[Gluster-devel] Issue about the size of fstat is less than the really size of the syslog file

Lian, George (Nokia - CN/Hangzhou) george.lian at nokia.com
Tue Nov 1 01:05:10 UTC 2016


Hi, Raghavendra,

Thanks a lots for your update!

>IIUC, the "tail issue" can happen if 'tail -f' reads a stat with st_size lesser than previously read value (and hence the complaint - file truncated). In this case, even though fstat at T2 doesn't account the write at T0, it doesn't prove that st_size of fstat at T2 is lesser than that at any time before T2.

I just mean the st_size of fstat maybe less than the previously read value in that time, and it will lead to the "tail truncated" issue. Do you agree with me?

>As to the relative ordering of write at T0 and fstat at T2, POSIX leaves it undefined. Unless write and fstat happen from same thread/single-threaded-application there is no requirement for maintaining that order (If they are issued from same thread fstat should account write at T0). Also note that it is not mentioned here fstat at T2 is issued _after_ write at T0 is _complete_. If that is the case, mdc_writev_cbk would've updated correct stat in cache and fstat would get correct value. If it is not the case, then there is no well defined order here.

>So, I don't think there is a bug here, unless I've missed out something.

Do you mean the GlusterFS not conflict with the requirement, so that the application like "tail" should consider the case in network file system?

@Jan & @Bingxuan, do you have some comments for the above information?


Best Regards,
George

-----Original Message-----
From: Raghavendra Gowdappa [mailto:rgowdapp at redhat.com] 
Sent: Monday, October 31, 2016 6:35 PM
To: Lian, George (Nokia - CN/Hangzhou) <george.lian at nokia.com>
Cc: Pranith Kumar Karampuri <pkarampu at redhat.com>; I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX_GMS <I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX at internal.nsn.com>; Zhang, Bingxuan (Nokia - CN/Hangzhou) <bingxuan.zhang at nokia.com>; Gluster-devel at gluster.org; Zizka, Jan (Nokia - CZ/Prague) <jan.zizka at nokia.com>
Subject: Re: [Gluster-devel] Issue about the size of fstat is less than the really size of the syslog file



----- Original Message -----
> From: "George Lian (Nokia - CN/Hangzhou)" <george.lian at nokia.com>
> To: "Pranith Kumar Karampuri" <pkarampu at redhat.com>, "Raghavendra Gowdappa" <rgowdapp at redhat.com>
> Cc: "I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX_GMS" <I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX at internal.nsn.com>, "Bingxuan Zhang (Nokia
> - CN/Hangzhou)" <bingxuan.zhang at nokia.com>, Gluster-devel at gluster.org, "Jan Zizka (Nokia - CZ/Prague)"
> <jan.zizka at nokia.com>
> Sent: Monday, October 31, 2016 2:32:34 PM
> Subject: RE: [Gluster-devel] Issue about the size of fstat is less than the really size of the syslog file
> 
> Hi,
> 
> I suppose there seems a defect on mdc_writev_cbk  and mdc_fstat
> Let’s assume in 2 timestamp which called write and fstat operation in
> application:
> T0:  write (process a)
> T1: read (process b) with the data of T0 of process a.
> T2: fstat   (process c)
> In my view, mdc_write is non-block operation and have some lock to protect in
> afr xlator,  because mdc_fstat not check the lock in AFR xaltor, so
> mdc_writev_cbk which called “mdc_inode_iatt_set_validate” maybe later than
> mdc_fstat.
> Such like
> T3: fstat result of T2  without the “mdc_inode_iatt_set_validate” of T0 when
> stat-prefetch options is on.
> T4: “mdc_inode_iatt_set_validate” is called of T0 in mdc_writev_cbk.
> 
> Lets’ assume T0<T1<T2<T3<T4, is the above assumption is reasonable case when
> in multi-process environment and the load of CPU is high?
> If it is reasonable, then issue of “tail issue” will be happened.

IIUC, the "tail issue" can happen if 'tail -f' reads a stat with st_size lesser than previously read value (and hence the complaint - file truncated). In this case, even though fstat at T2 doesn't account the write at T0, it doesn't prove that st_size of fstat at T2 is lesser than that at any time before T2.

