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    • Iustin Pop's avatar
      htools: rework the algorithm for ChangeAll mode · 97da6b71
      Iustin Pop authored
      
      I think I've identified the problem with the current ChangeAll
      mode. The current algorithm works as follows:
      
      - identify a new primary by choosing the node which gives best score
        as new secondary
      - failover to it
      - identify a new secondary by choosing the node which gives best score
        as new secondary
      
      This means that the future primary is 'fixed' after the first
      iteration, leaving to possibly suboptimal results. This patch changes
      the algorithm to do what, in hindsight, seems the obvious thing to do:
      - generate all pairs (primary, secondary)
      - identify the pair that after the above sequence (r:np, f, r:ns)
        gives the best group score
      
      This fixes some of the corner cases I've seen in relocation, but not
      all; the remaining cases are related to multi-instance relocation and
      while they can't be fixed in the current framework, the needed
      rebalancing is much smaller than with the current algorithm.
      
      The patch also fixes an issue with the docstring of another function.
      
      Signed-off-by: default avatarIustin Pop <iustin@google.com>
      Reviewed-by: default avatarMichael Hanselmann <hansmi@google.com>
      97da6b71
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