pg_test_fsync.c

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/*-------------------------------------------------------------------------
 *
 * pg_test_fsync --- tests all supported fsync() methods
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 *
 * src/bin/pg_test_fsync/pg_test_fsync.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres_fe.h"
 
#include <limits.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <fcntl.h>
#include <time.h>
#include <unistd.h>
#include <signal.h>
 
#include "common/logging.h"
#include "common/pg_prng.h"
#include "getopt_long.h"
 
/*
 * put the temp files in the local directory
 * unless the user specifies otherwise
 */
#define FSYNC_FILENAME  "./pg_test_fsync.out"
 
#define XLOG_BLCKSZ_K   (XLOG_BLCKSZ / 1024)
 
#define LABEL_FORMAT        "        %-30s"
#define NA_FORMAT           "%21s\n"
/* translator: maintain alignment with NA_FORMAT */
#define OPS_FORMAT          gettext_noop("%13.3f ops/sec  %6.0f usecs/op\n")
#define USECS_SEC           1000000
 
/* These are macros to avoid timing the function call overhead. */
#ifndef WIN32
#define START_TIMER \
do { \
    alarm_triggered = false; \
    alarm(secs_per_test); \
    gettimeofday(&start_t, NULL); \
} while (0)
#else
/* WIN32 doesn't support alarm, so we create a thread and sleep there */
#define START_TIMER \
do { \
    alarm_triggered = false; \
    if (CreateThread(NULL, 0, process_alarm, NULL, 0, NULL) == \
        INVALID_HANDLE_VALUE) \
        pg_fatal("could not create thread for alarm"); \
    gettimeofday(&start_t, NULL); \
} while (0)
#endif
 
#define STOP_TIMER  \
do { \
    gettimeofday(&stop_t, NULL); \
    print_elapse(start_t, stop_t, ops); \
} while (0)
 
 
static const char *progname;
 
static unsigned int secs_per_test = 5;
static int  needs_unlink = 0;
alignas(PGAlignedXLogBlock) static char buf[DEFAULT_XLOG_SEG_SIZE];
static char *filename = FSYNC_FILENAME;
static struct timeval start_t,
            stop_t;
static sig_atomic_t alarm_triggered = false;
 
 
static void handle_args(int argc, char *argv[]);
static void prepare_buf(void);
static void test_open(void);
static void test_non_sync(void);
static void test_sync(int writes_per_op);
static void test_open_syncs(void);
static void test_open_sync(const char *msg, int writes_size);
static void test_file_descriptor_sync(void);
 
#ifndef WIN32
static void process_alarm(SIGNAL_ARGS);
#else
static DWORD WINAPI process_alarm(LPVOID param);
#endif
static void signal_cleanup(SIGNAL_ARGS);
 
#ifdef HAVE_FSYNC_WRITETHROUGH
static int  pg_fsync_writethrough(int fd);
#endif
static void print_elapse(struct timeval start_t, struct timeval stop_t, int ops);
 
#define die(msg) pg_fatal("%s: %m", _(msg))
 
 
int
main(int argc, char *argv[])
{
    pg_logging_init(argv[0]);
    set_pglocale_pgservice(argv[0], PG_TEXTDOMAIN("pg_test_fsync"));
    progname = get_progname(argv[0]);
 
    handle_args(argc, argv);
 
    /* Prevent leaving behind the test file */
    pqsignal(SIGINT, signal_cleanup);
    pqsignal(SIGTERM, signal_cleanup);
 
    /* the following are not valid on Windows */
#ifndef WIN32
    pqsignal(SIGALRM, process_alarm);
    pqsignal(SIGHUP, signal_cleanup);
#endif
 
    pg_prng_seed(&pg_global_prng_state, (uint64) time(NULL));
 
    prepare_buf();
 
    test_open();
 
    /* Test using 1 XLOG_BLCKSZ write */
    test_sync(1);
 
