Track application restart generations #2564
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not that there’s a point in this test really
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[ci skip] [ci:skip]
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| TEST_METHOD(16) { | ||
| // Test that the correct process from the pool is routed |
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I know, I asked for help with this one.
| */ | ||
| Process * | ||
| Group::findEnabledProcessWithLowestBusyness() const { | ||
| Group::findBestEnabledProcess() const { |
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My head is clearer today and I thought of a problem with the routing algorithm. Recall that the algorithm has now turned into essentially this:
Select the first process according to the order
generation DESC, startTime ASC, busyness ASC.
This means that during a restart, new requests are only routed to next-generation processes, while previous-generation processes are only allowed to finish their existing requests. That's pretty bad.
I suggest a two-phase routing algorithm:
- First, we select the "best process" according to the algorithm as you have already coded in this branch.
- If it turns out that this process
isTotallyBusy(), then we fallback to the old algorithm where we select the least busy process amongst all generations. This way we won't waste the old processes.
What do you think?
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Makes more sense to me than the last algorithm.
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Also since we know we're going to punt if the process isTotallyBusy() there's no need to loop twice, just reject if isTotallyBusy() is true as we iterate.
It does raise another question though, what do we do if all processes are totally busy?
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I pushed a possible solution. I keep track of the best process which is totally busy, until I find one that is not totally busy, at the end of the loop I return either the best process which is not totally busy or if all processes are totally busy, then the best totally busy process.
The mechanism for choosing which process is best is decided as above for both processes, but tracked separately.
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The generation number groups all application processes according to the most recent restart initiation. We use this information to intelligently route to newer generations if there is capacity.
Fixes one aspect of #2551.