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Revert: Implement pg_wal_replay_wait() stored procedure

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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
This commit is contained in:
Alexander Korotkov
2024-04-11 16:30:32 +03:00
parent 922c4c461d
commit 772faafca1
20 changed files with 4 additions and 694 deletions
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3
src/backend/commands/Makefile
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@@ -61,7 +61,6 @@ OBJS = \
vacuum.o \
vacuumparallel.o \
variable.o \
view.o \
waitlsn.o
view.o
include $(top_srcdir)/src/backend/common.mk

1
src/backend/commands/meson.build
View File

@@ -50,5 +50,4 @@ backend_sources += files(
'vacuumparallel.c',
'variable.c',
'view.c',
'waitlsn.c',
)

337
src/backend/commands/waitlsn.c
View File

@@ -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();
}