
FatalError = true;
/* We now transit into a state of waiting for children to die */
@@ -3845,11 +3927,11 @@ PostmasterStateMachine(void)
WalReceiverPID == 0 &&
BgWriterPID == 0 &&
(CheckpointerPID == 0 ||
- (!FatalError && Shutdown < ImmediateShutdown)) &&
+ (!FatalError && StepDown < ImmediateShutdown)) &&
WalWriterPID == 0 &&
AutoVacPID == 0)
{
- if (Shutdown >= ImmediateShutdown || FatalError)
+ if (StepDown >= ImmediateShutdown || FatalError)
{
/*
* Start waiting for dead_end children to die. This state
@@ -3863,6 +3945,15 @@ PostmasterStateMachine(void)
* FatalError state.
*/
}
+ /* Handle demote signal */
+ else if (DemoteSignal)
+ {
+ ereport(LOG, (errmsg("all backend processes terminated; demoting")));
+
+ SendProcSignal(CheckpointerPID, PROCSIG_CHECKPOINTER_DEMOTING, InvalidBackendId);
+ pmState = PM_STARTUP;
+ StepDown = NoShutdown;
+ }
else
{
/*
@@ -3870,7 +3961,7 @@ PostmasterStateMachine(void)
* the regular children are gone, and it's time to tell the
* checkpointer to do a shutdown checkpoint.
*/
- Assert(Shutdown > NoShutdown);
+ Assert(StepDown > NoShutdown);
/* Start the checkpointer if not running */
if (CheckpointerPID == 0)
CheckpointerPID = StartCheckpointer();
@@ -3958,7 +4049,8 @@ PostmasterStateMachine(void)
* EOF on its input pipe, which happens when there are no more upstream
* processes.
*/
- if (Shutdown > NoShutdown && pmState == PM_NO_CHILDREN)
+ if (pmState == PM_NO_CHILDREN && (StepDown == SmartShutdown ||
+ StepDown == FastShutdown || StepDown == ImmediateShutdown))
{
if (FatalError)
{
@@ -3991,7 +4083,7 @@ PostmasterStateMachine(void)
* startup process fails, because more than likely it will just fail again
* and we will keep trying forever.
*/
- if (pmState == PM_NO_CHILDREN &&
+ if (pmState == PM_NO_CHILDREN && !DemoteSignal &&
(StartupStatus == STARTUP_CRASHED || !restart_after_crash))
ExitPostmaster(1);
@@ -5188,6 +5280,17 @@ sigusr1_handler(SIGNAL_ARGS)
StartWorkerNeeded = true;
}
+ /* Demoting: start the Startup Process */
+ if (CheckPostmasterSignal(PMSIGNAL_DEMOTING) &&
+ pmState == PM_STARTUP && StepDown == NoShutdown)
+ {
+ if (!XLogArchivingAlways())
+ signal_child(PgArchPID, SIGQUIT);
+ StartupPID = StartupDataBase();
+ Assert(StartupPID != 0);
+ StartupStatus = STARTUP_RUNNING;
+ }
+
/*
* RECOVERY_STARTED and BEGIN_HOT_STANDBY signals are ignored in
* unexpected states. If the startup process quickly starts up, completes
@@ -5195,7 +5298,7 @@ sigusr1_handler(SIGNAL_ARGS)
* first. We don't want to go back to recovery in that case.
*/
if (CheckPostmasterSignal(PMSIGNAL_RECOVERY_STARTED) &&
- pmState == PM_STARTUP && Shutdown == NoShutdown)
+ pmState == PM_STARTUP && StepDown == NoShutdown)
{
/* WAL redo has started. We're out of reinitialization. */
FatalError = false;
@@ -5205,17 +5308,27 @@ sigusr1_handler(SIGNAL_ARGS)
* Crank up the background tasks. It doesn't matter if this fails,
* we'll just try again later.
