Re: [GENERAL] True ACID under linux (no fsync)?
On 31 Oct 2000, Gary Howland wrote: Just a quickie - I heard that linux does not have a working fsync() call At least the manpage for fsync says that it does. The implementation: /* .. finally sync the buffers to disk */ dev = inode-i_dev; return sync_buffers(dev, 1); It really looks like it IS implemented. But probably on Linux not just the file data/metadata is synced, also all that device's data, which makes it very inefficient, but presumably `safe'. NB: don't forget that fsync() merely ensures that data was sent to the disk controller. Maybe this one has a cache (e.g. a fast SCSI harddrive), and if power fails, well. If fsync() was calling the SCSI FLUSH command, maybe that could be done, but that would not just sync the file.
Re: [GENERAL] True ACID under linux (no fsync)?
Strange. I did a test on Redhat Linux 7.0 with fsync() turned off and my batchfile of inserts ran 10 times as fast. But that was on an slow PC with a slow IDE harddrive. What Linux distribution and kernel version are you running? Poul L. Christiansen "Gary Howland (During daytime)" wrote: Hi, Just a quickie - I heard that linux does not have a working fsync() call (it has no concept of raw devices). In other words, fsync cannot be used to ensure that data is on disk (try it with a floppy - it returns IMMEDIATELY!!! - long before the write finishes) This is for ALL linuxes. Does this mean that postgres is unrealiable (or non ACID-conforming) under linux? Gary -- Friends help you move. Real friends help you move bodies. ___ Free Unlimited Internet Access! Try it now! http://www.zdnet.com/downloads/altavista/index.html ___
Re: [GENERAL] True ACID under linux (no fsync)?
I must have missed that one. How do you turn off fsync()?? I have lots of batch loading to do during which ACID is of no use. ++ kevin "Poul L. Christiansen" wrote: Strange. I did a test on Redhat Linux 7.0 with fsync() turned off and my batchfile of inserts ran 10 times as fast. But that was on an slow PC with a slow IDE harddrive. What Linux distribution and kernel version are you running? Poul L. Christiansen "Gary Howland (During daytime)" wrote: Hi, Just a quickie - I heard that linux does not have a working fsync() call (it has no concept of raw devices). In other words, fsync cannot be used to ensure that data is on disk (try it with a floppy - it returns IMMEDIATELY!!! - long before the write finishes) This is for ALL linuxes. Does this mean that postgres is unrealiable (or non ACID-conforming) under linux? Gary -- Friends help you move. Real friends help you move bodies. ___ Free Unlimited Internet Access! Try it now! http://www.zdnet.com/downloads/altavista/index.html ___ -- Kevin O'Gorman (805) 650-6274 mailto:[EMAIL PROTECTED] Permanent e-mail forwarder: mailto:Kevin.O'[EMAIL PROTECTED] At school: mailto:[EMAIL PROTECTED] Web: http://www.cs.ucsb.edu/~kogorman/index.html Web: http://trixie.kosman.via.ayuda.com/~kevin/index.html "There is a freedom lying beyond circumstance, derived from the direct intuition that life can be grounded upon its absorption in what is changeless amid change" -- Alfred North Whitehead
Re: [GENERAL] True ACID under linux (no fsync)?
Use the "-F" option. I start PostgreSQL with this line: su -l postgres -c "/usr/bin/pg_ctl -D $PGDATA -p /usr/bin/postmaster -o '-i -B 4096 -o -F' start /dev/null 21" /dev/null Poul L. Christiansen Kevin O'Gorman wrote: I must have missed that one. How do you turn off fsync()?? I have lots of batch loading to do during which ACID is of no use. ++ kevin "Poul L. Christiansen" wrote: Strange. I did a test on Redhat Linux 7.0 with fsync() turned off and my batchfile of inserts ran 10 times as fast. But that was on an slow PC with a slow IDE harddrive. What Linux distribution and kernel version are you running? Poul L. Christiansen "Gary Howland (During daytime)" wrote: Hi, Just a quickie - I heard that linux does not have a working fsync() call (it has no concept of raw devices). In other words, fsync cannot be used to ensure that data is on disk (try it with a floppy - it returns IMMEDIATELY!!! - long before the write finishes) This is for ALL linuxes. Does this mean that postgres is unrealiable (or non ACID-conforming) under linux? Gary -- Friends help you move. Real friends help you move bodies. ___ Free Unlimited Internet Access! Try it now! http://www.zdnet.com/downloads/altavista/index.html ___ -- Kevin O'Gorman (805) 650-6274 mailto:[EMAIL PROTECTED] Permanent e-mail forwarder: mailto:Kevin.O'[EMAIL PROTECTED] At school: mailto:[EMAIL PROTECTED] Web: http://www.cs.ucsb.edu/~kogorman/index.html Web: http://trixie.kosman.via.ayuda.com/~kevin/index.html "There is a freedom lying beyond circumstance, derived from the direct intuition that life can be grounded upon its absorption in what is changeless amid change" -- Alfred North Whitehead
Re: [GENERAL] True ACID under linux (no fsync)?
