Shuffle the segments when rebalancing the table to avoid creating hotspot servers #5197
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…spot servers When new servers are added to an existing replica-group based table and rebalance is triggered, current behavior will assign segments in alphabetical order, which might move only the new segments to the new added servers. Because queries tend to query the most recent segments, this behavior might cause new added servers to become the hotspot servers. To address this issue, we shuffle the segments so that old and new segments can be balanced assigned. We use the hash of the table name as the random seed to shuffle the segments so that the result is deterministic. It is a little bit tricky to write a test case for this. Since the change is straight-forward and the existing tests already have pretty good coverage, after manually verified the expected behavior, no new test is added.
siddharthteotia
approved these changes
Mar 31, 2020
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When new servers are added to an existing replica-group based table
and rebalance is triggered, current behavior will assign segments
in alphabetical order, which might move only the new segments to
the new added servers. Because queries tend to query the most recent
segments, this behavior might cause new added servers to become the
hotspot servers.
To address this issue, we shuffle the segments so that old and new
segments can be balanced assigned.
We use the hash of the table name as the random seed to shuffle the
segments so that the result is deterministic.
It is a little bit tricky to write a test case for this. Since the
change is straight-forward and the existing tests already have
pretty good coverage, after manually verified the expected behavior,
no new test is added.