sticky balancer: try for better topic distribution among members #602
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The sticky balancer currently strives for ultimate stickiness, with no regard to trying to balance topic partitions among members equally. When adding a member, it is often the case that an entire topic's partitions shifts to the other member, while the first member has the other topic. By sorting by partition number before balancing, when the algorithm steals partitions from the end of an existing member to give to the new member, we ensure that we divvy up the topics equally to both members while still ensuring stickiness. This is likely not perfect but it goes a long way.
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The sticky balancer currently strives for ultimate stickiness, with no regard to trying to balance topic partitions among members equally. When adding a member, it is often the case that an entire topic's partitions shifts to the other member, while the first member has the other topic.
By sorting by partition number before balancing, when the algorithm steals partitions from the end of an existing member to give to the new member, we ensure that we divvy up the topics equally to both members while still ensuring stickiness.
This is likely not perfect but it goes a long way.