Adding upstream version 14.5.upstream/14.5upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 351 insertions, 0 deletions

diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
new file mode 100644
index 0000000..715d519
--- /dev/null
+++ b/src/backend/postmaster/bgwriter.c
@@ -0,0 +1,351 @@
+/*-------------------------------------------------------------------------
+ *
+ * bgwriter.c
+ *
+ * The background writer (bgwriter) is new as of Postgres 8.0.  It attempts
+ * to keep regular backends from having to write out dirty shared buffers
+ * (which they would only do when needing to free a shared buffer to read in
+ * another page).  In the best scenario all writes from shared buffers will
+ * be issued by the background writer process.  However, regular backends are
+ * still empowered to issue writes if the bgwriter fails to maintain enough
+ * clean shared buffers.
+ *
+ * As of Postgres 9.2 the bgwriter no longer handles checkpoints.
+ *
+ * The bgwriter is started by the postmaster as soon as the startup subprocess
+ * finishes, or as soon as recovery begins if we are doing archive recovery.
+ * It remains alive until the postmaster commands it to terminate.
+ * Normal termination is by SIGTERM, which instructs the bgwriter to exit(0).
+ * Emergency termination is by SIGQUIT; like any backend, the bgwriter will
+ * simply abort and exit on SIGQUIT.
+ *
+ * If the bgwriter exits unexpectedly, the postmaster treats that the same
+ * as a backend crash: shared memory may be corrupted, so remaining backends
+ * should be killed by SIGQUIT and then a recovery cycle started.
+ *
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/postmaster/bgwriter.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/xlog.h"
+#include "access/xlog_internal.h"
+#include "libpq/pqsignal.h"
+#include "miscadmin.h"
+#include "pgstat.h"
+#include "postmaster/bgwriter.h"
+#include "postmaster/interrupt.h"
+#include "storage/buf_internals.h"
+#include "storage/bufmgr.h"
+#include "storage/condition_variable.h"
+#include "storage/fd.h"
+#include "storage/ipc.h"
+#include "storage/lwlock.h"
+#include "storage/proc.h"
+#include "storage/procsignal.h"
+#include "storage/shmem.h"
+#include "storage/smgr.h"
+#include "storage/spin.h"
+#include "storage/standby.h"
+#include "utils/guc.h"
+#include "utils/memutils.h"
+#include "utils/resowner.h"
+#include "utils/timestamp.h"
+
+/*
+ * GUC parameters
+ */
+int			BgWriterDelay = 200;
+
+/*
+ * Multiplier to apply to BgWriterDelay when we decide to hibernate.
+ * (Perhaps this needs to be configurable?)
+ */
+#define HIBERNATE_FACTOR			50
+
+/*
+ * Interval in which standby snapshots are logged into the WAL stream, in
+ * milliseconds.
+ */
+#define LOG_SNAPSHOT_INTERVAL_MS 15000
+
+/*
+ * LSN and timestamp at which we last issued a LogStandbySnapshot(), to avoid
+ * doing so too often or repeatedly if there has been no other write activity
+ * in the system.
+ */
+static TimestampTz last_snapshot_ts;
+static XLogRecPtr last_snapshot_lsn = InvalidXLogRecPtr;
+
+
+/*
+ * Main entry point for bgwriter process
+ *
+ * This is invoked from AuxiliaryProcessMain, which has already created the
+ * basic execution environment, but not enabled signals yet.
+ */
+void
+BackgroundWriterMain(void)
+{
+	sigjmp_buf	local_sigjmp_buf;
+	MemoryContext bgwriter_context;
+	bool		prev_hibernate;
+	WritebackContext wb_context;
+
+	/*
+	 * Properly accept or ignore signals that might be sent to us.
+	 */
+	pqsignal(SIGHUP, SignalHandlerForConfigReload);
+	pqsignal(SIGINT, SIG_IGN);
+	pqsignal(SIGTERM, SignalHandlerForShutdownRequest);
+	/* SIGQUIT handler was already set up by InitPostmasterChild */
+	pqsignal(SIGALRM, SIG_IGN);
+	pqsignal(SIGPIPE, SIG_IGN);
+	pqsignal(SIGUSR1, procsignal_sigusr1_handler);
+	pqsignal(SIGUSR2, SIG_IGN);
+
+	/*
+	 * Reset some signals that are accepted by postmaster but not here
+	 */
+	pqsignal(SIGCHLD, SIG_DFL);
+
+	/*
+	 * We just started, assume there has been either a shutdown or
+	 * end-of-recovery snapshot.
