Hello,
I can set a watch on an object in librados. Does this object have to exist already at the moment I'm setting the watch on it? What happens if the object does not exist? Is my watcher valid? Will I get notified when someone else creates the missing object that I'm watching and sends a notification?
I believe a watch implicitly creates the object, but you could run it on a non-existent object and check. ;) but...
If the watch is not valid if the object has not yet been created then how can I get notified when the object is created? (I can imagine a work-around: there's an additional object, a kind of object registry object (the equivalent of a directory in a file system), that contains the list of created objects. I'm watching for modifications of the object registry object. Whenever a new object is created, the agent that creates the object also updates the object registry object.)
This is probably a better idea. Watches have a bit of overhead and while you can have a few per client without much trouble; if you're trying to watch a whole bunch of potential objects you probably want a stronger side channel communications system anyway, so using a set of communication objects and pushing the relevant data through them is likely to work better.
-Greg
Thank you,
Sorin
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