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Prerequisite: The cache meta of querycoord records which sealed segments and growing segments are loaded on each query node, and which dmchannels are watched by the query node. These metas are stored synchronously in etcd at the same time.
1.First of all, querycoord automatically generates handoff tasks and load balance tasks and writes them into etcd, and then clears them from etcd until the task is completed, ensuring that querycoord can accurately restore the task after restarting.
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4.After query coord successfully loads sealed segments on querynode, update the sealed segments list of each querynode in cache meta. For example, after balancing sealed segment 8 from node 1 to node 2, the meta of node1 changes from {S6, S7,S8} to { S6, S7}, node2's meta is changed from {S5} to {S5, S8}. If the query node suddenly goes down, directly follow the meta records of the coord to recover the query node. While querycoord updates the meta, it sends a change info of sealed segments to querychannel. The proto of sealed segments change info is as follows:
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