Revert: Implement pg_wal_replay_wait() stored procedure

This commit reverts 06c418e163, e37662f221, bf1e650806, 25f42429e2,
ee79928441, and 74eaf66f98 per review by Heikki Linnakangas.

Discussion: https://postgr.es/m/b155606b-e744-4218-bda5-29379779da1a%40iki.fi

3 files changed, 1 insertions, 340 deletions

diff --git a/src/backend/commands/Makefile b/src/backend/commands/Makefile
index cede90c3b98..48f7348f91c 100644
--- a/src/backend/commands/Makefile
+++ b/src/backend/commands/Makefile
@@ -61,7 +61,6 @@ OBJS = \
 	vacuum.o \
 	vacuumparallel.o \
 	variable.o \
-	view.o \
-	waitlsn.o
+	view.o
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/commands/meson.build b/src/backend/commands/meson.build
index 7549be5dc3b..6dd00a4abde 100644
--- a/src/backend/commands/meson.build
+++ b/src/backend/commands/meson.build
@@ -50,5 +50,4 @@ backend_sources += files(
   'vacuumparallel.c',
   'variable.c',
   'view.c',
-  'waitlsn.c',
 )
diff --git a/src/backend/commands/waitlsn.c b/src/backend/commands/waitlsn.c
deleted file mode 100644
index 1a83c34e09f..00000000000
--- a/src/backend/commands/waitlsn.c
+++ /dev/null
@@ -1,337 +0,0 @@
-/*-------------------------------------------------------------------------
- *
- * waitlsn.c
- *	  Implements waiting for the given replay LSN, which is used in
- *	  CALL pg_wal_replay_wait(target_lsn pg_lsn, timeout float8).
- *
- * Copyright (c) 2024, PostgreSQL Global Development Group
- *
- * IDENTIFICATION
- *	  src/backend/commands/waitlsn.c
- *
- *-------------------------------------------------------------------------
- */
-
-#include "postgres.h"
-
-#include <float.h>
-#include <math.h>
-
-#include "pgstat.h"
-#include "access/xlog.h"
-#include "access/xlogrecovery.h"
-#include "commands/waitlsn.h"
-#include "funcapi.h"
-#include "miscadmin.h"
-#include "storage/latch.h"
-#include "storage/proc.h"
-#include "storage/shmem.h"
-#include "utils/fmgrprotos.h"
-#include "utils/pg_lsn.h"
-#include "utils/snapmgr.h"
-#include "utils/wait_event_types.h"
-
-static int	lsn_cmp(const pairingheap_node *a, const pairingheap_node *b,
-					void *arg);
-
-struct WaitLSNState *waitLSN = NULL;
-
-/* Report the amount of shared memory space needed for WaitLSNState. */
-Size
-WaitLSNShmemSize(void)
-{
-	Size		size;
-
-	size = offsetof(WaitLSNState, procInfos);
-	size = add_size(size, mul_size(MaxBackends, sizeof(WaitLSNProcInfo)));
-	return size;
-}
-
-/* Initialize the WaitLSNState in the shared memory. */
-void
-WaitLSNShmemInit(void)
-{
-	bool		found;
-
-	waitLSN = (WaitLSNState *) ShmemInitStruct("WaitLSNState",
-											   WaitLSNShmemSize(),
-											   &found);
-	if (!found)
-	{
-		pg_atomic_init_u64(&waitLSN->minWaitedLSN, PG_UINT64_MAX);
-		pairingheap_initialize(&waitLSN->waitersHeap, lsn_cmp, NULL);
-		memset(&waitLSN->procInfos, 0, MaxBackends * sizeof(WaitLSNProcInfo));
-	}
-}
-
-/*
- * Comparison function for waitLSN->waitersHeap heap.  Waiting processes are
- * ordered by lsn, so that the waiter with smallest lsn is at the top.
- */
-static int
-lsn_cmp(const pairingheap_node *a, const pairingheap_node *b, void *arg)
-{
-	const WaitLSNProcInfo *aproc = pairingheap_const_container(WaitLSNProcInfo, phNode, a);
-	const WaitLSNProcInfo *bproc = pairingheap_const_container(WaitLSNProcInfo, phNode, b);
-
-	if (aproc->waitLSN < bproc->waitLSN)
-		return 1;
-	else if (aproc->waitLSN > bproc->waitLSN)
-		return -1;
-	else
-		return 0;
-}
-
-/*
- * Update waitLSN->minWaitedLSN according to the current state of
- * waitLSN->waitersHeap.
