In Cosmos DB, what does the choice of PARTITION KEY most directly determine?
A.How items distribute across physical partitions — affecting scalability and query efficiency
Distribution + query targeting = partition key role. Correct.
B.The encryption used at rest
Encryption is platform-managed — unrelated.
C.Which consistency level applies
Consistency is account/request-level config.
D.The document schema
Items remain schemaless regardless of key choice.
Why this answer
Partition key value routes each item to a logical partition — good keys spread load evenly (high cardinality) and keep query targets single-partition. Poor keys create hot partitions and expensive cross-partition fan-out queries.
Correct answer: A · Last reviewed 2026-11-05
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