walreceiverfuncs.c

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/*-------------------------------------------------------------------------
 *
 * walreceiverfuncs.c
 *
 * This file contains functions used by the startup process to communicate
 * with the walreceiver process. Functions implementing walreceiver itself
 * are in walreceiver.c.
 *
 * Portions Copyright (c) 2010-2026, PostgreSQL Global Development Group
 *
 *
 * IDENTIFICATION
 *    src/backend/replication/walreceiverfuncs.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include <sys/stat.h>
#include <sys/time.h>
#include <time.h>
#include <unistd.h>
#include <signal.h>
 
#include "access/xlog_internal.h"
#include "access/xlogrecovery.h"
#include "pgstat.h"
#include "replication/walreceiver.h"
#include "storage/pmsignal.h"
#include "storage/proc.h"
#include "storage/shmem.h"
#include "storage/subsystems.h"
#include "utils/timestamp.h"
#include "utils/wait_event.h"
 
WalRcvData *WalRcv = NULL;
 
static void WalRcvShmemRequest(void *arg);
static void WalRcvShmemInit(void *arg);
 
const ShmemCallbacks WalRcvShmemCallbacks = {
    .request_fn = WalRcvShmemRequest,
    .init_fn = WalRcvShmemInit,
};
 
/*
 * How long to wait for walreceiver to start up after requesting
 * postmaster to launch it. In seconds.
 */
#define WALRCV_STARTUP_TIMEOUT 10
 
/* Register shared memory space needed by walreceiver */
static void
WalRcvShmemRequest(void *arg)
{
    ShmemRequestStruct(.name = "Wal Receiver Ctl",
                       .size = sizeof(WalRcvData),
                       .ptr = (void **) &WalRcv,
        );
}
 
/* Initialize walreceiver-related shared memory */
static void
WalRcvShmemInit(void *arg)
{
    MemSet(WalRcv, 0, sizeof(WalRcvData));
    WalRcv->walRcvState = WALRCV_STOPPED;
    ConditionVariableInit(&WalRcv->walRcvStoppedCV);
    SpinLockInit(&WalRcv->mutex);
    pg_atomic_init_u64(&WalRcv->writtenUpto, 0);
    WalRcv->procno = INVALID_PROC_NUMBER;
}
 
/* Is walreceiver running (or starting up)? */
bool
WalRcvRunning(void)
{
    WalRcvData *walrcv = WalRcv;
    WalRcvState state;
    pg_time_t   startTime;
 
    SpinLockAcquire(&walrcv->mutex);
 
    state = walrcv->walRcvState;
    startTime = walrcv->startTime;
 
    SpinLockRelease(&walrcv->mutex);
 
    /*
     * If it has taken too long for walreceiver to start up, give up. Setting
     * the state to STOPPED ensures that if walreceiver later does start up
     * after all, it will see that it's not supposed to be running and die
     * without doing anything.
     */
    if (state == WALRCV_STARTING)
    {
        pg_time_t   now = (pg_time_t) time(NULL);
 
        if ((now - startTime) > WALRCV_STARTUP_TIMEOUT)
        {
            bool        stopped = false;
 
            SpinLockAcquire(&walrcv->mutex);
            if (walrcv->walRcvState == WALRCV_STARTING)
            {
                state = walrcv->walRcvState = WALRCV_STOPPED;
                stopped = true;
            }
            SpinLockRelease(&walrcv->mutex);
 
            if (stopped)
                ConditionVariableBroadcast(&walrcv->walRcvStoppedCV);
        }
    }
 
    if (state != WALRCV_STOPPED)
        return true;
    else
        return false;
}
 
/* Return the state of the walreceiver. */
WalRcvState
WalRcvGetState(void)
{
    WalRcvData *walrcv = WalRcv;
    WalRcvState state;
 
    SpinLockAcquire(&walrcv->mutex);
    state = walrcv->walRcvState;
    SpinLockRelease(&walrcv->mutex);
 
    return state;
}
 
/*
 * Is walreceiver running and streaming (or at least attempting to connect,
 * or starting up)?
 */
bool
WalRcvStreaming(void)
{
    WalRcvData *walrcv = WalRcv;
    WalRcvState state;
    pg_time_t   startTime;
 
    SpinLockAcquire(&walrcv->mutex);
 
    state = walrcv->walRcvState;
    startTime = walrcv->startTime;
 
    SpinLockRelease(&walrcv->mutex);
 
    /*
     * If it has taken too long for walreceiver to start up, give up. Setting
     * the state to STOPPED ensures that if walreceiver later does start up
     * after all, it will see that it's not supposed to be running and die
     * without doing anything.
     */
    if (state == WALRCV_STARTING)
    {
        pg_time_t   now = (pg_time_t) time(NULL);
 
        if ((now - startTime) > WALRCV_STARTUP_TIMEOUT)
        {
            bool        stopped = false;
 
