[rrd-users] NO ERROR returns trying to update the rrd file which no longer exits.

Andreas Maus A.Maus at science-computing.de
Tue Oct 5 10:24:44 CEST 2010


Just a wild guess. rrdcached has a file handle for this file.
If you delete a file the OS usually removes the directory entry
but NOT the allocated space.

A file handles point to an inode not to a path, so I think rrdcached
is still able to write data to the file handle.

If you remove a file using rm, rm calls the "unlink" function
(which destroys a "link" between a filename (a dentry) and a file).

The file _actually_ still exits until the reference counter (of the
file handles for this file) is zero (which only happens if you close
the last open file handle).

The write() system call (I guess rrdcached uses this call) doesn't return
ENOENT if you write to a file handle (see man 2 write) and rrdcached
passes the errno of the system calls (in this case the system call returns
with errno=0).

"rrdtool update" on the other hand will call open() to get a _NEW_ file handle
each time it access a file. If the path to the file doesn't exist
it returns ENOENT because it is not able to acquire a NEW file handle.

The solution? I don't know. Does rrdcached close a file handle if you
pass the flush command?



On 10/05/10 09:59, 橋本 雄弥 wrote:
> Hello,
> Trying to update the rrd file which no longer existed with use of rrdcached via network,
> I recieved NO ERROR, which should have returned. (And, the message would be "ERROR: rrdcached: No such file: xxxxxx", I suppose.)
> The procedure I went through when I came across this event was as follows;
> (Assume that Host A and Host B are connected via network)
> 1. Run rrdcached on HOST A.
> 2. Create a rrd file on HOST A.
> 3. Execute "rrdtool update --daemon" on HOST B to udpate the rrd file created on HOST A.
> NO ERROR returned, which seemed normal.
> 4. Remove the rrd file from HOST A.
> 5.Execute "rrdtool update --daemon" on HOST B to udpate the rrd file already removed from HOST A.
> NO ERROR returned, which seemed strange since there no longer existed the rrd file what should be updated.
> The event described above doesn't happen if "rrdtool update" is executed on the same host on which target rrd file
> is located.
> The version of RRDtool used is 1.4.4.
> Does anyone have the information or the solution about this?
> Regards,
> Yuya
> _______________________________________________
> rrd-users mailing list
> rrd-users at lists.oetiker.ch
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