auxprocess.c

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/*-------------------------------------------------------------------------
 * auxprocess.c
 *    functions related to auxiliary processes.
 *
 *
 * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/backend/postmaster/auxprocess.c
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include <unistd.h>
#include <signal.h>
 
#include "libpq/pqsignal.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "postmaster/auxprocess.h"
#include "postmaster/bgwriter.h"
#include "postmaster/startup.h"
#include "postmaster/walwriter.h"
#include "replication/walreceiver.h"
#include "storage/bufmgr.h"
#include "storage/bufpage.h"
#include "storage/condition_variable.h"
#include "storage/ipc.h"
#include "storage/proc.h"
#include "tcop/tcopprot.h"
#include "utils/memutils.h"
#include "utils/ps_status.h"
#include "utils/rel.h"
 
 
static void ShutdownAuxiliaryProcess(int code, Datum arg);
 
 
/* ----------------
 *      global variables
 * ----------------
 */
 
AuxProcType MyAuxProcType = NotAnAuxProcess;    /* declared in miscadmin.h */
 
 
/*
 *   AuxiliaryProcessMain
 *
 *   The main entry point for auxiliary processes, such as the bgwriter,
 *   walwriter, walreceiver, bootstrapper and the shared memory checker code.
 *
 *   This code is here just because of historical reasons.
 */
void
AuxiliaryProcessMain(AuxProcType auxtype)
{
    Assert(IsUnderPostmaster);
 
    MyAuxProcType = auxtype;
 
    switch (MyAuxProcType)
    {
        case StartupProcess:
            MyBackendType = B_STARTUP;
            break;
        case ArchiverProcess:
            MyBackendType = B_ARCHIVER;
            break;
        case BgWriterProcess:
            MyBackendType = B_BG_WRITER;
            break;
        case CheckpointerProcess:
            MyBackendType = B_CHECKPOINTER;
            break;
        case WalWriterProcess:
            MyBackendType = B_WAL_WRITER;
            break;
        case WalReceiverProcess:
            MyBackendType = B_WAL_RECEIVER;
            break;
        default:
            elog(PANIC, "unrecognized process type: %d", (int) MyAuxProcType);
            MyBackendType = B_INVALID;
    }
 
    init_ps_display(NULL);
 
    SetProcessingMode(BootstrapProcessing);
    IgnoreSystemIndexes = true;
 
    /*
     * As an auxiliary process, we aren't going to do the full InitPostgres
     * pushups, but there are a couple of things that need to get lit up even
     * in an auxiliary process.
     */
 
    /*
     * Create a PGPROC so we can use LWLocks.  In the EXEC_BACKEND case, this
     * was already done by SubPostmasterMain().
     */
#ifndef EXEC_BACKEND
    InitAuxiliaryProcess();
#endif
 
    BaseInit();
 
    /*
     * Assign the ProcSignalSlot for an auxiliary process.  Since it doesn't
     * have a BackendId, the slot is statically allocated based on the
     * auxiliary process type (MyAuxProcType).  Backends use slots indexed in
     * the range from 1 to MaxBackends (inclusive), so we use MaxBackends +
     * AuxProcType + 1 as the index of the slot for an auxiliary process.
     *
     * This will need rethinking if we ever want more than one of a particular
     * auxiliary process type.
     */
    ProcSignalInit(MaxBackends + MyAuxProcType + 1);
 
    /*
     * Auxiliary processes don't run transactions, but they may need a
     * resource owner anyway to manage buffer pins acquired outside
     * transactions (and, perhaps, other things in future).
     */
    CreateAuxProcessResourceOwner();
 
 
    /* Initialize backend status information */
    pgstat_beinit();
    pgstat_bestart();
 
    /* register a before-shutdown callback for LWLock cleanup */
    before_shmem_exit(ShutdownAuxiliaryProcess, 0);
 
    SetProcessingMode(NormalProcessing);
 
    switch (MyAuxProcType)
    {
        case StartupProcess:
            StartupProcessMain();
            proc_exit(1);
 
        case ArchiverProcess:
            PgArchiverMain();
            proc_exit(1);
 
        case BgWriterProcess:
            BackgroundWriterMain();
            proc_exit(1);
 
        case CheckpointerProcess:
            CheckpointerMain();
            proc_exit(1);
 
        case WalWriterProcess:
            WalWriterMain();
            proc_exit(1);
 
        case WalReceiverProcess:
            WalReceiverMain();
            proc_exit(1);
 
        default:
            elog(PANIC, "unrecognized process type: %d", (int) MyAuxProcType);
            proc_exit(1);
    }
}
 
/*
 * Begin shutdown of an auxiliary process.  This is approximately the equivalent
 * of ShutdownPostgres() in postinit.c.  We can't run transactions in an
 * auxiliary process, so most of the work of AbortTransaction() is not needed,
 * but we do need to make sure we've released any LWLocks we are holding.
 * (This is only critical during an error exit.)
 */
static void
ShutdownAuxiliaryProcess(int code, Datum arg)
{
    LWLockReleaseAll();
    ConditionVariableCancelSleep();
    pgstat_report_wait_end();
}