Reserved capacity in DynamoDB - Step-by-Step Execution

Concept Flow - Reserved capacity

Start

↓

Purchase Reserved Capacity

↓

Reserved Capacity Active

↓

Use Reserved Capacity for Read/Write

↓

Billing Applies Discount

↓

Reserved Capacity Period Ends

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End or Renew Reserved Capacity

This flow shows how you buy reserved capacity, use it for your database operations, get billing discounts, and then the reserved period ends or renews.

Execution Sample

DynamoDB

1. Purchase 1000 RCUs for 1 year
2. Use 800 RCUs for reads
3. Use 1200 WCUs for writes
4. Billing applies reserved discount
5. Reserved capacity expires after 1 year

This example traces buying reserved capacity units, using them, and how billing applies discounts during the reserved period.

Execution Table

Step	Action	Reserved Capacity State	Usage	Billing Effect
1	Purchase 1000 RCUs reserved capacity	1000 RCUs reserved active	0 used	No billing yet
2	Use 800 RCUs for reads	1000 RCUs reserved active	800 RCUs used	Usage covered by reserved capacity
3	Use 1200 WCUs for writes	1000 RCUs reserved active	1200 WCUs used	Standard provisioned rates apply for WCUs
4	Billing cycle processes	1000 RCUs reserved active	800 RCUs used, 1200 WCUs used	Discount applied to RCU usage, standard provisioned rates for WCUs
5	Reserved capacity period ends	Reserved capacity expires	Usage continues at standard provisioned rates	No discount after expiration

💡 Reserved capacity period ends, usage billed at standard provisioned rates unless renewed

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5
Reserved RCUs	0	1000 active	1000 active	1000 active	1000 active	0 expired
Used RCUs	0	0	800	800	800	800
Used WCUs	0	0	0	1200	1200	1200
Billing Discount	None	None	Applied to RCUs	Applied to RCUs	Applied to RCUs	None

Key Moments - 2 Insights

Why does usage of WCUs not get a reserved capacity discount in step 3?

Because reserved capacity was only purchased for RCUs, not WCUs. Step 3 shows 1200 WCUs used with no reserved capacity, so billing is at standard provisioned rates.

What happens to reserved capacity after the period ends in step 5?

Reserved capacity expires and no longer applies. Usage after this is billed at standard provisioned rates, as shown in the exit note and step 5.

Visual Quiz - 3 Questions

Look at the execution table, what is the reserved RCUs state after step 2?

A 1000 RCUs reserved active

B 800 RCUs reserved active

C 0 reserved capacity

D Reserved capacity expired

💡 Hint

Check the 'Reserved Capacity State' column at step 2 in the execution table.

At which step does billing start applying discounts for reserved capacity?

A Step 1

B Step 2

C Step 4

D Step 5

💡 Hint

Look at the 'Billing Effect' column in the execution table to see when discounts apply.

If you also purchased 1000 WCUs reserved capacity at step 1, how would billing change at step 3?

A RCUs usage would be billed at standard provisioned rates

B WCUs usage would be covered by reserved capacity discount

C WCUs usage would still be billed at standard provisioned rates

D No billing discount applies at all

💡 Hint

Refer to the 'Usage' and 'Billing Effect' columns in the execution table for step 3.

Concept Snapshot

Reserved Capacity in DynamoDB:
- Buy reserved RCUs or WCUs for a fixed period
- Usage within reserved limits gets billing discounts
- Usage beyond reserved capacity is billed at standard provisioned rates
- Reserved capacity expires after the term
- Renew to continue discounts

Full Transcript

Reserved capacity in DynamoDB means you pay upfront for a set amount of read or write capacity units (RCUs or WCUs) for a period, usually one year. When you use capacity within this reserved amount, your billing is discounted compared to standard provisioned capacity pricing. If you use more than reserved, the extra is billed at standard provisioned capacity rates. After the reserved period ends, the discount no longer applies unless you renew. This example showed purchasing 1000 RCUs reserved capacity, using 800 RCUs and 1200 WCUs, and how billing discounts apply only to the reserved RCUs. It also showed that after the reserved period ends, usage is billed at standard provisioned capacity rates.