Re: FreeBSD UFS & fsync
On Mon, Feb 22, 2021 at 10:38 PM Thomas Munro wrote: > Do you have WCE enabled? In that case, modern Linux file systems > would do a synchronous SYNCHRONIZE CACHE for our WAL fdatasync(), but > FreeBSD UFS wouldn't as far as I know. It does know how to do that > (there's a BIO_FLUSH operation, also used by ZFS), but as far as I can > see UFS uses it just for its own file system meta-data crash safety > currently (see softdep_synchronize()). (There is also no FUA flag for > O_[D]SYNC writes, an even more modern invention.) Apparently no WCE, but I could be looking at the wrong piece: % sysctl kern.cam.ada | grep write_cache kern.cam.ada.2.write_cache: -1 kern.cam.ada.1.write_cache: -1 kern.cam.ada.0.write_cache: -1 kern.cam.ada.write_cache: -1 I'm using sata disks, not scsi. Assuming I'm not looking at the wrong parameter, I wil attach a scsi disk to do the same test and see if something changes. Or if you have any other suggestion about what to inspect, please advice. Thanks, Luca
Re: FreeBSD UFS & fsync
On Tue, Feb 23, 2021 at 5:49 AM Luca Ferrari wrote: > I'm running a virtual machine with FreeBSD 12.2, PostgreSQL 12.5 and > UFS as filesystem. > I was experimenting with fsync = off and pgbench, and I see no > particular difference in tps having fsync enabled or disabled. > Now, the same tiny test on a linux box provides a 10x tps, while on > FreeBSD is a 1% increase. > I'm trying to figure out why, and I suspect there is something related > to how UFS handles writes. Do you have WCE enabled? In that case, modern Linux file systems would do a synchronous SYNCHRONIZE CACHE for our WAL fdatasync(), but FreeBSD UFS wouldn't as far as I know. It does know how to do that (there's a BIO_FLUSH operation, also used by ZFS), but as far as I can see UFS uses it just for its own file system meta-data crash safety currently (see softdep_synchronize()). (There is also no FUA flag for O_[D]SYNC writes, an even more modern invention.)
FreeBSD UFS & fsync
Hi all, I'm running a virtual machine with FreeBSD 12.2, PostgreSQL 12.5 and UFS as filesystem. I was experimenting with fsync = off and pgbench, and I see no particular difference in tps having fsync enabled or disabled. Now, the same tiny test on a linux box provides a 10x tps, while on FreeBSD is a 1% increase. I'm trying to figure out why, and I suspect there is something related to how UFS handles writes. Any particular advice about tuning and parameters that can be affecting the "no difference" with fsync turned off? % sudo tunefs -p /dev/gpt/DATA tunefs: POSIX.1e ACLs: (-a)disabled tunefs: NFSv4 ACLs: (-N)disabled tunefs: MAC multilabel: (-l) disabled tunefs: soft updates: (-n)disabled tunefs: soft update journaling: (-j) disabled tunefs: gjournal: (-J) disabled tunefs: trim: (-t)enabled tunefs: maximum blocks per file in a cylinder group: (-e) 8192 tunefs: average file size: (-f)16384 tunefs: average number of files in a directory: (-s) 64 tunefs: minimum percentage of free space: (-m) 8% tunefs: space to hold for metadata blocks: (-k)6408 tunefs: optimization preference: (-o) time tunefs: volume label: (-L) DATA
