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35 lines
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ReStructuredText
35 lines
1.2 KiB
ReStructuredText
ScyllaDB consistency quiz for administrators
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**Topic: Architecture and development**
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**Learn: Understanding consistency in ScyllaDB: a quiz**
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**Audience: ScyllaDB administrators**
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Q: When you run ``nodetool decommission`` to remove a node…
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1. Will the token range the node had be relocated to other nodes?
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What about vnodes?
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2. When and how will we know the “decommission” operation is finished?
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A1. Yes. The node enters the state “STATE\_LEAVING” while streaming its
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data to other nodes. Then it is in “STATE\_LEFT” when the data has been
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streamed.
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A2. Use ``nodetool netstats`` to check the state of a node.
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Q: Let's say I have a 16 node cluster using Network Topology Strategy
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across 2 data centers. The replication factor is TWO in each datacenter
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(DC1: 2, DC2: 2). If I write using a LOCAL\_QUORUM, I will write the
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data to 4 nodes (2 in each data center) but when will the
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acknowledgement happen?
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A: The acknowledgment will be sent to the user when two **local** replicas respond.
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In this case, floor(local_RF/2 +1) = 2 , so LOCAL\_QUORUM is equal to RF per DC, which is why RF of 3 is usually better.
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:doc:`Knowledge Base </kb/index>`
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