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From "Max Pfingsthorn" <>
Subject making pipelines wait for each other
Date Mon, 06 Feb 2006 09:44:06 GMT

I am not sure what has been done about this so far, but we are still experiencing some not-so-great
behavior from the CachingPipeline:
We have some pipelines which take a long time to complete processing, like generating a homepage
from many different sources. We see that if a second request for exactly the same pipeline
comes in before the first request is done, it takes again as long because the first pipeline
did not put its result in the cache yet and it is recomputed. This is quite obvious, but hurts
our performance a lot.

I was thinking that we might implement some thread synchronization by sharing some objects
and calling wait() and notify() on them.

First I thought putting an empty CachedResponse into the Cache when we start generating the
data. Any pipeline trying to access that CachedResponse will notice that it is empty and call
wait() on it. As soon as the first pipeline is done saving its content to the cache, it calls
notify(). Then I remembered that the Cache puts these on disk, and I am not sure what happens
to the locks when an object is serialized...
So, what about doing the same with a store instead? We push an empty response into a store,
preferrably a transient, in-memory one without size limits, and do the same as I outlined

WDYT? Would that solve it? Is there a better way?

Best regards,

Max Pfingsthorn


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