As to the relative ordering of write at T0 and fstat at T2, POSIX leaves it undefined. Unless write and fstat happen from same thread/single-threaded-application there is no requirement for maintaining that order (If they are issued from same thread fstat should account write at T0). Also note that it is not mentioned here fstat at T2 is issued _after_ write at T0 is _complete_. If that is the case, mdc_writev_cbk would've updated correct stat in cache and fstat would get correct value. If it is not the case, then there is no well defined order here.

So, I don't think there is a bug here, unless I've missed out something.


> 
> So maybe a fix suggestion is on mdc_fstat operation , we should add an
> operation to check whether the writev operation is ongoing or not, if
> write-operation is ongoing, should goto uncached label in mdc_fstat
> function.
> 
> Could you please confirm the above assumption and suggestion?
> 
> 
> Thanks & Best Regards,
> George
> 
> 
> From: Lian, George (Nokia - CN/Hangzhou)
> Sent: Monday, October 31, 2016 4:25 PM
> To: Pranith Kumar Karampuri <pkarampu at redhat.com>; Raghavendra Gowdappa
> <rgowdapp at redhat.com>
> Cc: I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX_GMS
> <I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX at internal.nsn.com>; Zhang, Bingxuan (Nokia -
> CN/Hangzhou) <bingxuan.zhang at nokia.com>; Gluster-devel at gluster.org; Zizka,
> Jan (Nokia - CZ/Prague) <jan.zizka at nokia.com>
> Subject: RE: [Gluster-devel] Issue about the size of fstat is less than the
> really size of the syslog file
> 
> Hi,
> 
> How can we enable debug.trace so that we can inspect the debug data on
> different xlator?
> I just set “debug.trace on” and “debug.log-file yes” seems not work now.
> 
> And one more update for this issue, if we set performance.stat-prefetch to
> off, the issue will not be occurred. (our previous test maybe not correct☺ )
> 
> Thanks & Best Regards,
> George
> 
> From: Pranith Kumar Karampuri [mailto:pkarampu at redhat.com]
> Sent: Friday, October 28, 2016 2:39 PM
> To: Lian, George (Nokia - CN/Hangzhou)
> <george.lian at nokia.com<mailto:george.lian at nokia.com>>
> Cc: Raghavendra Gowdappa <rgowdapp at redhat.com<mailto:rgowdapp at redhat.com>>;
> I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX_GMS
> <I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX at internal.nsn.com<mailto:I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX at internal.nsn.com>>;
> Zhang, Bingxuan (Nokia - CN/Hangzhou)
> <bingxuan.zhang at nokia.com<mailto:bingxuan.zhang at nokia.com>>;
> Gluster-devel at gluster.org<mailto:Gluster-devel at gluster.org>; Zizka, Jan
> (Nokia - CZ/Prague) <jan.zizka at nokia.com<mailto:jan.zizka at nokia.com>>
> Subject: Re: [Gluster-devel] Issue about the size of fstat is less than the
> really size of the syslog file
> 
> hi George,
>        It would help if we can identify the bare minimum xlators which are
>        contributing to the issue like Raghavendra was mentioning earlier. We
>        were wondering if it is possible for you to help us in identifying
>        the issue by running the workload on a modified setup? We can suggest
>        testing out using custom volfiles so that we can slowly build the
>        graph which could be causing this issue. We would like you guys to
>        try out this problem with just posix-xlator and fuse and nothing
>        else.
> 
> On Thu, Oct 27, 2016 at 1:40 PM, Lian, George (Nokia - CN/Hangzhou)
> <george.lian at nokia.com<mailto:george.lian at nokia.com>> wrote:
> Hi, Raghavendra,
> 
> Could you please give some suggestion for this issue? we try to find the clue
> for this issue for a long time, but it has no progress:(
> 
> Thanks & Best Regards,
> George
> 
> -----Original Message-----
> From: Lian, George (Nokia - CN/Hangzhou)
> Sent: Wednesday, October 19, 2016 4:40 PM
> To: 'Raghavendra Gowdappa' <rgowdapp at redhat.com<mailto:rgowdapp at redhat.com>>
> Cc: Gluster-devel at gluster.org<mailto:Gluster-devel at gluster.org>;
