Hi, > Hi all, > > When testing PostgreSQL, I found a performance degradation. After some > investigation, it ultimately reached the attached simple C program and > turned out that the performance degradation happens on only the xfs > filesystem (doesn't happen on neither ext3 nor ext4). In short, the > program alternately does two things to extend a file (1) call > posix_fallocate() to extend by 8192 bytes and (2) call pwrite() to > extend by 8192 bytes. If I do only either (1) or (2), the program is > completed in 2 sec, but if I do (1) and (2) alternatively, it is > completed in 90 sec. > > $ gcc -o test test.c > $ time ./test test.1 1 > total 200000 > fallocate 200000 > filewrite 0 > > real 0m1.305s > user 0m0.050s > sys 0m1.255s > > $ time ./test test.2 2 > total 200000 > fallocate 100000 > filewrite 100000 > > real 1m29.222s > user 0m0.139s > sys 0m3.139s > > Why does it take so long in the latter case? and are there any > workaround or configuration changes to deal with it? > I test it on xfs linux 6.1.35 and 6.4-rc7 the result is almost same. $ time ./test test.1 1 real 0m1.382s $ time ./test test.2 2 real 0m9.262s linunx kernel version please. Best Regards Wang Yugui (wangyugui@xxxxxxxxxxxx) 2023/06/22
