C100DBA Application Administration Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✗

  { w: 2, j: true }

  Why it's wrong here

  This write concern requires acknowledgment from the primary and one secondary and waits for journaling on those nodes. However, it does not guarantee that a majority of voting members have acknowledged the write. For example, in a three-node replica set, w:2 is a majority, but in a five-node set, it is not. Since the requirement is for majority acknowledgment, this is not always correct.

• ✗

  { w: 1, j: true }

  Why it's wrong here

  This write concern acknowledges the write on the primary and waits for it to be journaled on the primary only. It does not ensure that a majority of replica set members have the write, so it cannot prevent rollback if the primary fails. Therefore, it does not meet the requirement for majority acknowledgment.

• ✓

  { w: "majority", j: true }

  Why this is correct

  This write concern combines majority acknowledgment with journaling. The w: "majority" ensures that a majority of replica set members have applied the write, and j: true ensures that the write is committed to the on-disk journal on those members. This provides the highest level of durability and meets the developer's requirement.

• ✗

  { w: "majority", j: false }

  Why it's wrong here

  This write concern ensures majority acknowledgment but does not wait for the write to be journaled. Without journaling, the write could be lost if the primary crashes before the journal is written to disk, even though it was acknowledged by a majority. The developer specifically requires journaling, so this is insufficient.