Question 1

What does Cosmos DB consulting cover?

Accepted Answer

RU/s sizing + cost optimization (autoscale vs manual vs serverless), multi-API strategy (SQL vs MongoDB vCore vs Cassandra), partition key design (avoid hot partitions, query-pattern alignment), multi-master multi-region topology, five-tier consistency level tuning, Synapse Link for OLTP+analytics, integrated vector search architecture, classic Cosmos MongoDB API → vCore migration scoping. Written architecture documents.

Question 2

RU/s exploding — what's the audit process?

Accepted Answer

Azure Monitor metrics show RU consumption per operation type. Common causes of high RU burn: (a) cross-partition queries (multiplies RU by partition count), (b) full collection scans due to missing index, (c) large response payloads with unnecessary fields, (d) inefficient query patterns hitting non-partition-key filters, (e) autoscale upper bound set too high. We audit the workload and recommend interventions — usually saves 30-60% RU consumption without functional changes.

Question 3

Cosmos MongoDB API (classic) vs vCore — which fits?

Accepted Answer

Classic Cosmos MongoDB API: wire-protocol compatible to MongoDB 4.x, Cosmos DB's native engine underneath, RU/s billing. Good for ~85% of MongoDB patterns. Cosmos for MongoDB vCore (2023+): actual MongoDB engine on Azure, vCore-based billing, much closer to native MongoDB compatibility. For greenfield: vCore is the better fit. For existing classic deployments with working code: stay or migrate based on whether gaps (aggregation operators, change streams) are blocking. We do the gap audit before recommending migration.

Question 4

Multi-master — when does the complexity pay off?

Accepted Answer

Multi-master enables active-active writes across regions with last-writer-wins conflict resolution. Real benefits: write latency for global users (write to local region), region-failure resilience (any region can accept writes). Real costs: 2x+ write RU (every write replicates to every master region), more complex conflict-resolution semantics, application code that handles potential conflicts. We see multi-master earn its complexity for: user-generated content with global users, IoT telemetry from multiple regions, gaming workloads. For most workloads, single-master multi-region is simpler.

Question 5

Consistency level — should I tune away from Session?

Accepted Answer

Session (default) is right for ~90% of workloads — it gives read-your-own-writes within session, eventual everywhere else. Tune away from Session when: (a) Strong consistency is genuinely required (financial, inventory) — accept higher RU cost + cross-region latency, (b) Bounded Staleness — when you can tolerate N versions of staleness for read locality benefits, (c) Eventual — when read latency matters more than consistency (analytics, recommendation feeds). Per-query consistency tuning is powerful but rarely needed beyond the workload-level default.

Question 6

Synapse Link — what does it solve?

Accepted Answer

Synapse Link creates an automatic columnar 'analytical store' alongside the transactional store. Synapse SQL or Spark pools can query analytical store without impacting OLTP RU/s. Use cases: real-time analytics over transactional data without ETL, cost-effective historical analytics (analytical store is much cheaper than transactional RU/s), eliminating Cosmos → ADLS → Synapse pipelines. Limitations: analytical store has 2-minute lag, not all queries optimal, no transactional consistency with OLTP store. We help decide if Synapse Link fits your analytics architecture.

Question 7

Does consulting include migration execution?

Accepted Answer

No — execution lives on dedicated engagements. Consulting is the decision phase: audit RU/s, design multi-API strategy, model multi-master tradeoffs, tune consistency levels, plan Synapse Link / vector search adoption, scope migrations. Execution covers RU/s optimization deployment, classic MongoDB API → vCore migration, Cosmos → MongoDB Atlas migration, multi-master rollout. The split keeps consulting deliverables crisp.

Azure Cosmos DB Consulting

What our Cosmos DB consulting covers

Cosmos DB consulting — common questions

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