*/
- Assert(CheckpointerPID == 0);
- CheckpointerPID = StartCheckpointer();
- Assert(BgWriterPID == 0);
- BgWriterPID = StartBackgroundWriter();
+ if (!DemoteSignal)
+ {
+ Assert(CheckpointerPID == 0);
+ Assert(BgWriterPID == 0);
+ Assert(PgArchPID == 0);
+
+ CheckpointerPID = StartCheckpointer();
+ }
+ else
+ {
+ Assert(CheckpointerPID);
+ }
+
+ if (BgWriterPID == 0)
+ BgWriterPID = StartBackgroundWriter();
/*
* Start the archiver if we're responsible for (re-)archiving received
* files.
*/
- Assert(PgArchPID == 0);
- if (XLogArchivingAlways())
+ if (PgArchPID == 0 && XLogArchivingAlways())
PgArchPID = pgarch_start();
/*
@@ -5226,6 +5339,7 @@ sigusr1_handler(SIGNAL_ARGS)
if (!EnableHotStandby)
{
AddToDataDirLockFile(LOCK_FILE_LINE_PM_STATUS, PM_STATUS_STANDBY);
+ DemoteSignal = false;
#ifdef USE_SYSTEMD
sd_notify(0, "READY=1");
#endif
@@ -5234,13 +5348,15 @@ sigusr1_handler(SIGNAL_ARGS)
pmState = PM_RECOVERY;
}
if (CheckPostmasterSignal(PMSIGNAL_BEGIN_HOT_STANDBY) &&
- pmState == PM_RECOVERY && Shutdown == NoShutdown)
+ pmState == PM_RECOVERY && StepDown == NoShutdown)
{
/*
* Likewise, start other special children as needed.
*/
- Assert(PgStatPID == 0);
- PgStatPID = pgstat_start();
+ if (!DemoteSignal)
+ Assert(PgStatPID == 0);
+ if(PgStatPID == 0)
+ PgStatPID = pgstat_start();
ereport(LOG,
(errmsg("database system is ready to accept read only connections")));
@@ -5252,6 +5368,7 @@ sigusr1_handler(SIGNAL_ARGS)
#endif
pmState = PM_HOT_STANDBY;
+ DemoteSignal = false;
/* Some workers may be scheduled to start now */
StartWorkerNeeded = true;
}
@@ -5284,7 +5401,7 @@ sigusr1_handler(SIGNAL_ARGS)
}
if (CheckPostmasterSignal(PMSIGNAL_START_AUTOVAC_LAUNCHER) &&
- Shutdown == NoShutdown)
+ StepDown == NoShutdown)
{
/*
* Start one iteration of the autovacuum daemon, even if autovacuuming
@@ -5299,7 +5416,7 @@ sigusr1_handler(SIGNAL_ARGS)
}
if (CheckPostmasterSignal(PMSIGNAL_START_AUTOVAC_WORKER) &&
- Shutdown == NoShutdown)
+ StepDown == NoShutdown)
{
/* The autovacuum launcher wants us to start a worker process. */
StartAutovacuumWorker();
@@ -5644,7 +5761,7 @@ MaybeStartWalReceiver(void)
if (WalReceiverPID == 0 &&
(pmState == PM_STARTUP || pmState == PM_RECOVERY ||
pmState == PM_HOT_STANDBY || pmState == PM_WAIT_READONLY) &&
- Shutdown == NoShutdown)
+ StepDown == NoShutdown)
{
WalReceiverPID = StartWalReceiver();
if (WalReceiverPID != 0)
@@ -6647,3 +6764,18 @@ InitPostmasterDeathWatchHandle(void)
GetLastError())));
#endif /* WIN32 */
}
+
+/*
+ * Check if a promote request appeared. Should be called by postmaster before
+ * shutting down.