    /* Test using 2 XLOG_BLCKSZ writes */
    test_sync(2);
 
    test_open_syncs();
 
    test_file_descriptor_sync();
 
    test_non_sync();
 
    unlink(filename);
 
    return 0;
}
 
static void
handle_args(int argc, char *argv[])
{
    static struct option long_options[] = {
        {"filename", required_argument, NULL, 'f'},
        {"secs-per-test", required_argument, NULL, 's'},
        {NULL, 0, NULL, 0}
    };
 
    int         option;         /* Command line option */
    int         optindex = 0;   /* used by getopt_long */
    unsigned long optval;       /* used for option parsing */
    char       *endptr;
 
    if (argc > 1)
    {
        if (strcmp(argv[1], "--help") == 0 || strcmp(argv[1], "-?") == 0)
        {
            printf(_("Usage: %s [-f FILENAME] [-s SECS-PER-TEST]\n"), progname);
            exit(0);
        }
        if (strcmp(argv[1], "--version") == 0 || strcmp(argv[1], "-V") == 0)
        {
            puts("pg_test_fsync (PostgreSQL) " PG_VERSION);
            exit(0);
        }
    }
 
    while ((option = getopt_long(argc, argv, "f:s:",
                                 long_options, &optindex)) != -1)
    {
        switch (option)
        {
            case 'f':
                filename = pg_strdup(optarg);
                break;
 
            case 's':
                errno = 0;
                optval = strtoul(optarg, &endptr, 10);
 
                if (endptr == optarg || *endptr != '\0' ||
                    errno != 0 || optval != (unsigned int) optval)
                {
                    pg_log_error("invalid argument for option %s", "--secs-per-test");
                    pg_log_error_hint("Try \"%s --help\" for more information.", progname);
                    exit(1);
                }
 
                secs_per_test = (unsigned int) optval;
                if (secs_per_test == 0)
                    pg_fatal("%s must be in range %u..%u",
                             "--secs-per-test", 1, UINT_MAX);
                break;
 
            default:
                /* getopt_long already emitted a complaint */
                pg_log_error_hint("Try \"%s --help\" for more information.", progname);
                exit(1);
        }
    }
 
    if (argc > optind)
    {
        pg_log_error("too many command-line arguments (first is \"%s\")",
                     argv[optind]);
        pg_log_error_hint("Try \"%s --help\" for more information.", progname);
        exit(1);
    }
 
    printf(ngettext("%u second per test\n",
                    "%u seconds per test\n",
                    secs_per_test),
           secs_per_test);
#if defined(O_DIRECT)
    printf(_("O_DIRECT supported on this platform for open_datasync and open_sync.\n"));
#elif defined(F_NOCACHE)
    printf(_("F_NOCACHE supported on this platform for open_datasync and open_sync.\n"));
#else
    printf(_("Direct I/O is not supported on this platform.\n"));
#endif
}
 
static void
prepare_buf(void)
{
    int         ops;
 
    /* write random data into buffer */
    for (ops = 0; ops < DEFAULT_XLOG_SEG_SIZE; ops++)
        buf[ops] = (char) pg_prng_int32(&pg_global_prng_state);
}
 
static void
test_open(void)
{
    int         tmpfile;
 
    /*
     * test if we can open the target file
     */
    if ((tmpfile = open(filename, O_RDWR | O_CREAT | PG_BINARY, S_IRUSR | S_IWUSR)) == -1)
        die("could not open output file");
    needs_unlink = 1;
    if (write(tmpfile, buf, DEFAULT_XLOG_SEG_SIZE) !=
        DEFAULT_XLOG_SEG_SIZE)
        die("write failed");
 
    /* fsync now so that dirty buffers don't skew later tests */
    if (fsync(tmpfile) != 0)
        die("fsync failed");
 
    close(tmpfile);
}
 
static int
open_direct(const char *path, int flags, mode_t mode)
{
    int         fd;
 
