Which of the following best distinguishes read repair from anti-entropy repair in Cassandra?

Question

BlackTom AI · Accepted Answer

Question restatement: Which of the following best distinguishes read repair from anti-entropy repair in Cassandra?
Option 1: Read repair is a manual process triggered by the administrator, while anti-entropy repair happens automatically during each read operation.
-Analysis: This is inaccurate. Read repair is not a manual process; it is an automatic process that can occur during reads at read time, but anti-entropy repair is not tied to every read operation. It is typically run as a separate, maintenance-oriented repair process initiated by the user or administrator (e.g., via nodetool repair). The statement mischaracterizes both the automation and trigger mechanisms of the two repairs.

Option 2: Read repair synchronizes only data actively read by clients, while anti-entropy repair performs a full data comparison between replicas to fix inconsistencies.
-Analysis: This is correct. Read repair focuses on correcting inconsistencies for the data items involved in the current read path, effectively touching only the data that was read by the query. Anti-entropy repair (often called repair) compares data across replicas (using Merkle trees) to identify and fix divergences, potentially covering broader data ranges beyond what a single read touches. This option aligns with Cassandra’s distinction between on-demand, read-path repair vs. full-data-range, background synchronization.

Option 3: Read repair uses Merkle trees for comparison, while anti-entropy repair relies on read-time timestamps.
-Analysis: This is inaccurate. Merkle trees are central to anti-entropy repair, not to read repair. Read repair does not typically rely on Merkle-based comparisons during the read; it corrects inconsistencies observed in the read results. The statement reverses the roles of the two mechanisms.

Option 4: Read repair is used only in eventual consistency mode, while anti-entropy repair is used in strong consistency mode.
-Analysis: This is false. Cassandra’s repair mechanisms are not exclusive to consistency levels in that way. Read repair can occur under various consistency levels, and anti-entropy repair is a maintenance operation independent of a specific consistency mode. The claim about strict mode usage is a misconception.

Which of the following best distinguishes read repair from anti-entropy repair in Cassandra? 单项选择题

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