In a sharded replica set environment, the w Option provides ability for write concern and j Option provides ability for the data to be written on disk journal. Consider that we have a seven member…

Question

Options

• A1
• B2
• C0
• D7

• A
  15% (6)
• B
  74% (29)
• C
  8% (3)
• D
  3% (1)

Explanation

Option B (2) is correct because in a 7-member sharded replica set, setting the write concern j to 2 means MongoDB requires at least 2 members (typically the primary plus one secondary) to acknowledge that the write has been committed to the on-disk journal before confirming success - this ensures durable writes survive a single-node failure.

Why the distractors are wrong:

• A (1): Requiring only 1 member to journal-acknowledge (the primary alone) offers no protection if the primary crashes immediately after - data could be lost on failover.
• C (0): Setting j: 0 disables journal acknowledgment entirely, meaning MongoDB doesn't wait for the write to persist to disk - maximum risk of data loss on crash.
• D (7): Requiring all 7 members to journal-acknowledge before confirming the write is impractical - it maximizes durability but cripples write throughput and introduces high latency.

Memory tip: Think of j like a "witness count" - you need at least 2 witnesses (primary + 1 secondary) to ensure a write is safely journaled beyond a single point of failure. In replica set write concern, 1 = risky, 2 = safe minimum, all = overkill.

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