greelkorke ment using a job queue where jobs are put, and handed to workers.
If you want to do it only with mongo, you'll need to use some "lock" document, that is set and unset by the first process which tries to initiate a task. All other processes which try to grab the lock while its held by another process should assume that the job is being worked by another process. But thats really ugly & has problems because jobs cant be acknowledged, so if a process crashes while its performing some task, you're fucked. On Fri, Oct 5, 2012 at 5:07 PM, Tom <tommed...@gmail.com> wrote: > Unfortunately I'm afraid that I don't see how a scheduler can avoid the > concurrency problems. Note that the advantages (e.g. in availability) of > having a cluster should be maintained here, and so you cannot run a > scheduler in a separate process on a single server. If every server would > be running the scheduler, the same concurrency problems would arise. What > were you proposing? > > About the initialization, I guess that would work. It is not the way I > would prefer to do it, as I would like the application to be > self-controlled and usable without running special tools, but I reckon it > is an acceptable approach. > > Tom > > Op vrijdag 5 oktober 2012 19:59:33 UTC+7 schreef greelgorke het volgende: > >> i wouldn't do it that way. when deploying your app just do a pre-start >> script, that ensures the existence of your desired data. >> If you have periodical tasks, it's best to use a lib for it, that >> triggers jobs appart of your main application. i.E >> http://stackoverflow.com/**questions/3785736/is-there-a-** >> job-scheduler-library-for-**node-js<http://stackoverflow.com/questions/3785736/is-there-a-job-scheduler-library-for-node-js>, >> so you just avoid the concurrency problems. >> >> Am Freitag, 5. Oktober 2012 14:04:58 UTC+2 schrieb Tom: >>> >>> I've setup a cluster of physical servers. Each server runs exactly the >>> same code. Moreover, each server runs multiple node processes using >>> the build in cluster functionality. >>> >>> I use MongoDB (native) to share information between processes and >>> servers. However, I am having some difficulty with running a special task >>> that needs to be executed only once during initialization: >>> > if a special `admin` account does not yet exist in the database, it >>> should be created >>> >>> Originally I figured that I could read from the MongoDB master server on >>> each node and check if the admin account already exists. If it does not >>> then another node has not yet created it, so this node should do so. >>> However this is problematic because creating an admin password hash is >>> asynchronous and takes time. Therefore there is a delay between when a node >>> decides to create the account and when the account is being found by other >>> nodes when querying the database. >>> >>> The code snippet that reads from the Mongo master only and creates the >>> account is available here: >>> https://gist.github.com/**3839429<https://gist.github.com/3839429> >>> >>> In the future I would also like a special task to be executed every 5 >>> minutes. This task must then only be executed by a running server, and not >>> by all servers. >>> >>> In short: when running a cluster of servers, how do you coordinate >>> between these servers which of them is going to execute a sole task such as >>> the one described above? >>> >>> Tom >>> >> -- > Job Board: http://jobs.nodejs.org/ > Posting guidelines: > https://github.com/joyent/node/wiki/Mailing-List-Posting-Guidelines > You received this message because you are subscribed to the Google > Groups "nodejs" group. > To post to this group, send email to nodejs@googlegroups.com > To unsubscribe from this group, send email to > nodejs+unsubscr...@googlegroups.com > For more options, visit this group at > http://groups.google.com/group/nodejs?hl=en?hl=en > -- Job Board: http://jobs.nodejs.org/ Posting guidelines: https://github.com/joyent/node/wiki/Mailing-List-Posting-Guidelines You received this message because you are subscribed to the Google Groups "nodejs" group. To post to this group, send email to nodejs@googlegroups.com To unsubscribe from this group, send email to nodejs+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/nodejs?hl=en?hl=en