> I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX_GMS
> <I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX at internal.nsn.com<mailto:I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX at internal.nsn.com>>;
> Zhang, Bingxuan (Nokia - CN/Hangzhou)
> <bingxuan.zhang at nokia.com<mailto:bingxuan.zhang at nokia.com>>; Zizka, Jan
> (Nokia - CZ/Prague) <jan.zizka at nokia.com<mailto:jan.zizka at nokia.com>>
> Subject: RE: [Gluster-devel] Issue about the size of fstat is less than the
> really size of the syslog file
> 
> Hi, Raghavendra
> 
> Just now, we test it with glusterfs log with debug-level "TRACE", and let
> some application trigger "glusterfs" produce large log, in that case, when
> we set write-behind and stat-prefetch both OFF,
> Tail the glusterfs log such like mnt-{VOLUME-NAME}.log, it still failed with
> "file truncated",
> 
> So that means if file's IO in huge amount, the issue will still be there even
> write-behind and stat-prefetch both OFF.
> 
> Best Regards,
> George
> 
> -----Original Message-----
> From: Raghavendra Gowdappa
> [mailto:rgowdapp at redhat.com<mailto:rgowdapp at redhat.com>]
> Sent: Wednesday, October 19, 2016 2:54 PM
> To: Lian, George (Nokia - CN/Hangzhou)
> <george.lian at nokia.com<mailto:george.lian at nokia.com>>
> Cc: Gluster-devel at gluster.org<mailto:Gluster-devel at gluster.org>;
> I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX_GMS
> <I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX at internal.nsn.com<mailto:I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX at internal.nsn.com>>;
> Zhang, Bingxuan (Nokia - CN/Hangzhou)
> <bingxuan.zhang at nokia.com<mailto:bingxuan.zhang at nokia.com>>; Zizka, Jan
> (Nokia - CZ/Prague) <jan.zizka at nokia.com<mailto:jan.zizka at nokia.com>>
> Subject: Re: [Gluster-devel] Issue about the size of fstat is less than the
> really size of the syslog file
> 
> 
> 
> ----- Original Message -----
> > From: "George Lian (Nokia - CN/Hangzhou)"
> > <george.lian at nokia.com<mailto:george.lian at nokia.com>>
> > To: "Raghavendra Gowdappa"
> > <rgowdapp at redhat.com<mailto:rgowdapp at redhat.com>>
> > Cc: Gluster-devel at gluster.org<mailto:Gluster-devel at gluster.org>,
> > "I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX_GMS"
> > <I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX at internal.nsn.com<mailto:I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX at internal.nsn.com>>,
> > "Bingxuan Zhang (Nokia - CN/Hangzhou)"
> > <bingxuan.zhang at nokia.com<mailto:bingxuan.zhang at nokia.com>>, "Jan Zizka
> > (Nokia - CZ/Prague)" <jan.zizka at nokia.com<mailto:jan.zizka at nokia.com>>
> > Sent: Wednesday, October 19, 2016 12:05:01 PM
> > Subject: RE: [Gluster-devel] Issue about the size of fstat is less than the
> > really size of the syslog file
> >
> > Hi, Raghavendra,
> >
> > Thanks a lots for your quickly update!
> > In my case, there are so many process(write) is writing to the syslog file,
> > it do involve the writer is in the same host and writing in same mount
> > point
> > while the tail(reader) is reading it.
> >
> > The bug I just guess is:
> > When a writer write the data with write-behind, it call the call-back
> > function " mdc_writev_cbk" and called "mdc_inode_iatt_set_validate" to
> > validate the "iatt" data, but with the code I mentioned last mail, it do
> > nothing.
> 
> mdc_inode_iatt_set_validate has following code
> 
> <snippet>
>                 if (!iatt || !iatt->ia_ctime) {
>                         mdc->ia_time = 0;
>                         goto unlock;
>                 }
> </snippet>
> 
> Which means a NULL iatt sets mdc->ia_time to 0. This results in subsequent
> lookup/stat calls to be NOT served from md-cache. Instead, the stat is
> served from backend bricks. So, I don't see an issue here.
> 
> However, one case where a NULL iatt is different from a valid iatt (which
> differs from the value stored in md-cache) is that the latter results in a
