Re: [pgsql-hackers-win32] SRA Win32 sync() code
От | Bruce Momjian |
---|---|
Тема | Re: [pgsql-hackers-win32] SRA Win32 sync() code |
Дата | |
Msg-id | 200311170546.hAH5kYn17867@candle.pha.pa.us обсуждение исходный текст |
Ответ на | Re: [pgsql-hackers-win32] SRA Win32 sync() code (Tom Lane <tgl@sss.pgh.pa.us>) |
Ответы |
Re: [pgsql-hackers-win32] SRA Win32 sync() code
(Shridhar Daithankar <shridhar_daithankar@persistent.co.in>)
Re: [pgsql-hackers-win32] SRA Win32 sync() code (Kurt Roeckx <Q@ping.be>) |
Список | pgsql-patches |
Tom Lane wrote: > > Do we know that having the background writer fsync a file that was > > written by a backend cause all the data to fsync? I think I could write > > a program to test this by timing each of these tests: > > That might prove something about the particular platform you tested it > on; but it would not speak to the real problem, which is what we can > assume is true on every platform... The attached program does test if fsync can be used on a file descriptor after the file is closed and then reopened. I see: write 0.000613 write & fsync 0.001727 write, close & fsync 0.001633 This shows that fsync works even after the file is closed and reopened. I could test by writing using a subprocess, but I don't see how that would be different, and it would mess up my timings. Anyway, if we find all our platforms can pass this test, we might be able to allow backends to do their own writes and just record the file name somewhere for the checkpointer to fsync. It also shows write/fsync was 3x slower than simple write. Does anyone have a platform where the last duration is significantly different from the middle timing? I am keeping this discussion on patches because of the C program attachment. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073 /* * test_fsync.c * tests if fsync can be done from another process than the original write */ #include <sys/types.h> #include <fcntl.h> #include <stdio.h> #include <time.h> #include <unistd.h> void die(char *str); void print_elapse(struct timeval start_t, struct timeval elapse_t); int main(int argc, char *argv[]) { struct timeval start_t; struct timeval elapse_t; int tmpfile; int i; char charout = 44; /* write only */ gettimeofday(&start_t, NULL); if ((tmpfile = open("/var/tmp/test_fsync.out", O_RDWR | O_CREAT)) == -1) die("can't open /var/tmp/test_fsync.out"); for (i = 0; i < 200; i++) write(tmpfile, &charout, 1); close(tmpfile); gettimeofday(&elapse_t, NULL); unlink("/var/tmp/test_fsync.out"); printf("write "); print_elapse(start_t, elapse_t); printf("\n"); /* write & fsync */ gettimeofday(&start_t, NULL); if ((tmpfile = open("/var/tmp/test_fsync.out", O_RDWR | O_CREAT)) == -1) die("can't open /var/tmp/test_fsync.out"); for (i = 0; i < 200; i++) write(tmpfile, &charout, 1); fsync(tmpfile); close(tmpfile); gettimeofday(&elapse_t, NULL); unlink("/var/tmp/test_fsync.out"); printf("write & fsync "); print_elapse(start_t, elapse_t); printf("\n"); /* write, close & fsync */ gettimeofday(&start_t, NULL); if ((tmpfile = open("/var/tmp/test_fsync.out", O_RDWR | O_CREAT)) == -1) die("can't open /var/tmp/test_fsync.out"); for (i = 0; i < 200; i++) write(tmpfile, &charout, 1); close(tmpfile); /* reopen file */ if ((tmpfile = open("/var/tmp/test_fsync.out", O_RDWR | O_CREAT)) == -1) die("can't open /var/tmp/test_fsync.out"); fsync(tmpfile); close(tmpfile); gettimeofday(&elapse_t, NULL); unlink("/var/tmp/test_fsync.out"); printf("write, close & fsync "); print_elapse(start_t, elapse_t); printf("\n"); return 0; } void print_elapse(struct timeval start_t, struct timeval elapse_t) { if (elapse_t.tv_usec < start_t.tv_usec) { elapse_t.tv_sec--; elapse_t.tv_usec += 1000000; } printf("%ld.%06ld", (long) (elapse_t.tv_sec - start_t.tv_sec), (long) (elapse_t.tv_usec - start_t.tv_usec)); } void die(char *str) { fprintf(stderr, "%s", str); exit(1); }
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