+ */
+bool
+CheckDemoteSignal(void)
+{
+ struct stat stat_buf;
+
+ if (stat(DEMOTE_SIGNAL_FILE, &stat_buf) == 0)
+ return true;
+
+ return false;
+}
diff --git a/src/backend/storage/ipc/procsignal.c b/src/backend/storage/ipc/procsignal.c
index 4fa385b0ec..1903f4db2a 100644
--- a/src/backend/storage/ipc/procsignal.c
+++ b/src/backend/storage/ipc/procsignal.c
@@ -28,6 +28,7 @@
#include "storage/shmem.h"
#include "storage/sinval.h"
#include "tcop/tcopprot.h"
+#include "postmaster/bgwriter.h"
/*
* The SIGUSR1 signal is multiplexed to support signaling multiple event
@@ -585,6 +586,9 @@ procsignal_sigusr1_handler(SIGNAL_ARGS)
if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN))
RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN);
+ if (CheckProcSignal(PROCSIG_CHECKPOINTER_DEMOTING))
+ ReqCheckpointDemoteHandler(PROCSIG_CHECKPOINTER_DEMOTING);
+
SetLatch(MyLatch);
latch_sigusr1_handler();
diff --git a/src/bin/pg_controldata/pg_controldata.c b/src/bin/pg_controldata/pg_controldata.c
index e73639df74..c144cc35d3 100644
--- a/src/bin/pg_controldata/pg_controldata.c
+++ b/src/bin/pg_controldata/pg_controldata.c
@@ -57,6 +57,8 @@ dbState(DBState state)
return _("shut down");
case DB_SHUTDOWNED_IN_RECOVERY:
return _("shut down in recovery");
+ case DB_DEMOTING:
+ return _("demoting");
case DB_SHUTDOWNING:
return _("shutting down");
case DB_IN_CRASH_RECOVERY:
diff --git a/src/bin/pg_ctl/pg_ctl.c b/src/bin/pg_ctl/pg_ctl.c
index 3c03ace7ed..79bb42f7e7 100644
--- a/src/bin/pg_ctl/pg_ctl.c
+++ b/src/bin/pg_ctl/pg_ctl.c
@@ -62,6 +62,7 @@ typedef enum
RESTART_COMMAND,
RELOAD_COMMAND,
STATUS_COMMAND,
+ DEMOTE_COMMAND,
PROMOTE_COMMAND,
LOGROTATE_COMMAND,
KILL_COMMAND,
@@ -103,6 +104,7 @@ static char version_file[MAXPGPATH];
static char pid_file[MAXPGPATH];
static char backup_file[MAXPGPATH];
static char promote_file[MAXPGPATH];
+static char demote_file[MAXPGPATH];
static char logrotate_file[MAXPGPATH];
static volatile pgpid_t postmasterPID = -1;
@@ -129,6 +131,7 @@ static void do_stop(void);
static void do_restart(void);
static void do_reload(void);
static void do_status(void);
+static void do_demote(void);
static void do_promote(void);
static void do_logrotate(void);
static void do_kill(pgpid_t pid);
@@ -1029,6 +1032,109 @@ do_stop(void)
}
+static void
+do_demote(void)
+{
+ int cnt;
+ FILE *dmtfile;
+ pgpid_t pid;
+ struct stat statbuf;
+
+ pid = get_pgpid(false);
+
+ if (pid == 0) /* no pid file */
+ {
+ write_stderr(_("%s: PID file \"%s\" does not exist\n"), progname, pid_file);
+ write_stderr(_("Is server running?\n"));
+ exit(1);
+ }
+ else if (pid < 0) /* standalone backend, not postmaster */
+ {
+ pid = -pid;
+ write_stderr(_("%s: cannot demote server; "
+ "single-user server is running (PID: %ld)\n"),
+ progname, pid);
+ exit(1);
+ }
+ if (shutdown_mode == IMMEDIATE_MODE)
+ {
+ write_stderr(_("%s: cannot demote server using immediate mode"),
+ progname);
+ exit(1);
+ }
+
+ snprintf(demote_file, MAXPGPATH, "%s/demote", pg_data);
+
+ if ((dmtfile = fopen(demote_file, "w")) == NULL)
+ {
+ write_stderr(_("%s: could not create demote signal file \"%s\": %s\n"),
+ progname, demote_file, strerror(errno));
+ exit(1);
+ }
+ if (fclose(dmtfile))
+ {
+ write_stderr(_("%s: could not write demote signal file \"%s\": %s\n"),
+ progname, demote_file, strerror(errno));
+ exit(1);
+ }
+
+ if (kill((pid_t) pid, sig) != 0)
+ {
+ write_stderr(_("%s: could not send stop signal (PID: %ld): %s\n"), progname, pid,
+ strerror(errno));
+ exit(1);
+ }
+
+ if (!do_wait)
+ {
+ print_msg(_("server demoting\n"));
+ return;
+ }
+ else
+ {
+ /*
+ * If backup_label exists, an online backup is running. Warn the user
+ * that smart demote will wait for it to finish. However, if the
+ * server is in archive recovery, we're recovering from an online
+ * backup instead of performing one.
