So this is a simple one, if I run the following code (see below) on Ubuntu 18.04 (4.15.0-29-generic ) and against Ubuntu 16.04 ( 4.4.0-87-generic) I get two different results ; The question is why? It seems that fsync may be broken in the latest kernel and may well be broken as early as 4.10 ? This has huge implications around performance sensitive applications like mysql. It also so worth noting that I'm running this against an ext4 filesystem with the following mount options rw,noatime,nodiratime,nobarrier,data=journal 4.4.0-87-generic - # time ./fsync real 0m7.537s <----- user 0m0.000s sys 0m1.060s <----- 4.15.0-29-generic - # time ./fsync real 1m38.299s <----- user 0m0.013s sys 0m0.893s <----- Linux buntu-1804 4.15.0-29-generic no sync() seconds:0.024438 writes per second:0.000000 sync() seconds:1.705764 writes per second:0.000000 real 3m6.475s user 0m0.006s sys 0m1.725s Linux ubuntu 4.4.0-87-generic no sync() seconds:0.012887 writes per second:0.000001 sync() seconds:0.736563 writes per second:0.000000 real 0m8.945s user 0m0.016s sys 0m0.732s #!/usr/bin/python import os, sys, mmap # Open a file fd = os.open( "/a/testfile", os.O_RDWR|os.O_CREAT|os.O_DIRECT ) m = mmap.mmap(-1, 512) for i in range (1,10000): os.lseek(fd,os.SEEK_SET,0) m[1] = "1" os.write(fd, m) os.fsync(fd) # Close opened file os.close( fd ) #define _GNU_SOURCE #include #include #include #include void withSync() { int f = open( "/a/t8" , O_RDWR | O_CREAT |O_DIRECT ); lseek (f, 0, SEEK_SET ); int records = 10*1000; clock_t ustart = clock(); for(int i = 0; i < records; i++) { write(f, "012345678901234567890123456789" , 30); fsync(f); } clock_t uend = clock(); close (f); printf(" sync() seconds:%lf writes per second:%lf\n", ((double)(uend-ustart))/(CLOCKS_PER_SEC), ((double)records)/((double)(uend-ustart))/(CLOCKS_PER_SEC)); } void withoutSync() { int f = open( "/a/t10" , O_RDWR | O_CREAT | O_DIRECT ); lseek (f, 0, SEEK_SET ); int records = 10*1000; clock_t ustart = clock(); for(int i = 0; i < records; i++) { write(f, "012345678901234567890123456789" , 30 ); } clock_t uend = clock(); close (f); printf("no sync() seconds:%lf writes per second:%lf \n", ((double)(uend-ustart))/(CLOCKS_PER_SEC), ((double)records)/((double)(uend-ustart))/(CLOCKS_PER_SEC)); } int main(int argc, const char * argv[]) { withoutSync(); withSync(); return 0; } Linux buntu-1804 4.15.0-29-generic no sync() seconds:0.024438 writes per second:0.000000 sync() seconds:1.705764 writes per second:0.000000 real 3m6.475s user 0m0.006s sys 0m1.725s Linux ubuntu 4.4.0-87-generic no sync() seconds:0.012887 writes per second:0.000001 sync() seconds:0.736563 writes per second:0.000000 real 0m8.945s user 0m0.016s sys 0m0.732s

When	Who	Action	New State
2018-08-02	actionparsnip	Answer	Answered
2018-08-02	Caron Wills	Comment	Answered
2018-08-02	Caron Wills	Comment	Answered

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