- */
-static void
-updateMinWaitedLSN(void)
-{
-	XLogRecPtr	minWaitedLSN = PG_UINT64_MAX;
-
-	if (!pairingheap_is_empty(&waitLSN->waitersHeap))
-	{
-		pairingheap_node *node = pairingheap_first(&waitLSN->waitersHeap);
-
-		minWaitedLSN = pairingheap_container(WaitLSNProcInfo, phNode, node)->waitLSN;
-	}
-
-	pg_atomic_write_u64(&waitLSN->minWaitedLSN, minWaitedLSN);
-}
-
-/*
- * Put the current process into the heap of LSN waiters.
- */
-static void
-addLSNWaiter(XLogRecPtr lsn)
-{
-	WaitLSNProcInfo *procInfo = &waitLSN->procInfos[MyProcNumber];
-
-	LWLockAcquire(WaitLSNLock, LW_EXCLUSIVE);
-
-	Assert(!procInfo->inHeap);
-
-	procInfo->procnum = MyProcNumber;
-	procInfo->waitLSN = lsn;
-
-	pairingheap_add(&waitLSN->waitersHeap, &procInfo->phNode);
-	procInfo->inHeap = true;
-	updateMinWaitedLSN();
-
-	LWLockRelease(WaitLSNLock);
-}
-
-/*
- * Remove the current process from the heap of LSN waiters if it's there.
- */
-static void
-deleteLSNWaiter(void)
-{
-	WaitLSNProcInfo *procInfo = &waitLSN->procInfos[MyProcNumber];
-
-	LWLockAcquire(WaitLSNLock, LW_EXCLUSIVE);
-
-	if (!procInfo->inHeap)
-	{
-		LWLockRelease(WaitLSNLock);
-		return;
-	}
-
-	pairingheap_remove(&waitLSN->waitersHeap, &procInfo->phNode);
-	procInfo->inHeap = false;
-	updateMinWaitedLSN();
-
-	LWLockRelease(WaitLSNLock);
-}
-
-/*
- * Set latches of LSN waiters whose LSN has been replayed.  Set latches of all
- * LSN waiters when InvalidXLogRecPtr is given.
- */
-void
-WaitLSNSetLatches(XLogRecPtr currentLSN)
-{
-	int			i;
-	int		   *wakeUpProcNums;
-	int			numWakeUpProcs = 0;
-
-	wakeUpProcNums = palloc(sizeof(int) * MaxBackends);
-
-	LWLockAcquire(WaitLSNLock, LW_EXCLUSIVE);
-
-	/*
-	 * Iterate the pairing heap of waiting processes till we find LSN not yet
-	 * replayed.  Record the process numbers to set their latches later.
-	 */
-	while (!pairingheap_is_empty(&waitLSN->waitersHeap))
-	{
-		pairingheap_node *node = pairingheap_first(&waitLSN->waitersHeap);
-		WaitLSNProcInfo *procInfo = pairingheap_container(WaitLSNProcInfo, phNode, node);
-
-		if (!XLogRecPtrIsInvalid(currentLSN) &&
-			procInfo->waitLSN > currentLSN)
-			break;
-
-		wakeUpProcNums[numWakeUpProcs++] = procInfo->procnum;
-		(void) pairingheap_remove_first(&waitLSN->waitersHeap);
-		procInfo->inHeap = false;
-	}
-
-	updateMinWaitedLSN();
-
-	LWLockRelease(WaitLSNLock);
-
-	/*
-	 * Set latches for processes, whose waited LSNs are already replayed. This
-	 * involves spinlocks.  So, we shouldn't do this under a spinlock.
-	 */
-	for (i = 0; i < numWakeUpProcs; i++)
-	{
-		PGPROC	   *backend;
-
-		backend = GetPGProcByNumber(wakeUpProcNums[i]);
-		SetLatch(&backend->procLatch);
-	}
-	pfree(wakeUpProcNums);
-}
-
-/*
- * Delete our item from shmem array if any.
- */
-void
-WaitLSNCleanup(void)
-{
-	/*
-	 * We do a fast-path check of the 'inHeap' flag without the lock.  This
-	 * flag is set to true only by the process itself.  So, it's only possible
-	 * to get a false positive.  But that will be eliminated by a recheck
-	 * inside deleteLSNWaiter().
-	 */
-	if (waitLSN->procInfos[MyProcNumber].inHeap)
-		deleteLSNWaiter();
-}
-
-/*
- * Wait using MyLatch till the given LSN is replayed, the postmaster dies or
- * timeout happens.