> call to inode_invalidate. This invalidation propagates to kernel and all
> dentry and page cache corresponding to file is purged. So, I am suspecting
> whether the stale stat you saw was served from kernel cache (not from
> glusterfs). If this is the case, having mount options "attribute-timeout=0"
> and "entry-timeout=0" should've helped.
> 
> I am still at loss to point out the RCA for this issue.
> 
> 
> > And in same time, the reader(tail) read the "iatt" data, but in case of the
> > cache-time is not timeout, it will return the "iatt" data without the last
> > change.
> >
> > Do your think it is a possible bug?
> >
> > Thanks & Best Regards,
> > George
> >
> > -----Original Message-----
> > From: Raghavendra Gowdappa
> > [mailto:rgowdapp at redhat.com<mailto:rgowdapp at redhat.com>]
> > Sent: Wednesday, October 19, 2016 2:06 PM
> > To: Lian, George (Nokia - CN/Hangzhou)
> > <george.lian at nokia.com<mailto:george.lian at nokia.com>>
> > Cc: Gluster-devel at gluster.org<mailto:Gluster-devel at gluster.org>;
> > I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX_GMS
> > <I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX at internal.nsn.com<mailto:I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX at internal.nsn.com>>;
> > Zhang, Bingxuan (Nokia -
> > CN/Hangzhou) <bingxuan.zhang at nokia.com<mailto:bingxuan.zhang at nokia.com>>;
> > Zizka, Jan (Nokia - CZ/Prague)
> > <jan.zizka at nokia.com<mailto:jan.zizka at nokia.com>>
> > Subject: Re: [Gluster-devel] Issue about the size of fstat is less than the
> > really size of the syslog file
> >
> >
> >
> > ----- Original Message -----
> > > From: "George Lian (Nokia - CN/Hangzhou)"
> > > <george.lian at nokia.com<mailto:george.lian at nokia.com>>
> > > To: "Raghavendra Gowdappa"
> > > <rgowdapp at redhat.com<mailto:rgowdapp at redhat.com>>
> > > Cc: Gluster-devel at gluster.org<mailto:Gluster-devel at gluster.org>,
> > > "I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX_GMS"
> > > <I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX at internal.nsn.com<mailto:I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX at internal.nsn.com>>,
> > > "Bingxuan Zhang (Nokia
> > > - CN/Hangzhou)"
> > > <bingxuan.zhang at nokia.com<mailto:bingxuan.zhang at nokia.com>>, "Jan Zizka
> > > (Nokia - CZ/Prague)"
> > > <jan.zizka at nokia.com<mailto:jan.zizka at nokia.com>>
> > > Sent: Wednesday, October 19, 2016 10:51:24 AM
> > > Subject: RE: [Gluster-devel] Issue about the size of fstat is less than
> > > the
> > > really size of the syslog file
> > >
> > > Hi, Raghavendra,
> > >
> > > When we disable md-cache(gluster volume set log
> > > performance.md-cache-timeout
> > > 0),  the issue seems gone.
> > > (we can't disable with " gluster volume set log performance.md-cache off"
> > > why?)
> >
> > Please use
> > #gluster volume set log performance.stat-prefetch off
> >
> > >
> > > So I double confuse that the code I abstract in last mail maybe have some
> > > issue for this case.
> > > Could you please share your comments?
> >
> > Please find my comments below.
> >
> > >
> > > Thanks & Best Regards,
> > > George
> > >
> > > -----Original Message-----
> > > From: Lian, George (Nokia - CN/Hangzhou)
> > > Sent: Friday, October 14, 2016 1:44 PM
> > > To: 'Raghavendra Gowdappa'
> > > <rgowdapp at redhat.com<mailto:rgowdapp at redhat.com>>
> > > Cc: Gluster-devel at gluster.org<mailto:Gluster-devel at gluster.org>;
> > > I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX_GMS
> > > <I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX at internal.nsn.com<mailto:I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX at internal.nsn.com>>;
> > > Zhang, Bingxuan (Nokia
> > > -
> > > CN/Hangzhou) <bingxuan.zhang at nokia.com<mailto:bingxuan.zhang at nokia.com>>;
> > > Zizka, Jan (Nokia - CZ/Prague)
> > > <jan.zizka at nokia.com<mailto:jan.zizka at nokia.com>>
> > > Subject: RE: [Gluster-devel] Issue about the size of fstat is less than
> > > the
> > > really size of the syslog file