#ifdef O_DIRECT
    flags |= O_DIRECT;
#endif
 
    fd = open(path, flags, mode);
 
#if !defined(O_DIRECT) && defined(F_NOCACHE)
    if (fd >= 0 && fcntl(fd, F_NOCACHE, 1) < 0)
    {
        int         save_errno = errno;
 
        close(fd);
        errno = save_errno;
        return -1;
    }
#endif
 
    return fd;
}
 
static void
test_sync(int writes_per_op)
{
    int         tmpfile,
                ops,
                writes;
    bool        fs_warning = false;
 
    if (writes_per_op == 1)
        printf(_("\nCompare file sync methods using one %dkB write:\n"), XLOG_BLCKSZ_K);
    else
        printf(_("\nCompare file sync methods using two %dkB writes:\n"), XLOG_BLCKSZ_K);
    printf(_("(in \"wal_sync_method\" preference order, except fdatasync is Linux's default)\n"));
 
    /*
     * Test open_datasync if available
     */
    printf(LABEL_FORMAT, "open_datasync");
    fflush(stdout);
 
#ifdef O_DSYNC
    if ((tmpfile = open_direct(filename, O_RDWR | O_DSYNC | PG_BINARY, 0)) == -1)
    {
        printf(NA_FORMAT, _("n/a*"));
        fs_warning = true;
    }
    else
    {
        START_TIMER;
        for (ops = 0; alarm_triggered == false; ops++)
        {
            for (writes = 0; writes < writes_per_op; writes++)
                if (pg_pwrite(tmpfile,
                              buf,
                              XLOG_BLCKSZ,
                              writes * XLOG_BLCKSZ) != XLOG_BLCKSZ)
                    die("write failed");
        }
        STOP_TIMER;
        close(tmpfile);
    }
#else
    printf(NA_FORMAT, _("n/a"));
#endif
 
/*
 * Test fdatasync if available
 */
    printf(LABEL_FORMAT, "fdatasync");
    fflush(stdout);
 
    if ((tmpfile = open(filename, O_RDWR | PG_BINARY, 0)) == -1)
        die("could not open output file");
    START_TIMER;
    for (ops = 0; alarm_triggered == false; ops++)
    {
        for (writes = 0; writes < writes_per_op; writes++)
            if (pg_pwrite(tmpfile,
                          buf,
                          XLOG_BLCKSZ,
                          writes * XLOG_BLCKSZ) != XLOG_BLCKSZ)
                die("write failed");
        fdatasync(tmpfile);
    }
    STOP_TIMER;
    close(tmpfile);
 
/*
 * Test fsync
 */
    printf(LABEL_FORMAT, "fsync");
    fflush(stdout);
 
    if ((tmpfile = open(filename, O_RDWR | PG_BINARY, 0)) == -1)
        die("could not open output file");
    START_TIMER;
    for (ops = 0; alarm_triggered == false; ops++)
    {
        for (writes = 0; writes < writes_per_op; writes++)
            if (pg_pwrite(tmpfile,
                          buf,
                          XLOG_BLCKSZ,
                          writes * XLOG_BLCKSZ) != XLOG_BLCKSZ)
                die("write failed");
        if (fsync(tmpfile) != 0)
            die("fsync failed");
    }
    STOP_TIMER;
    close(tmpfile);
 
/*
 * If fsync_writethrough is available, test as well
 */
    printf(LABEL_FORMAT, "fsync_writethrough");
    fflush(stdout);
 
#ifdef HAVE_FSYNC_WRITETHROUGH
    if ((tmpfile = open(filename, O_RDWR | PG_BINARY, 0)) == -1)
        die("could not open output file");
    START_TIMER;
    for (ops = 0; alarm_triggered == false; ops++)
    {
        for (writes = 0; writes < writes_per_op; writes++)
            if (pg_pwrite(tmpfile,
                          buf,
                          XLOG_BLCKSZ,
                          writes * XLOG_BLCKSZ) != XLOG_BLCKSZ)
                die("write failed");
        if (pg_fsync_writethrough(tmpfile) != 0)
            die("fsync failed");
    }
    STOP_TIMER;
    close(tmpfile);
#else
    printf(NA_FORMAT, _("n/a"));
#endif
 