            SpinLockAcquire(&walrcv->mutex);
            if (walrcv->walRcvState == WALRCV_STARTING)
            {
                state = walrcv->walRcvState = WALRCV_STOPPED;
                stopped = true;
            }
            SpinLockRelease(&walrcv->mutex);
 
            if (stopped)
                ConditionVariableBroadcast(&walrcv->walRcvStoppedCV);
        }
    }
 
    if (state == WALRCV_STREAMING || state == WALRCV_STARTING ||
        state == WALRCV_CONNECTING || state == WALRCV_RESTARTING)
        return true;
    else
        return false;
}
 
/*
 * Stop walreceiver (if running) and wait for it to die.
 * Executed by the Startup process.
 */
void
ShutdownWalRcv(void)
{
    WalRcvData *walrcv = WalRcv;
    pid_t       walrcvpid = 0;
    bool        stopped = false;
 
    /*
     * Request walreceiver to stop. Walreceiver will switch to WALRCV_STOPPED
     * mode once it's finished, and will also request postmaster to not
     * restart itself.
     */
    SpinLockAcquire(&walrcv->mutex);
    switch (walrcv->walRcvState)
    {
        case WALRCV_STOPPED:
            break;
        case WALRCV_STARTING:
            walrcv->walRcvState = WALRCV_STOPPED;
            stopped = true;
            break;
 
        case WALRCV_CONNECTING:
        case WALRCV_STREAMING:
        case WALRCV_WAITING:
        case WALRCV_RESTARTING:
            walrcv->walRcvState = WALRCV_STOPPING;
            pg_fallthrough;
        case WALRCV_STOPPING:
            walrcvpid = walrcv->pid;
            break;
    }
    SpinLockRelease(&walrcv->mutex);
 
    /* Unnecessary but consistent. */
    if (stopped)
        ConditionVariableBroadcast(&walrcv->walRcvStoppedCV);
 
    /*
     * Signal walreceiver process if it was still running.
     */
    if (walrcvpid != 0)
        kill(walrcvpid, SIGTERM);
 
    /*
     * Wait for walreceiver to acknowledge its death by setting state to
     * WALRCV_STOPPED.
     */
    ConditionVariablePrepareToSleep(&walrcv->walRcvStoppedCV);
    while (WalRcvRunning())
        ConditionVariableSleep(&walrcv->walRcvStoppedCV,
                               WAIT_EVENT_WAL_RECEIVER_EXIT);
    ConditionVariableCancelSleep();
}
 
/*
 * Request postmaster to start walreceiver.
 *
 * "recptr" indicates the position where streaming should begin.  "conninfo"
 * is a libpq connection string to use.  "slotname" is, optionally, the name
 * of a replication slot to acquire.  "create_temp_slot" indicates to create
 * a temporary slot when no "slotname" is given.
 *
 * WAL receivers do not directly load GUC parameters used for the connection
 * to the primary, and rely on the values passed down by the caller of this
 * routine instead.  Hence, the addition of any new parameters should happen
 * through this code path.
 */
void
RequestXLogStreaming(TimeLineID tli, XLogRecPtr recptr, const char *conninfo,
                     const char *slotname, bool create_temp_slot)
{
    WalRcvData *walrcv = WalRcv;
    bool        launch = false;
    pg_time_t   now = (pg_time_t) time(NULL);
    ProcNumber  walrcv_proc;
 
    /*
     * We always start at the beginning of the segment. That prevents a broken
     * segment (i.e., with no records in the first half of a segment) from
     * being created by XLOG streaming, which might cause trouble later on if
     * the segment is e.g archived.
     */
    if (XLogSegmentOffset(recptr, wal_segment_size) != 0)
        recptr -= XLogSegmentOffset(recptr, wal_segment_size);
 
    SpinLockAcquire(&walrcv->mutex);
 
    /* It better be stopped if we try to restart it */
    Assert(walrcv->walRcvState == WALRCV_STOPPED ||
           walrcv->walRcvState == WALRCV_WAITING);
 
    /*
     * Use configured replication slot if present, and ignore the value of
     * create_temp_slot as the slot name should be persistent.  Otherwise, use
     * create_temp_slot to determine whether this WAL receiver should create a
     * temporary slot by itself and use it, or not.
     */
    if (slotname != NULL && slotname[0] != '\0')
    {
        strlcpy(walrcv->slotname, slotname, NAMEDATALEN);
        walrcv->is_temp_slot = false;
    }
    else
    {
        walrcv->slotname[0] = '\0';
        walrcv->is_temp_slot = create_temp_slot;
    }
 