> > >
> > > Hi, Raghavendra,
> > >
> > > Our version of GlusterFS is 3.6.9, and I also check the newest code of
> > > main
> > > branch, the function of " mdc_inode_iatt_set_validate" is almost same,
> > > from
> > > the following code of this function,
> > > We could see a "TODO" comments inline, does it mean if we enhance
> > > write-behind feature, the "iatt" field in callback will be NULL, so that
> > > inode_invalidate will not be called? So the size of file will not update
> > > since "write behind" enabled ?
> > > Is it the root cause for "tail" application failed with "file truncated"
> > > issue ?
> > >
> > >         LOCK (&mdc->lock);
> > >         {
> > >                 if (!iatt || !iatt->ia_ctime) {
> > >                         mdc->ia_time = 0;
> > >                         goto unlock;
> > >                 }
> > >
> > >             /*
> > >              * Invalidate the inode if the mtime or ctime has changed
> > >              * and the prebuf doesn't match the value we have cached.
> > >              * TODO: writev returns with a NULL iatt due to
> > >              * performance/write-behind, causing invalidation on writes.
> > >              */
> >
> > The issue explained in this comment is hit only when writes are done. But,
> > in
> > your use-case only "tail" is the application running on the mount (If I am
> > not wrong, the  writer is running on a different mountpoint). So, I doubt
> > you are hitting this issue. But, you are saying that the issue goes away
> > when write-behind/md-cache is turned off pointing to some interaction
> > between md-cache and write-behind causing the issue. I need more time to
> > look into this issue. Can you file a bug on this?
> >
> > >             if (IA_ISREG(inode->ia_type) &&
> > >                 ((iatt->ia_mtime != mdc->md_mtime) ||
> > >                 (iatt->ia_ctime != mdc->md_ctime)))
> > >                     if (!prebuf || (prebuf->ia_ctime != mdc->md_ctime) ||
> > >                         (prebuf->ia_mtime != mdc->md_mtime))
> > >                             inode_invalidate(inode);
> > >
> > >                 mdc_from_iatt (mdc, iatt);
> > >
> > >                 time (&mdc->ia_time);
> > >         }
> > >
> > > Best Regards,
> > > George
> > > -----Original Message-----
> > > From: Raghavendra Gowdappa
> > > [mailto:rgowdapp at redhat.com<mailto:rgowdapp at redhat.com>]
> > > Sent: Thursday, October 13, 2016 8:58 PM
> > > To: Lian, George (Nokia - CN/Hangzhou)
> > > <george.lian at nokia.com<mailto:george.lian at nokia.com>>
> > > Cc: Gluster-devel at gluster.org<mailto:Gluster-devel at gluster.org>;
> > > I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX_GMS
> > > <I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX at internal.nsn.com<mailto:I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX at internal.nsn.com>>;
> > > Zhang, Bingxuan (Nokia
> > > -
> > > CN/Hangzhou) <bingxuan.zhang at nokia.com<mailto:bingxuan.zhang at nokia.com>>;
> > > Zizka, Jan (Nokia - CZ/Prague)
> > > <jan.zizka at nokia.com<mailto:jan.zizka at nokia.com>>
> > > Subject: Re: [Gluster-devel] Issue about the size of fstat is less than
> > > the
> > > really size of the syslog file
> > >
> > >
> > >
> > > ----- Original Message -----
> > > > From: "George Lian (Nokia - CN/Hangzhou)"
> > > > <george.lian at nokia.com<mailto:george.lian at nokia.com>>
> > > > To: Gluster-devel at gluster.org<mailto:Gluster-devel at gluster.org>
> > > > Cc: "I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX_GMS"
> > > > <I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX at internal.nsn.com<mailto:I_EXT_MBB_WCDMA_SWD3_DA1_MATRIX at internal.nsn.com>>,
> > > > "Bingxuan Zhang
> > > > (Nokia
> > > > - CN/Hangzhou)"
> > > > <bingxuan.zhang at nokia.com<mailto:bingxuan.zhang at nokia.com>>, "Jan
> > > > Zizka (Nokia -
> > > > CZ/Prague)"
> > > > <jan.zizka at nokia.com<mailto:jan.zizka at nokia.com>>
> > > > Sent: Thursday, October 13, 2016 2:33:53 PM
