6 ms·

> Most autoscalers barely even qualify as ‘bang bang’ controllers - they detect a need for more capacity, and add nodes at some artificially constrained rate un

> Most autoscalers barely even qualify as ‘bang bang’ controllers - they detect a need for more capacity, and add nodes at some artificially constrained rate until capacity is reached or they hit a max cluster size limit. Even rudimentary control theory is an improvement. Why do you think PID is an improvement here? IMHO the bang bang approach is preferable because it behaves extremely predictably. Operationally, knowing how the system will react to extreme conditions might be more valuable than being a little more optimal.

srean 5y ago
Parent's point is that they are worse than bang-bang controller. Its not very clear from your comment but are you claiming that PIDs are not predictable ?
- jcalvinowens 5y ago
  Huh? Parent was arguing in favor of it: "PID is a damn sight more sophisticated", "even rudimentary control theory is an improvement". Yes, PID upset is a real problem when things start going sideways, as they tend to occasionally in the real world.
  - rualca 5y ago
    > Huh? Parent was arguing in favor of it: "PID is a damn sight more sophisticated", "even rudimentary control theory is an improvement". You clearly failed to read (and quote) what OP said, and therefore understand his point. Please pay attention to OP's point that PID is more sophisticated with the current state of affairs, which don't even qualify as bang bang controllers. The OP quite clearly and unambiguously stated that "Even rudimentary control theory is an improvement." Just because you feel the need to one-up other people's work that does not mean it is ok you distort and strawman the points they made.
  - jameshart 5y ago
    My point was more that the idea of applying control theory is an improvement over doing what amounts to bang-bang control without really thinking about it. Not that PID is better, not that bang-bang is better, just that.. learning from control theory is likely a fruitful direction to go in. Most autos along algorithms have heuristically hacked hysteresis built in to stop them oscillating between provisioning a node, dropping a node, provisioning, dropping. That kind of threshold tuning stuff is ripe for replacement with something more rigorous. PID control is an example of a rigorous way to solve that in continuous control. It likely doesn’t directly work for capacity, but control theory in general does have better answers for this kind of thing than just PID.
    - jcalvinowens 5y ago
      Ok, I can agree with that.
ori_b 5y ago
> Operationally, knowing how the system will react to extreme conditions might be more valuable than being a little more optimal. With today's systems, we typically have neither.
jhgb 5y ago
> Operationally, knowing how the system will react to extreme conditions might be more valuable than being a little more optimal. But there's a lot of theory around PID control to show how PID control systems behave under all sorts of circumstances. Hell, there's even things that are mathematically provable, like for example stability, which I strongly suspect you may often not even be able to reason about in case of many an ad-hoc systems like the ones GP is talking about.
deleted 5y ago
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srean 5y ago

Parent's point is that they are worse than bang-bang controller. Its not very clear from your comment but are you claiming that PIDs are not predictable ?

jcalvinowens 5y ago
Huh? Parent was arguing in favor of it: "PID is a damn sight more sophisticated", "even rudimentary control theory is an improvement". Yes, PID upset is a real problem when things start going sideways, as they tend to occasionally in the real world.
- rualca 5y ago
  > Huh? Parent was arguing in favor of it: "PID is a damn sight more sophisticated", "even rudimentary control theory is an improvement". You clearly failed to read (and quote) what OP said, and therefore understand his point. Please pay attention to OP's point that PID is more sophisticated with the current state of affairs, which don't even qualify as bang bang controllers. The OP quite clearly and unambiguously stated that "Even rudimentary control theory is an improvement." Just because you feel the need to one-up other people's work that does not mean it is ok you distort and strawman the points they made.
- jameshart 5y ago
  My point was more that the idea of applying control theory is an improvement over doing what amounts to bang-bang control without really thinking about it. Not that PID is better, not that bang-bang is better, just that.. learning from control theory is likely a fruitful direction to go in. Most autos along algorithms have heuristically hacked hysteresis built in to stop them oscillating between provisioning a node, dropping a node, provisioning, dropping. That kind of threshold tuning stuff is ripe for replacement with something more rigorous. PID control is an example of a rigorous way to solve that in continuous control. It likely doesn’t directly work for capacity, but control theory in general does have better answers for this kind of thing than just PID.
  - jcalvinowens 5y ago
    Ok, I can agree with that.

ori_b 5y ago

> Operationally, knowing how the system will react to extreme conditions might be more valuable than being a little more optimal. With today's systems, we typically have neither.

jhgb 5y ago

> Operationally, knowing how the system will react to extreme conditions might be more valuable than being a little more optimal. But there's a lot of theory around PID control to show how PID control systems behave under all sorts of circumstances. Hell, there's even things that are mathematically provable, like for example stability, which I strongly suspect you may often not even be able to reason about in case of many an ad-hoc systems like the ones GP is talking about.

deleted 5y ago

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