    /*
     * While waiting for instructions, the WAL receiver uses the same
     * connection, so do not clobber the user-visible conninfo already saved.
     */
    if (walrcv->walRcvState == WALRCV_STOPPED)
    {
        launch = true;
        walrcv->walRcvState = WALRCV_STARTING;
 
        if (conninfo != NULL)
            strlcpy(walrcv->conninfo, conninfo, MAXCONNINFO);
        else
            walrcv->conninfo[0] = '\0';
    }
    else
        walrcv->walRcvState = WALRCV_RESTARTING;
    walrcv->startTime = now;
 
    /*
     * If this is the first startup of walreceiver (on this timeline),
     * initialize flushedUpto and latestChunkStart to the starting point.
     */
    if (!XLogRecPtrIsValid(walrcv->receiveStart) || walrcv->receivedTLI != tli)
    {
        walrcv->flushedUpto = recptr;
        walrcv->receivedTLI = tli;
        walrcv->latestChunkStart = recptr;
 
        /*
         * Pairs with pg_atomic_read_membarrier_u64() in
         * GetWalRcvWriteRecPtr().
         */
        pg_atomic_write_membarrier_u64(&walrcv->writtenUpto, recptr);
    }
    walrcv->receiveStart = recptr;
    walrcv->receiveStartTLI = tli;
 
    walrcv_proc = walrcv->procno;
 
    SpinLockRelease(&walrcv->mutex);
 
    if (launch)
        SendPostmasterSignal(PMSIGNAL_START_WALRECEIVER);
    else if (walrcv_proc != INVALID_PROC_NUMBER)
        SetLatch(&GetPGProcByNumber(walrcv_proc)->procLatch);
}
 
/*
 * Returns the last+1 byte position that walreceiver has flushed.
 *
 * Optionally, returns the previous chunk start, that is the first byte
 * written in the most recent walreceiver flush cycle.  Callers not
 * interested in that value may pass NULL for latestChunkStart. Same for
 * receiveTLI.
 */
XLogRecPtr
GetWalRcvFlushRecPtr(XLogRecPtr *latestChunkStart, TimeLineID *receiveTLI)
{
    WalRcvData *walrcv = WalRcv;
    XLogRecPtr  recptr;
 
    SpinLockAcquire(&walrcv->mutex);
    recptr = walrcv->flushedUpto;
    if (latestChunkStart)
        *latestChunkStart = walrcv->latestChunkStart;
    if (receiveTLI)
        *receiveTLI = walrcv->receivedTLI;
    SpinLockRelease(&walrcv->mutex);
 
    return recptr;
}
 
/*
 * Returns the last+1 byte position that walreceiver has written.
 *
 * Use pg_atomic_read_membarrier_u64() to ensure that callers see up-to-date
 * shared memory state, matching the barrier semantics provided by the
 * spinlock in GetWalRcvFlushRecPtr() and other LSN-position functions.
 */
XLogRecPtr
GetWalRcvWriteRecPtr(void)
{
    WalRcvData *walrcv = WalRcv;
 
    return pg_atomic_read_membarrier_u64(&walrcv->writtenUpto);
}
 
/*
 * Returns the replication apply delay in ms or -1
 * if the apply delay info is not available
 */
int
GetReplicationApplyDelay(void)
{
    WalRcvData *walrcv = WalRcv;
    XLogRecPtr  receivePtr;
    XLogRecPtr  replayPtr;
    TimestampTz chunkReplayStartTime;
 
    SpinLockAcquire(&walrcv->mutex);
    receivePtr = walrcv->flushedUpto;
    SpinLockRelease(&walrcv->mutex);
 
    replayPtr = GetXLogReplayRecPtr(NULL);
 
    if (receivePtr == replayPtr)
        return 0;
 
    chunkReplayStartTime = GetCurrentChunkReplayStartTime();
 
    if (chunkReplayStartTime == 0)
        return -1;
 
    return TimestampDifferenceMilliseconds(chunkReplayStartTime,
                                           GetCurrentTimestamp());
}
 
/*
 * Returns the network latency in ms, note that this includes any
 * difference in clock settings between the servers, as well as timezone.
 */
int
GetReplicationTransferLatency(void)
{
    WalRcvData *walrcv = WalRcv;
    TimestampTz lastMsgSendTime;
    TimestampTz lastMsgReceiptTime;
 
    SpinLockAcquire(&walrcv->mutex);
    lastMsgSendTime = walrcv->lastMsgSendTime;
    lastMsgReceiptTime = walrcv->lastMsgReceiptTime;
    SpinLockRelease(&walrcv->mutex);
 
    return TimestampDifferenceMilliseconds(lastMsgSendTime,
                                           lastMsgReceiptTime);
}