+ */
+ if (shutdown_mode == SMART_MODE &&
+ stat(backup_file, &statbuf) == 0 &&
+ get_control_dbstate() != DB_IN_ARCHIVE_RECOVERY)
+ {
+ print_msg(_("WARNING: online backup mode is active\n"
+ "Demote will not complete until pg_stop_backup() is called.\n\n"));
+ }
+
+ print_msg(_("waiting for server to demote..."));
+
+ for (cnt = 0; cnt < wait_seconds * WAITS_PER_SEC; cnt++)
+ {
+ if (get_control_dbstate() == DB_IN_ARCHIVE_RECOVERY)
+ break;
+
+ if (cnt % WAITS_PER_SEC == 0)
+ print_msg(".");
+ pg_usleep(USEC_PER_SEC / WAITS_PER_SEC);
+ }
+
+ if (get_control_dbstate() != DB_IN_ARCHIVE_RECOVERY)
+ {
+ print_msg(_(" failed\n"));
+
+ write_stderr(_("%s: server does not demote\n"), progname);
+ if (shutdown_mode == SMART_MODE)
+ write_stderr(_("HINT: The \"-m fast\" option immediately disconnects sessions rather than\n"
+ "waiting for session-initiated disconnection.\n"));
+ exit(1);
+ }
+ print_msg(_(" done\n"));
+
+ print_msg(_("server demoted\n"));
+ }
+}
+
+
/*
* restart/reload routines
*/
@@ -2452,6 +2558,8 @@ main(int argc, char **argv)
ctl_command = RELOAD_COMMAND;
else if (strcmp(argv[optind], "status") == 0)
ctl_command = STATUS_COMMAND;
+ else if (strcmp(argv[optind], "demote") == 0)
+ ctl_command = DEMOTE_COMMAND;
else if (strcmp(argv[optind], "promote") == 0)
ctl_command = PROMOTE_COMMAND;
else if (strcmp(argv[optind], "logrotate") == 0)
@@ -2559,6 +2667,9 @@ main(int argc, char **argv)
case RELOAD_COMMAND:
do_reload();
break;
+ case DEMOTE_COMMAND:
+ do_demote();
+ break;
case PROMOTE_COMMAND:
do_promote();
break;
diff --git a/src/include/access/xlog.h b/src/include/access/xlog.h
index 77ac4e785f..ff0119046e 100644
--- a/src/include/access/xlog.h
+++ b/src/include/access/xlog.h
@@ -219,18 +219,20 @@ extern bool XLOG_DEBUG;
/* These directly affect the behavior of CreateCheckPoint and subsidiaries */
#define CHECKPOINT_IS_SHUTDOWN 0x0001 /* Checkpoint is for shutdown */
-#define CHECKPOINT_END_OF_RECOVERY 0x0002 /* Like shutdown checkpoint, but
+#define CHECKPOINT_IS_DEMOTE 0x0002 /* Like shutdown checkpoint, but
+ * issued at end of WAL production */
+#define CHECKPOINT_END_OF_RECOVERY 0x0004 /* Like shutdown checkpoint, but
* issued at end of WAL recovery */
-#define CHECKPOINT_IMMEDIATE 0x0004 /* Do it without delays */
-#define CHECKPOINT_FORCE 0x0008 /* Force even if no activity */
-#define CHECKPOINT_FLUSH_ALL 0x0010 /* Flush all pages, including those
+#define CHECKPOINT_IMMEDIATE 0x0008 /* Do it without delays */
+#define CHECKPOINT_FORCE 0x0010 /* Force even if no activity */
+#define CHECKPOINT_FLUSH_ALL 0x0020 /* Flush all pages, including those
* belonging to unlogged tables */
/* These are important to RequestCheckpoint */
-#define CHECKPOINT_WAIT 0x0020 /* Wait for completion */
-#define CHECKPOINT_REQUESTED 0x0040 /* Checkpoint request has been made */
+#define CHECKPOINT_WAIT 0x0040 /* Wait for completion */
+#define CHECKPOINT_REQUESTED 0x0080 /* Checkpoint request has been made */
