At Tue, 27 Aug 2019 15:49:32 +0900 (Tokyo Standard Time), Kyotaro Horiguchi
<horikyota....@gmail.com> wrote in
<20190827.154932.250364935.horikyota....@gmail.com>
> 128GB shared buffers contain 16M buffers. On my
> perhaps-Windows-Vista-era box, such loop takes 15ms. (Since it
> has only 6GB, the test is ignoring the effect of cache that comes
> from the difference of the buffer size). (attached 1)
...
> For a 16MB file, the cost of write-fsyncing cost is almost the
> same to that of WAL-emitting cost. It was about 200 ms on the
> Vista-era machine with non-performant rotating magnetic disks
> with xfs. (attached 2, 3) Although write-fsyncing of relation
> file makes no lock conflict with other backends, WAL-emitting
> delays other backends' commits at most by that milliseconds.
FWIW, the attached are the programs I used to take the numbers.
testloop.c: to take time to loop over buffers in FlushRelationBuffers
testfile.c: to take time to sync a heap file. (means one file for the size)
testfile2.c: to take time to emit a wal record. (means 16MB per file)
regards.
--
Kyotaro Horiguchi
NTT Open Source Software Center
#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
typedef struct RelFileNode
{
unsigned int spc;
unsigned int db;
unsigned int rel;
} RelFileNode;
typedef struct Buffer
{
RelFileNode rnode;
} Buffer;
//#define NBUFFERS ((int)((128.0 * 1024 * 1024 * 1024) / (8.0 * 1024)))
#define NBUFFERS ((int)((32.0 * 1024 * 1024 * 1024) / (8.0 * 1024)))
int main(void) {
int i;
RelFileNode t = {1,2,3};
Buffer *bufs = (Buffer *) malloc(sizeof(Buffer) * NBUFFERS);
struct timeval st, ed;
int matches = 0, unmatches = 0;
Buffer *b;
for (i = 0 ; i < NBUFFERS ; i++) {
bufs[i].rnode.spc = random() * 100;
bufs[i].rnode.db = random() * 100;
bufs[i].rnode.rel = random() * 10000;
}
/* start measuring */
gettimeofday(&st, NULL);
b = bufs;
for (i = 0 ; i < NBUFFERS ; i++) {
if (b->rnode.spc == t.spc && b->rnode.db == t.db && b->rnode.rel ==
t.rel)
matches++;
else
unmatches++;
b++;
}
gettimeofday(&ed, NULL);
printf("%lf ms for %d loops, matches %d, unmatches %d\n",
(double)((ed.tv_sec - st.tv_sec) * 1000.0 +
(ed.tv_usec - st.tv_usec) / 1000.0),
i, matches, unmatches);
return 0;
}
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/time.h>
#include <fcntl.h>
//#define FILE_SIZE (16 * 1024 * 1024)
//#define LOOPS 100
#define FILE_SIZE (64 * 1024)
#define LOOPS 1000
//#define FILE_SIZE (8 * 1024)
//#define LOOPS 1000
//#define FILE_SIZE (1 * 1024)
//#define LOOPS 1000
//#define FILE_SIZE (512)
//#define LOOPS 1000
//#define FILE_SIZE (128)
//#define LOOPS 1000
char buf[FILE_SIZE];
char fname[256];
int main(void) {
int i, j;
int fd = -1;
struct timeval st, ed;
double accum = 0.0;
int bufperfile = (int)((16.0 * 1024 * 1024) / FILE_SIZE);
for (i = 0 ; i < LOOPS ; i++) {
snprintf(fname, 256, "test%03d.file", i);
unlink(fname); // ignore errors
}
for (i = 0 ; i < LOOPS ; i++) {
for (j = 0 ; j < FILE_SIZE ; j++)
buf[j] = random()* 256;
if (i % bufperfile == 0) {
if (fd >= 0)
close(fd);
snprintf(fname, 256, "test%03d.file", i / bufperfile);
fd = open(fname, O_CREAT | O_RDWR, 0644);
if (fd < 0) {
fprintf(stderr, "open error: %m\n");
exit(1);
}
memset(buf, 0, sizeof(buf));
if (write(fd, buf, sizeof(buf)) < 0) {
fprintf(stderr, "init write error: %m\n");
exit(1);
}
if (fsync(fd) < 0) {
fprintf(stderr, "init fsync error: %m\n");
exit(1);
}
if (lseek(fd, 0, SEEK_SET) < 0) {
fprintf(stderr, "init lseek error: %m\n");
exit(1);
}
}
gettimeofday(&st, NULL);
if (write(fd, buf, FILE_SIZE) < 0) {
fprintf(stderr, "write error: %m\n");
exit(1);
}
if (fdatasync(fd) < 0) {
fprintf(stderr, "fdatasync error: %m\n");
exit(1);
}
gettimeofday(&ed, NULL);
accum += (double)((ed.tv_sec - st.tv_sec) * 1000.0 +
(ed.tv_usec - st.tv_usec) / 1000.0);
}
printf("%.2lf ms for %d %dkB-records (%d MB), %.2lf ms per %dkB)\n",
accum, i, FILE_SIZE / 1024, i * FILE_SIZE, accum / i,
FILE_SIZE / 1024);
return 0;
}
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/time.h>
#include <fcntl.h>
//#define FILE_SIZE (16 * 1024 * 1024)
//#define LOOPS 100
//#define FILE_SIZE (8 * 1024)
//#define LOOPS 1000
//#define FILE_SIZE (1 * 1024)
//#define LOOPS 1000
//#define FILE_SIZE (512)
//#define LOOPS 1000
#define FILE_SIZE (128)
#define LOOPS 1000
char buf[FILE_SIZE];
int main(void) {
int i;
int fd = -1;
double accum = 0.0;
struct timeval st, ed;
for (i = 0 ; i < LOOPS ; i++) {
char fname[256];
snprintf(fname, 256, "test%03d.file", i);
unlink(fname); // ignore errors
}
for (i = 0 ; i < LOOPS ; i++) {
char fname[256];
int j;
snprintf(fname, 256, "test%03d.file", i);
for (j = 0 ; j < FILE_SIZE ; j++)
buf[j] = random()* 256;
if (fd >= 0)
close(fd);
gettimeofday(&st, NULL);
fd = open(fname, O_CREAT | O_RDWR, 0644);
if (fd < 0) {
fprintf(stderr, "open error: %m\n");
exit(1);
}
if (write(fd, buf, FILE_SIZE) < 0) {
fprintf(stderr, "write error: %m\n");
exit(1);
}
if (fdatasync(fd) < 0) {
fprintf(stderr, "fdatasync error: %m\n");
exit(1);
}
if (lseek(fd, 0, SEEK_SET) < 0) {
fprintf(stderr, "lseek error: %m\n");
exit(1);
}
gettimeofday(&ed, NULL);
accum += (double)((ed.tv_sec - st.tv_sec) * 1000.0 +
(ed.tv_usec - st.tv_usec) / 1000.0);
}
printf("%.2lf ms for %d %dkB-files (%d MB), %.2lf ms per %dkB)\n",
accum, i, FILE_SIZE / 1024, i * FILE_SIZE, accum / i,
FILE_SIZE / 1024);
return 0;
}
