pg_test_fsync.c

Go to the documentation of this file.

/*
 *  pg_test_fsync.c
 *      tests all supported fsync() methods
 */

#include "postgres_fe.h"

#include <sys/stat.h>
#include <sys/time.h>
#include <fcntl.h>
#include <time.h>
#include <unistd.h>
#include <signal.h>

#include "getopt_long.h"
#include "access/xlogdefs.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) \
    { \
        fprintf(stderr, _("Could not create thread for alarm\n")); \
        exit(1); \
    } \
    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 int  secs_per_test = 5;
static int  needs_unlink = 0;
static char full_buf[DEFAULT_XLOG_SEG_SIZE],
           *buf,
           *filename = FSYNC_FILENAME;
static struct timeval start_t,
            stop_t;
static bool 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(int sig);
#else
static DWORD WINAPI process_alarm(LPVOID param);
#endif
static void signal_cleanup(int sig);

#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);
static void die(const char *str);


int
main(int argc, char *argv[])
{
    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);
#ifndef WIN32
    pqsignal(SIGALRM, process_alarm);
#endif
#ifdef SIGHUP
    /* Not defined on win32 */
    pqsignal(SIGHUP, signal_cleanup);
#endif

    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 */

    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 = strdup(optarg);
                break;

            case 's':
                secs_per_test = atoi(optarg);
                break;

            default:
                fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
                        progname);
                exit(1);
                break;
        }
    }

    if (argc > optind)
    {
        fprintf(stderr,
                _("%s: too many command-line arguments (first is \"%s\")\n"),
                progname, argv[optind]);
        fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
                progname);
        exit(1);
    }

    printf(ngettext("%d second per test\n",
                    "%d seconds per test\n",
                    secs_per_test),
           secs_per_test);
#if PG_O_DIRECT != 0
    printf(_("O_DIRECT 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++)
        full_buf[ops] = random();

    buf = (char *) TYPEALIGN(XLOG_BLCKSZ, full_buf);
}

static void
test_open(void)
{
    int         tmpfile;

    /*
     * test if we can open the target file
     */
    if ((tmpfile = open(filename, O_RDWR | O_CREAT, S_IRUSR | S_IWUSR)) == -1)
        die("could not open output file");
    needs_unlink = 1;
    if (write(tmpfile, full_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 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 OPEN_DATASYNC_FLAG
    if ((tmpfile = open(filename, O_RDWR | O_DSYNC | PG_O_DIRECT, 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 (write(tmpfile, buf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
                    die("write failed");
            if (lseek(tmpfile, 0, SEEK_SET) == -1)
                die("seek failed");
        }
        STOP_TIMER;
        close(tmpfile);
    }
#else
    printf(NA_FORMAT, _("n/a"));
#endif

/*
 * Test fdatasync if available
 */
    printf(LABEL_FORMAT, "fdatasync");
    fflush(stdout);

#ifdef HAVE_FDATASYNC
    if ((tmpfile = open(filename, O_RDWR, 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 (write(tmpfile, buf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
                die("write failed");
        fdatasync(tmpfile);
        if (lseek(tmpfile, 0, SEEK_SET) == -1)
            die("seek failed");
    }
    STOP_TIMER;
    close(tmpfile);
#else
    printf(NA_FORMAT, _("n/a"));
#endif

/*
 * Test fsync
 */
    printf(LABEL_FORMAT, "fsync");
    fflush(stdout);

    if ((tmpfile = open(filename, O_RDWR, 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 (write(tmpfile, buf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
                die("write failed");
        if (fsync(tmpfile) != 0)
            die("fsync failed");
        if (lseek(tmpfile, 0, SEEK_SET) == -1)
            die("seek 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, 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 (write(tmpfile, buf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
                die("write failed");
        if (pg_fsync_writethrough(tmpfile) != 0)
            die("fsync failed");
        if (lseek(tmpfile, 0, SEEK_SET) == -1)
            die("seek 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 OPEN_SYNC_FLAG
    if ((tmpfile = open(filename, O_RDWR | OPEN_SYNC_FLAG | PG_O_DIRECT, 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 (write(tmpfile, buf, 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");
            if (lseek(tmpfile, 0, SEEK_SET) == -1)
                die("seek 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 OPEN_SYNC_FLAG
    int         tmpfile,
                ops,
                writes;
#endif

    printf(LABEL_FORMAT, msg);
    fflush(stdout);

#ifdef OPEN_SYNC_FLAG
    if ((tmpfile = open(filename, O_RDWR | OPEN_SYNC_FLAG | PG_O_DIRECT, 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 (write(tmpfile, buf, writes_size * 1024) !=
                    writes_size * 1024)
                    die("write failed");
            if (lseek(tmpfile, 0, SEEK_SET) == -1)
                die("seek 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, 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, 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, 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, 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);

    START_TIMER;
    for (ops = 0; alarm_triggered == false; ops++)
    {
        if ((tmpfile = open(filename, O_RDWR, 0)) == -1)
            die("could not open output file");
        if (write(tmpfile, buf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
            die("write failed");
        close(tmpfile);
    }
    STOP_TIMER;
}

static void
signal_cleanup(int signum)
{
    /* Delete the file if it exists. Ignore errors */
    if (needs_unlink)
        unlink(filename);
    /* Finish incomplete line on stdout */
    puts("");
    exit(signum);
}

#ifdef HAVE_FSYNC_WRITETHROUGH

static int
pg_fsync_writethrough(int fd)
{
#ifdef WIN32
    return _commit(fd);
#elif 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(int sig)
{
    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

static void
die(const char *str)
{
    fprintf(stderr, _("%s: %s\n"), _(str), strerror(errno));
    exit(1);
}