- */
-void
-WaitForLSN(XLogRecPtr targetLSN, int64 timeout)
-{
-	XLogRecPtr	currentLSN;
-	TimestampTz endtime = 0;
-
-	/* Shouldn't be called when shmem isn't initialized */
-	Assert(waitLSN);
-
-	/* Should be only called by a backend */
-	Assert(MyBackendType == B_BACKEND && MyProcNumber <= MaxBackends);
-
-	if (!RecoveryInProgress())
-		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("recovery is not in progress"),
-				 errhint("Waiting for LSN can only be executed during recovery.")));
-
-	/* If target LSN is already replayed, exit immediately */
-	if (targetLSN <= GetXLogReplayRecPtr(NULL))
-		return;
-
-	if (timeout > 0)
-		endtime = TimestampTzPlusMilliseconds(GetCurrentTimestamp(), timeout);
-
-	addLSNWaiter(targetLSN);
-
-	for (;;)
-	{
-		int			rc;
-		int			latch_events = WL_LATCH_SET | WL_EXIT_ON_PM_DEATH;
-		long		delay_ms = 0;
-
-		/* Check if the waited LSN has been replayed */
-		currentLSN = GetXLogReplayRecPtr(NULL);
-		if (targetLSN <= currentLSN)
-			break;
-
-		/* Recheck that recovery is still in-progress */
-		if (!RecoveryInProgress())
-			ereport(ERROR,
-					(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-					 errmsg("recovery is not in progress"),
-					 errdetail("Recovery ended before replaying the target LSN %X/%X; last replay LSN %X/%X.",
-							   LSN_FORMAT_ARGS(targetLSN),
-							   LSN_FORMAT_ARGS(currentLSN))));
-
-		if (timeout > 0)
-		{
-			delay_ms = (endtime - GetCurrentTimestamp()) / 1000;
-			latch_events |= WL_TIMEOUT;
-			if (delay_ms <= 0)
-				break;
-		}
-
-		CHECK_FOR_INTERRUPTS();
-
-		rc = WaitLatch(MyLatch, latch_events, delay_ms,
-					   WAIT_EVENT_WAIT_FOR_WAL_REPLAY);
-
-		if (rc & WL_LATCH_SET)
-			ResetLatch(MyLatch);
-	}
-
-	if (targetLSN > currentLSN)
-	{
-		deleteLSNWaiter();
-		ereport(ERROR,
-				(errcode(ERRCODE_QUERY_CANCELED),
-				 errmsg("timed out while waiting for target LSN %X/%X to be replayed; current replay LSN %X/%X",
-						LSN_FORMAT_ARGS(targetLSN),
-						LSN_FORMAT_ARGS(currentLSN))));
-	}
-}
-
-Datum
-pg_wal_replay_wait(PG_FUNCTION_ARGS)
-{
-	XLogRecPtr	target_lsn = PG_GETARG_LSN(0);
-	int64		timeout = PG_GETARG_INT64(1);
-	CallContext *context = (CallContext *) fcinfo->context;
-
-	if (timeout < 0)
-		ereport(ERROR,
-				(errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
-				 errmsg("\"timeout\" must not be negative")));
-
-	/*
-	 * We are going to wait for the LSN replay.  We should first care that we
-	 * don't hold a snapshot and correspondingly our MyProc->xmin is invalid.
-	 * Otherwise, our snapshot could prevent the replay of WAL records
-	 * implying a kind of self-deadlock.  This is the reason why
-	 * pg_wal_replay_wait() is a procedure, not a function.
-	 *
-	 * At first, we check that pg_wal_replay_wait() is called in a non-atomic
-	 * context.  That is, a procedure call isn't wrapped into a transaction,
-	 * another procedure call, or a function call.
-	 *
-	 * Secondly, according to PlannedStmtRequiresSnapshot(), even in an atomic
-	 * context, CallStmt is processed with a snapshot.  Thankfully, we can pop
-	 * this snapshot, because PortalRunUtility() can tolerate this.
-	 */
-	if (context->atomic)
-		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("pg_wal_replay_wait() must be only called in non-atomic context"),
-				 errdetail("Make sure pg_wal_replay_wait() isn't called within a transaction, another procedure, or a function.")));
-
-	if (ActiveSnapshotSet())
-		PopActiveSnapshot();
-	Assert(!ActiveSnapshotSet());
-	InvalidateCatalogSnapshot();
-	Assert(MyProc->xmin == InvalidTransactionId);
-
-	(void) WaitForLSN(target_lsn, timeout);
-
-	PG_RETURN_VOID();
-}