> > > > Subject: [Gluster-devel] Issue about the size of fstat is less than the
> > > > really size of the syslog file
> > > >
> > > > Hi, Dear Expert,
> > > > We have use glusterfs as a network filesystem, and syslog store in
> > > > there,
> > > > some clients on different host may write the syslog file via
> > > > “glusterfs”
> > > > mount point.
> > > > Now we encounter an issue when we “tail” the syslog file, it will
> > > > occasional
> > > > failed with error “ file truncated ”
> > > > As we study and trace with the “tail” source code, it failed with the
> > > > following code:
> > > > if ( S_ISREG (mode) && stats.st_size < f[i].size )
> > > > {
> > > > error (0, 0, _("%s: file truncated"), quotef (name));
> > > > /* Assume the file was truncated to 0,
> > > > and therefore output all "new" data. */
> > > > xlseek (fd, 0, SEEK_SET, name);
> > > > f[i].size = 0;
> > > > }
> > > > When stats.st_size < f[i].size, what mean the size report by fstat is
> > > > less
> > > > than “tail” had read, it lead to “file truncated”, we also use “strace”
> > > > tools to trace the tail application, the related tail strace log as the
> > > > below:
> > > > nanosleep({1, 0}, NULL) = 0
> > > > fstat(3, {st_mode=S_IFREG|0644, st_size=192543105, ...}) = 0
> > > > nanosleep({1, 0}, NULL) = 0
> > > > fstat(3, {st_mode=S_IFREG|0644, st_size=192543105, ...}) = 0
> > > > nanosleep({1, 0}, NULL) = 0
> > > > fstat(3, {st_mode=S_IFREG|0644, st_size=192543105, ...}) = 0
> > > > nanosleep({1, 0}, NULL) = 0
> > > > fstat(3, {st_mode=S_IFREG|0644, st_size=192544549, ...}) = 0
> > > > read(3, " Data … -"..., 8192) = 1444
> > > > read(3, " Data.. "..., 8192) = 720
> > > > read(3, "", 8192) = 0
> > > > fstat(3, {st_mode=S_IFREG|0644, st_size=192544789, ...}) = 0
> > > > write(1, “DATA…..” ) = 2164
> > > > write(2, "tail: ", 6tail: ) = 6
> > > > write(2, "/mnt/log/master/syslog: file tru"...,
> > > > 38/mnt/log/master/syslog:
> > > > file truncated) = 38
> > > > as the above strace log, tail has read 1444+720=2164 bytes,
> > > > but fstat tell “tail” 192544789 – 192543105 = 1664 which less than
> > > > 2164,
> > > > so
> > > > it lead to “tail” application “file truncated”.
> > > > And if we turn off “write-behind” feature, the issue will not be
> > > > reproduced
> > > > any more.
> > >
> > > That seems strange. There are no writes happening on the fd/inode through
> > > which tail is reading/stating from. So, it seems strange that
> > > write-behind
> > > is involved here. I suspect whether any of md-cache/read-ahead/io-cache
> > > is
> > > causing the issue. Can you,
> > >
> > > 1. Turn off md-cache, read-ahead, io-cache xlators
> > > 2. mount glusterfs with --attribute-timeout=0
> > > 3. set write-behind on
> > >
> > > and rerun the tests? If you don't hit the issue, you can experiment by
> > > turning on/off of md-cache, read-ahead and io-cache translators and see
> > > what
> > > are the minimal number of xlators that need to be turned off to not hit
> > > the
> > > issue (with write-behind on)?
> > >
> > > regards,
> > > Raghavendra
> > >
> > > > So we think it may be related to cache consistence issue due to
> > > > performance
> > > > consider, but we still have concern that:
> > > > The syslog file is used only with “Append” mode, so the size of file
> > > > shouldn’t be reduced, when a client read the file, why “fstat” can’t
> > > > return
> > > > the really size match to the cache?
> > > > From current investigation, we doubt that the current implement of
> > > > “glusterfs” has a bug on “fstat” when cache is on.
> > > > Your comments is our highly appreciated!
> > > > Thanks & Best Regards
> > > > George
> > > >
> > > > _______________________________________________
> > > > Gluster-devel mailing list
> > > > Gluster-devel at gluster.org<mailto:Gluster-devel at gluster.org>
> > > > http://www.gluster.org/mailman/listinfo/gluster-devel
> > >
> >
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> --
> Pranith
> 


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