Use the "-F" option. I start PostgreSQL with this line: su -l postgres -c "/usr/bin/pg_ctl -D $PGDATA -p /usr/bin/postmaster -o '-i -B 4096 -o -F' start /dev/null 21" /dev/null Interesting... trying to start postgres 7.0.2 with the "-F" simply returns a list of options to me, as if it can't understand it. It sure does sound appealing to me, though. With a few hundred megs of disk cache (between the kernel and the RAID controller), I've always wished that PostgreSQL would take advantage of it when writing. : ) steve
Re: [GENERAL] True ACID under linux (no fsync)?
On Tue, 31 Oct 2000, Steve Wolfe wrote: Interesting... trying to start postgres 7.0.2 with the "-F" simply returns a list of options to me, as if it can't understand it. It sure does sound appealing to me, though. With a few hundred megs of disk cache (between the kernel and the RAID controller), I've always wished that PostgreSQL would take advantage of it when writing. : ) postmaster -o -F -D /your/datadirectory The -o tells postmaster to pass -F as backend option. man postmaster and man postgres for more information. -- Dominic J. Eidson "Baruk Khazad! Khazad ai-menu!" - Gimli --- http://www.the-infinite.org/ http://www.the-infinite.org/~dominic/
Re: [GENERAL] True ACID under linux (no fsync)?
"Gary Howland (During daytime)" wrote: Hi, Just a quickie - I heard that linux does not have a working fsync() call (it has no concept of raw devices). In other words, fsync cannot be used to ensure that data is on disk (try it with a floppy - it returns IMMEDIATELY!!! - long before the write finishes) Are you sure? Where is this information? This is for ALL linuxes. Does this mean that postgres is unrealiable (or non ACID-conforming) under linux? Gary -- Friends help you move. Real friends help you move bodies. ___ Free Unlimited Internet Access! Try it now! http://www.zdnet.com/downloads/altavista/index.html ___
Re: [GENERAL] True ACID under linux (no fsync)?
I may be horriblly out of my element here but, I'm going to jump in anyway :) If you mount a floppy and copy a large file to it, you will get a prompt back fairly quickly. If you type: sync right after The sync command writes everything to the floppy as expected. Shawn On Tue, 31 Oct 2000, markw wrote: "Gary Howland (During daytime)" wrote: Hi, Just a quickie - I heard that linux does not have a working fsync() call (it has no concept of raw devices). In other words, fsync cannot be used to ensure that data is on disk (try it with a floppy - it returns IMMEDIATELY!!! - long before the write finishes) Are you sure? Where is this information? This is for ALL linuxes. Does this mean that postgres is unrealiable (or non ACID-conforming) under linux? Gary -- Friends help you move. Real friends help you move bodies. ___ Free Unlimited Internet Access! Try it now! http://www.zdnet.com/downloads/altavista/index.html ___
Re: [GENERAL] True ACID under linux (no fsync)?
"Gary Howland (During daytime)" wrote: Just a quickie - I heard that linux does not have a working fsync() call (it has no concept of raw devices). In other words, fsync cannot be used to ensure that data is on disk (try it with a floppy - it returns IMMEDIATELY!!! - long before the write finishes) That's because the mounted drive is buffered in memory, so when you copy a file, you are copying it to memory (which is very fast), and the kernel implicitly syncs with the media when the buffer fills or when an explicit sync is done or when it is unmounted. If there is no working fsync (and fdatasync), why do the Linux man pages claim it to be POSIX.1b compliant? Can you back up your claim with actual documentation? Saying 'I heard' puts it in the realm of urban legendry... Brett W. McCoy http://www.chapelperilous.net --- This is the LAST time I take travel suggestions from Ray Bradbury!
Re: [GENERAL] True ACID under linux (no fsync)?
shawn everett wrote: I may be horriblly out of my element here but, I'm going to jump in anyway :) If you mount a floppy and copy a large file to it, you will get a prompt back fairly quickly. If you type: sync right after The sync command writes everything to the floppy as expected. Yes, but does cp call fsync()? That is the question. I would suspect that it does not. A non-functional fsync call is a serious error, and one should think more people would mention it. This is the first I have heard. Shawn On Tue, 31 Oct 2000, markw wrote: "Gary Howland (During daytime)" wrote: Hi, Just a quickie - I heard that linux does not have a working fsync() call (it has no concept of raw devices). In other words, fsync cannot be used to ensure that data is on disk (try it with a floppy - it returns IMMEDIATELY!!! - long before the write finishes) Are you sure? Where is this information? This is for ALL linuxes. Does this mean that postgres is unrealiable (or non ACID-conforming) under linux? Gary -- Friends help you move. Real friends help you move bodies. ___ Free Unlimited Internet Access! Try it now! http://www.zdnet.com/downloads/altavista/index.html ___