/* These indicate the cause of a checkpoint request */
-#define CHECKPOINT_CAUSE_XLOG 0x0080 /* XLOG consumption */
-#define CHECKPOINT_CAUSE_TIME 0x0100 /* Elapsed time */
+#define CHECKPOINT_CAUSE_XLOG 0x0100 /* XLOG consumption */
+#define CHECKPOINT_CAUSE_TIME 0x0200 /* Elapsed time */
/*
* Flag bits for the record being inserted, set using XLogSetRecordFlags().
diff --git a/src/include/catalog/pg_control.h b/src/include/catalog/pg_control.h
index de5670e538..b38671ae52 100644
--- a/src/include/catalog/pg_control.h
+++ b/src/include/catalog/pg_control.h
@@ -76,6 +76,7 @@ typedef struct CheckPoint
#define XLOG_END_OF_RECOVERY 0x90
#define XLOG_FPI_FOR_HINT 0xA0
#define XLOG_FPI 0xB0
+#define XLOG_CHECKPOINT_DEMOTE 0xC0
/*
@@ -87,6 +88,7 @@ typedef enum DBState
DB_STARTUP = 0,
DB_SHUTDOWNED,
DB_SHUTDOWNED_IN_RECOVERY,
+ DB_DEMOTING,
DB_SHUTDOWNING,
DB_IN_CRASH_RECOVERY,
DB_IN_ARCHIVE_RECOVERY,
diff --git a/src/include/libpq/libpq-be.h b/src/include/libpq/libpq-be.h
index 179ebaa104..a9e27f009e 100644
--- a/src/include/libpq/libpq-be.h
+++ b/src/include/libpq/libpq-be.h
@@ -70,7 +70,12 @@ typedef struct
typedef enum CAC_state
{
- CAC_OK, CAC_STARTUP, CAC_SHUTDOWN, CAC_RECOVERY, CAC_TOOMANY,
+ CAC_OK,
+ CAC_STARTUP,
+ CAC_DEMOTE,
+ CAC_SHUTDOWN,
+ CAC_RECOVERY,
+ CAC_TOOMANY,
CAC_WAITBACKUP
} CAC_state;
diff --git a/src/include/postmaster/bgwriter.h b/src/include/postmaster/bgwriter.h
index 0a5708b32e..4d4f0ea1dd 100644
--- a/src/include/postmaster/bgwriter.h
+++ b/src/include/postmaster/bgwriter.h
@@ -41,5 +41,6 @@ extern Size CheckpointerShmemSize(void);
extern void CheckpointerShmemInit(void);
extern bool FirstCallSinceLastCheckpoint(void);
+extern void ReqCheckpointDemoteHandler(SIGNAL_ARGS);
#endif /* _BGWRITER_H */
diff --git a/src/include/storage/pmsignal.h b/src/include/storage/pmsignal.h
index 56c5ec4481..1c5baf3b68 100644
--- a/src/include/storage/pmsignal.h
+++ b/src/include/storage/pmsignal.h
@@ -41,6 +41,7 @@ typedef enum
PMSIGNAL_BACKGROUND_WORKER_CHANGE, /* background worker state change */
PMSIGNAL_START_WALRECEIVER, /* start a walreceiver */
PMSIGNAL_ADVANCE_STATE_MACHINE, /* advance postmaster's state machine */
+ PMSIGNAL_DEMOTING, /* restart startup process */
NUM_PMSIGNALS /* Must be last value of enum! */
} PMSignalReason;
diff --git a/src/include/storage/procsignal.h b/src/include/storage/procsignal.h
index 5cb39697f3..eb0bda04f5 100644
--- a/src/include/storage/procsignal.h
+++ b/src/include/storage/procsignal.h
@@ -34,6 +34,7 @@ typedef enum
PROCSIG_PARALLEL_MESSAGE, /* message from cooperating parallel backend */
PROCSIG_WALSND_INIT_STOPPING, /* ask walsenders to prepare for shutdown */
PROCSIG_BARRIER, /* global barrier interrupt */
+ PROCSIG_CHECKPOINTER_DEMOTING, /* ask checkpointer to demote */
/* Recovery conflict reasons */
PROCSIG_RECOVERY_CONFLICT_DATABASE,
diff --git a/src/include/utils/pidfile.h b/src/include/utils/pidfile.h
index 63fefe5c4c..f761d2c4ef 100644
--- a/src/include/utils/pidfile.h
+++ b/src/include/utils/pidfile.h