+	 */
+	last_snapshot_ts = GetCurrentTimestamp();
+
+	/*
+	 * 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.  Formerly this code just ran in
+	 * TopMemoryContext, but resetting that would be a really bad idea.
+	 */
+	bgwriter_context = AllocSetContextCreate(TopMemoryContext,
+											 "Background Writer",
+											 ALLOCSET_DEFAULT_SIZES);
+	MemoryContextSwitchTo(bgwriter_context);
+
+	WritebackContextInit(&wb_context, &bgwriter_flush_after);
+
+	/*
+	 * If an exception is encountered, processing resumes here.
+	 *
+	 * 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 the prevailing signal mask
+	 * (to wit, BlockSig) will be restored when longjmp'ing to here.  Thus,
+	 * signals other than SIGQUIT will be blocked until we complete error
+	 * recovery.  It might seem that this policy makes the HOLD_INTERRUPTS()
+	 * call redundant, but it is not since InterruptPending might be set
+	 * already.
+	 */
+	if (sigsetjmp(local_sigjmp_buf, 1) != 0)
+	{
+		/* Since not using PG_TRY, must reset error stack by hand */
+		error_context_stack = NULL;
+
+		/* Prevent interrupts while cleaning up */
+		HOLD_INTERRUPTS();
+
+		/* Report the error to the server log */
+		EmitErrorReport();
+
+		/*
+		 * These operations are really just a minimal subset of
+		 * AbortTransaction().  We don't have very many resources to worry
+		 * about in bgwriter, but we do have LWLocks, buffers, and temp files.
+		 */
+		LWLockReleaseAll();
+		ConditionVariableCancelSleep();
+		AbortBufferIO();
+		UnlockBuffers();
+		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.
+		 */
+		MemoryContextSwitchTo(bgwriter_context);
+		FlushErrorState();
+
+		/* Flush any leaked data in the top-level context */
+		MemoryContextResetAndDeleteChildren(bgwriter_context);
+
+		/* re-initialize to avoid repeated errors causing problems */
+		WritebackContextInit(&wb_context, &bgwriter_flush_after);
+
+		/* Now we can allow interrupts again */
+		RESUME_INTERRUPTS();
+
+		/*
+		 * Sleep at least 1 second after any error.  A write error is likely
+		 * to be repeated, and we don't want to be filling the error logs as
+		 * fast as we can.
+		 */
+		pg_usleep(1000000L);
+
+		/*
+		 * Close all open files after any error.  This is helpful on Windows,
+		 * where holding deleted files open causes various strange errors.
+		 * It's not clear we need it elsewhere, but shouldn't hurt.
+		 */
+		smgrcloseall();
+
+		/* Report wait end here, when there is no further possibility of wait */
+		pgstat_report_wait_end();
+	}
+
+	/* We can now handle ereport(ERROR) */
+	PG_exception_stack = &local_sigjmp_buf;
+
+	/*
+	 * Unblock signals (they were blocked when the postmaster forked us)
+	 */
+	PG_SETMASK(&UnBlockSig);
+
+	/*
+	 * Reset hibernation state after any error.
+	 */
+	prev_hibernate = false;
+
+	/*
+	 * Loop forever
+	 */
+	for (;;)
+	{
+		bool		can_hibernate;
+		int			rc;
+
+		/* Clear any already-pending wakeups */
+		ResetLatch(MyLatch);
+
+		HandleMainLoopInterrupts();
+
+		/*
+		 * Do one cycle of dirty-buffer writing.
+		 */
+		can_hibernate = BgBufferSync(&wb_context);
+
+		/*
+		 * Send off activity statistics to the stats collector
+		 */
+		pgstat_send_bgwriter();
+
+		if (FirstCallSinceLastCheckpoint())
+		{
+			/*
+			 * After any checkpoint, close all smgr files.  This is so we
+			 * won't hang onto smgr references to deleted files indefinitely.
