Question

Part of my latest webapp needs to write to file a fair amount as part of its logging. One problem I’ve noticed is that if there are a few concurrent users, the writes can overwrite each other (instead of appending to file). I assume this is because of the destination file can be open in a number of places at the same time.

flock(...) is usually superb but it doesn’t appear to work on NFS… Which is a huge problem for me as the production server uses a NFS array.

The closest thing I’ve seen to an actual solution involves trying to create a lock dir and waiting until it can be created. To say this lacks elegance is understatement of the year, possibly decade.

Any better ideas?

Edit: I should add that I don’t have root on the server and doing the storage in another way isn’t really feasible any time soon, not least within my deadline.

Answer 1

Another dirty hack would be to flock() a ‘local’ file, and only open / write to the NFS file if you hold the lock on the local file.

Edit: from the flock() page:

flock() will not work on NFS and many other networked file systems. Check your operating system documentation for more details.

Edit 2:

Of course there’s always using the database to synchonise access (I’m assuming your app uses a db). This would be quite a performance hit if you’re doing a lot of logging though.

If it’s just for logging, do you actually need a centralised log file? Could you log locally (and even combine the logs when they rotate at the end of the day if needed)?