Is there any way to append a record at the end of a file....something like what GFS has?
regards, On Mon, Mar 3, 2008 at 12:23 PM, dhruba Borthakur <[EMAIL PROTECTED]> wrote: > Hi Ahmad, > > In the current implementation of HDFS, files are "write-once". You > cannot change/modify the contents of a file once it is written. > > Thanks, > dhruba > > -----Original Message----- > From: Ahmad Humayun [mailto:[EMAIL PROTECTED] > Sent: Saturday, March 01, 2008 1:27 AM > To: [email protected] > Subject: Re: hdfsLock > > Well this is what I want to do. Lets say I have two nodes A & B each > working > with the HDFS. I have a file named, say, temp. In the file temp I just > store > a single integer (1 or 0). Now both these nodes access the file temp. > Everything in concept should work fine as long as both the nodes are > just > reading the file, but what if a Node has to change the integer inside > temp. > I think the normal procedure will be to read the temp file's integer, > delete > the file and write a new file temp with the new required value. Lets say > Node B wanted to go through this procedure of changing the value inside > temp. While Node B is "changing/writing" to temp, I don't want Node A to > be > able to either read or write to temp. Its something like 'flock()' > through > the same fd (file descriptor) > > In short I want exclusive access for the Node changing a file. Its the > Readers Writers problem :) > > > Thanks for the wonderful support on this mailing list :) > > regards, > > > On Fri, Feb 29, 2008 at 12:47 AM, Raghu Angadi <[EMAIL PROTECTED]> > wrote: > > > > > What do you want to use these locks for? From your question, you seem > to > > be concerned about multiple threads accessing a stream. FileLocks have > > nothing to do with that. They were meant to be something like > 'flock()' > > system call. > > > > Raghu. > > > > Ahmad Humayun wrote: > > > Do you any reason why? Is it because only one thread can write to a > > specific > > > file in the hdfs at a single time....and multiple simultaneous > readers > > > doesn't cause any problem...hence locks make no sense in this > > situation??? > > > > > > thanks for the help. > > > > > > > > > regards, > > > > > > On Thu, Feb 28, 2008 at 10:28 PM, Raghu Angadi > <[EMAIL PROTECTED]> > > > wrote: > > > > > >> File locking is not supported in HDFS. Not sure if it ever was > > supported > > >> properly. This interface was deprecated last year. > > >> > > >> Raghu. > > >> > > >> Ahmad Humayun wrote: > > >>> Hello everyone, > > >>> > > >>> Does anybody have an idea why hdfsLock and hdfsReleaseLock been > taken > > >> out of > > >>> libhdfs? How do I lock a file now using libhdfs? Can somebody > point me > > >> to > > >>> the changelog or smth? > > >>> > > >>> > > >>> regards, > > >> > > > > > > > > > > > > > -- > Ahmad Humayun > Research Assistant > Computer Science Dpt., LUMS > +92 321 4457315 > -- Ahmad Humayun Research Assistant Computer Science Dpt., LUMS +92 321 4457315