/*
 * Test open_sync if available
 */
    printf(LABEL_FORMAT, "open_sync");
    fflush(stdout);
 
#ifdef O_SYNC
    if ((tmpfile = open_direct(filename, O_RDWR | O_SYNC | PG_BINARY, 0)) == -1)
    {
        printf(NA_FORMAT, _("n/a*"));
        fs_warning = true;
    }
    else
    {
        START_TIMER;
        for (ops = 0; alarm_triggered == false; ops++)
        {
            for (writes = 0; writes < writes_per_op; writes++)
                if (pg_pwrite(tmpfile,
                              buf,
                              XLOG_BLCKSZ,
                              writes * XLOG_BLCKSZ) != XLOG_BLCKSZ)
 
                    /*
                     * This can generate write failures if the filesystem has
                     * a large block size, e.g. 4k, and there is no support
                     * for O_DIRECT writes smaller than the file system block
                     * size, e.g. XFS.
                     */
                    die("write failed");
        }
        STOP_TIMER;
        close(tmpfile);
    }
#else
    printf(NA_FORMAT, _("n/a"));
#endif
 
    if (fs_warning)
    {
        printf(_("* This file system and its mount options do not support direct\n"
                 "  I/O, e.g. ext4 in journaled mode.\n"));
    }
}
 
static void
test_open_syncs(void)
{
    printf(_("\nCompare open_sync with different write sizes:\n"));
    printf(_("(This is designed to compare the cost of writing 16kB in different write\n"
             "open_sync sizes.)\n"));
 
    test_open_sync(_(" 1 * 16kB open_sync write"), 16);
    test_open_sync(_(" 2 *  8kB open_sync writes"), 8);
    test_open_sync(_(" 4 *  4kB open_sync writes"), 4);
    test_open_sync(_(" 8 *  2kB open_sync writes"), 2);
    test_open_sync(_("16 *  1kB open_sync writes"), 1);
}
 
/*
 * Test open_sync with different size files
 */
static void
test_open_sync(const char *msg, int writes_size)
{
#ifdef O_SYNC
    int         tmpfile,
                ops,
                writes;
#endif
 
    printf(LABEL_FORMAT, msg);
    fflush(stdout);
 
#ifdef O_SYNC
    if ((tmpfile = open_direct(filename, O_RDWR | O_SYNC | PG_BINARY, 0)) == -1)
        printf(NA_FORMAT, _("n/a*"));
    else
    {
        START_TIMER;
        for (ops = 0; alarm_triggered == false; ops++)
        {
            for (writes = 0; writes < 16 / writes_size; writes++)
                if (pg_pwrite(tmpfile,
                              buf,
                              writes_size * 1024,
                              writes * writes_size * 1024) !=
                    writes_size * 1024)
                    die("write failed");
        }
        STOP_TIMER;
        close(tmpfile);
    }
#else
    printf(NA_FORMAT, _("n/a"));
#endif
}
 
static void
test_file_descriptor_sync(void)
{
    int         tmpfile,
                ops;
 
    /*
     * Test whether fsync can sync data written on a different descriptor for
     * the same file.  This checks the efficiency of multi-process fsyncs
     * against the same file. Possibly this should be done with writethrough
     * on platforms which support it.
     */
    printf(_("\nTest if fsync on non-write file descriptor is honored:\n"));
    printf(_("(If the times are similar, fsync() can sync data written on a different\n"
             "descriptor.)\n"));
 