+			 */
+			smgrcloseall();
+		}
+
+		/*
+		 * Log a new xl_running_xacts every now and then so replication can
+		 * get into a consistent state faster (think of suboverflowed
+		 * snapshots) and clean up resources (locks, KnownXids*) more
+		 * frequently. The costs of this are relatively low, so doing it 4
+		 * times (LOG_SNAPSHOT_INTERVAL_MS) a minute seems fine.
+		 *
+		 * We assume the interval for writing xl_running_xacts is
+		 * significantly bigger than BgWriterDelay, so we don't complicate the
+		 * overall timeout handling but just assume we're going to get called
+		 * often enough even if hibernation mode is active. It's not that
+		 * important that LOG_SNAPSHOT_INTERVAL_MS is met strictly. To make
+		 * sure we're not waking the disk up unnecessarily on an idle system
+		 * we check whether there has been any WAL inserted since the last
+		 * time we've logged a running xacts.
+		 *
+		 * We do this logging in the bgwriter as it is the only process that
+		 * is run regularly and returns to its mainloop all the time. E.g.
+		 * Checkpointer, when active, is barely ever in its mainloop and thus
+		 * makes it hard to log regularly.
+		 */
+		if (XLogStandbyInfoActive() && !RecoveryInProgress())
+		{
+			TimestampTz timeout = 0;
+			TimestampTz now = GetCurrentTimestamp();
+
+			timeout = TimestampTzPlusMilliseconds(last_snapshot_ts,
+												  LOG_SNAPSHOT_INTERVAL_MS);
+
+			/*
+			 * Only log if enough time has passed and interesting records have
+			 * been inserted since the last snapshot.  Have to compare with <=
+			 * instead of < because GetLastImportantRecPtr() points at the
+			 * start of a record, whereas last_snapshot_lsn points just past
+			 * the end of the record.
+			 */
+			if (now >= timeout &&
+				last_snapshot_lsn <= GetLastImportantRecPtr())
+			{
+				last_snapshot_lsn = LogStandbySnapshot();
+				last_snapshot_ts = now;
+			}
+		}
+
+		/*
+		 * Sleep until we are signaled or BgWriterDelay has elapsed.
+		 *
+		 * Note: the feedback control loop in BgBufferSync() expects that we
+		 * will call it every BgWriterDelay msec.  While it's not critical for
+		 * correctness that that be exact, the feedback loop might misbehave
+		 * if we stray too far from that.  Hence, avoid loading this process
+		 * down with latch events that are likely to happen frequently during
+		 * normal operation.
+		 */
+		rc = WaitLatch(MyLatch,
+					   WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
+					   BgWriterDelay /* ms */ , WAIT_EVENT_BGWRITER_MAIN);
+
+		/*
+		 * If no latch event and BgBufferSync says nothing's happening, extend
+		 * the sleep in "hibernation" mode, where we sleep for much longer
+		 * than bgwriter_delay says.  Fewer wakeups save electricity.  When a
+		 * backend starts using buffers again, it will wake us up by setting
+		 * our latch.  Because the extra sleep will persist only as long as no
+		 * buffer allocations happen, this should not distort the behavior of
+		 * BgBufferSync's control loop too badly; essentially, it will think
+		 * that the system-wide idle interval didn't exist.
+		 *
+		 * There is a race condition here, in that a backend might allocate a
+		 * buffer between the time BgBufferSync saw the alloc count as zero
+		 * and the time we call StrategyNotifyBgWriter.  While it's not
+		 * critical that we not hibernate anyway, we try to reduce the odds of
+		 * that by only hibernating when BgBufferSync says nothing's happening
+		 * for two consecutive cycles.  Also, we mitigate any possible
+		 * consequences of a missed wakeup by not hibernating forever.
+		 */
+		if (rc == WL_TIMEOUT && can_hibernate && prev_hibernate)
+		{
+			/* Ask for notification at next buffer allocation */
+			StrategyNotifyBgWriter(MyProc->pgprocno);
+			/* Sleep ... */
+			(void) WaitLatch(MyLatch,
+							 WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
+							 BgWriterDelay * HIBERNATE_FACTOR,
+							 WAIT_EVENT_BGWRITER_HIBERNATE);
+			/* Reset the notification request in case we timed out */
+			StrategyNotifyBgWriter(-1);
+		}
+
+		prev_hibernate = can_hibernate;
+	}
+}