为什么全复制 Cassandra 集群有节点数据大小差异

Question

I have a 3-node cassandra cluster (version 3.11.11) with replication factor 3. only 2 of the nodes are receiving requests, and Node3 only sync with the other 2 nodes.

In theory, each node should have the same data size. But in practice, I end up with nodes with different data sizes as shown in the picture.

we have daily nodetool repair , operations like compaction are done automatically with default settings.

What can be the reason for the size difference?

Answer 1

It finally ends up how data gets compacted in the long run. Since compaction is local process and how sstables can be stacked up cannot be guaranteed. So I dont see any abbreviation here. Theory just say all nodes will have same data logically but physically it may vary. For example in node3 you may have old sstables that are not getting compacted due to size (if using STCS) and in other nodes they have compacted and reduced the size of those nodes.