Drawbacks of Colocated Indexing and Search

Although the proposed design seems reasonable, there are a couple of serious drawbacks that we discuss below.

1. Colocation limiting scalability: In a practical system, searching and indexing scale differently with time. That is, depending on a partition, the indexing performed on one group of replicas may be resource-intensive. On the other hand, it is possible that some search queries are frequently performed which will result in a greater load on a group of replicas. Colocating both these operations on the same machine can lead to an imbalance in a cluster and thus result in scalability issues.
2. Index recomputation: We assumed that each replica will recompute the index which leads to inefficient usage of resources. Furthermore, index computation is a resource-intensive task with possibly hundreds of stages of pipelined operations.

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