@@ -50,6 +50,7 @@
*/
#define PM_STATUS_STARTING "starting" /* still starting up */
#define PM_STATUS_STOPPING "stopping" /* in shutdown sequence */
+#define PM_STATUS_DEMOTING "demoting" /* demote sequence */
#define PM_STATUS_READY "ready " /* ready for connections */
#define PM_STATUS_STANDBY "standby " /* up, won't accept connections */
--
2.20.1
--MP_/P4ciz=0H9_d2agoKMBTFIxn--
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: Extended Statistics set/restore/clear functions.
@ 2026-01-15 09:33 Michael Paquier <[email protected]>
0 siblings, 0 replies; 3+ messages in thread
From: Michael Paquier @ 2026-01-15 09:33 UTC (permalink / raw)
To: Corey Huinker <[email protected]>; +Cc: Tender Wang <[email protected]>; PostgreSQL Hackers <[email protected]>
On Thu, Jan 15, 2026 at 03:59:27AM -0500, Corey Huinker wrote:
> Correct, that was done in the v7 patchset to conform to 688dc6299a5b.
>
> All four names are available through pg_stats_ext, so the additional
> requirements for pg_dump may not be a an issue. However, I do have some
> vague memory that all four names was a problem in some way beyond just
> giving the parameters more chances to disagree with reality. We'll find out
> soon enough...
I don't see how providing the four arguments would be an incorrect
thing to do. We must do the Rangevar lookup first anyway and ensure
that a lock is taken on the relation before opening the catalog. Or
we would do the opposite of what VACUUM does when updating the stats.
That would also be the opposite of what we do for the relation and
attribute stats.
As you say, these calls will be integrated in pg_dump and pg_upgrade,
but I want these to be right from the start for cases where these
functions are called outside these contexts, like the other
clear/restore functions. Perhaps that could be made lighter, but at
least what I have sent has a safe ordering, and we would rely on a
single path for the table lookup and the ACL checks. The key point to
me is that one cannot drop an extended stats object while we lock the
table, looking at the table OID from the pg_stats_ext catalog leads to
more complicated code. FWIW, I had a lot of fun today testing a lot
of concurrent cases to find out that everything I could think of was
actually unsafe without a proper lock taken first on the table, before
touching the stats, with the lock remaining until the transaction that
calls the function and touches the stats commits, releasing the lock.
--
Michael
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^ permalink raw reply [nested|flat] 3+ messages in thread
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2020-04-10 16:01 [PATCH] Demote PoC Jehan-Guillaume de Rorthais <[email protected]>
2020-04-10 16:01 [PATCH] Demote PoC Jehan-Guillaume de Rorthais <[email protected]>
2026-01-15 09:33 Re: Extended Statistics set/restore/clear functions. Michael Paquier <[email protected]>
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