    /*
     * first write, fsync and close, which is the normal behavior without
     * multiple descriptors
     */
    printf(LABEL_FORMAT, "write, fsync, close");
    fflush(stdout);
 
    START_TIMER;
    for (ops = 0; alarm_triggered == false; ops++)
    {
        if ((tmpfile = open(filename, O_RDWR | PG_BINARY, 0)) == -1)
            die("could not open output file");
        if (write(tmpfile, buf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
            die("write failed");
        if (fsync(tmpfile) != 0)
            die("fsync failed");
        close(tmpfile);
 
        /*
         * open and close the file again to be consistent with the following
         * test
         */
        if ((tmpfile = open(filename, O_RDWR | PG_BINARY, 0)) == -1)
            die("could not open output file");
        close(tmpfile);
    }
    STOP_TIMER;
 
    /*
     * Now open, write, close, open again and fsync This simulates processes
     * fsyncing each other's writes.
     */
    printf(LABEL_FORMAT, "write, close, fsync");
    fflush(stdout);
 
    START_TIMER;
    for (ops = 0; alarm_triggered == false; ops++)
    {
        if ((tmpfile = open(filename, O_RDWR | PG_BINARY, 0)) == -1)
            die("could not open output file");
        if (write(tmpfile, buf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
            die("write failed");
        close(tmpfile);
        /* reopen file */
        if ((tmpfile = open(filename, O_RDWR | PG_BINARY, 0)) == -1)
            die("could not open output file");
        if (fsync(tmpfile) != 0)
            die("fsync failed");
        close(tmpfile);
    }
    STOP_TIMER;
}
 
static void
test_non_sync(void)
{
    int         tmpfile,
                ops;
 
    /*
     * Test a simple write without fsync
     */
    printf(_("\nNon-sync'ed %dkB writes:\n"), XLOG_BLCKSZ_K);
    printf(LABEL_FORMAT, "write");
    fflush(stdout);
 
    if ((tmpfile = open(filename, O_RDWR | PG_BINARY, 0)) == -1)
        die("could not open output file");
    START_TIMER;
    for (ops = 0; alarm_triggered == false; ops++)
    {
        if (pg_pwrite(tmpfile, buf, XLOG_BLCKSZ, 0) != XLOG_BLCKSZ)
            die("write failed");
    }
    STOP_TIMER;
    close(tmpfile);
}
 
static void
signal_cleanup(SIGNAL_ARGS)
{
    int         rc;
 
    /* Delete the file if it exists. Ignore errors */
    if (needs_unlink)
        unlink(filename);
    /* Finish incomplete line on stdout */
    rc = write(STDOUT_FILENO, "\n", 1);
    (void) rc;                  /* silence compiler warnings */
    _exit(1);
}
 
#ifdef HAVE_FSYNC_WRITETHROUGH
 
static int
pg_fsync_writethrough(int fd)
{
#if defined(F_FULLFSYNC)
    return (fcntl(fd, F_FULLFSYNC, 0) == -1) ? -1 : 0;
#else
    errno = ENOSYS;
    return -1;
#endif
}
#endif
 
/*
 * print out the writes per second for tests
 */
static void
print_elapse(struct timeval start_t, struct timeval stop_t, int ops)
{
    double      total_time = (stop_t.tv_sec - start_t.tv_sec) +
        (stop_t.tv_usec - start_t.tv_usec) * 0.000001;
    double      per_second = ops / total_time;
    double      avg_op_time_us = (total_time / ops) * USECS_SEC;
 
    printf(_(OPS_FORMAT), per_second, avg_op_time_us);
}
 
#ifndef WIN32
static void
process_alarm(SIGNAL_ARGS)
{
    alarm_triggered = true;
}
#else
static DWORD WINAPI
process_alarm(LPVOID param)
{
    /* WIN32 doesn't support alarm, so we create a thread and sleep here */
    Sleep(secs_per_test * 1000);
    alarm_triggered = true;
    ExitThread(0);
}
#endif