Committed use discounts

Committed use discounts (CUDs) for Spanner provide deeply discounted prices in exchange for your commitment to continuously use a certain amount of Spanner compute resources for a year or longer.

Spanner CUDs are ideal when your spending on Spanner compute capacity involves a predictable minimum that you can commit to for at least a year.

Spanner CUD pricing

Spanner CUDs offer two levels of discounts, depending on the commitment period:

  • A one-year CUD gives you a 20 percent discount from the on-demand rate.

  • A three-year CUD gives you a 40 percent discount from the on-demand rate.

When you purchase a CUD, you choose a one- or three-year period, as well as a commitment amount: your expected Spanner expenditure on compute capacity per hour over that period. This commitment amount, after the application of your discount, becomes your commitment fee. You are then billed for this commitment fee on a monthly basis for the duration of the CUD's period. (For a full example, see An example Spanner CUD, below.)

The discount applies to any eligible usage in Spanner projects associated with the Cloud Billing account used to purchase the CUD, regardless of instance configuration or region. All CUDs apply to both regional and multi-region configurations.

Any expenditure beyond the commitment gets billed at the on-demand rate. As your Spanner usage grows, you can purchase additional CUDs to receive discounts on increased expenditures not covered by previous commitments.

If Spanner's on-demand rates change after you purchase a CUD, your commitment fee does not change, and you still receive the same discount percentage on applicable usage.

Resources eligible for Spanner CUDs

Spanner committed use discounts automatically apply to your spending on Spanner compute capacity (as measured in nodes or processing units) across projects. This flexibility helps you achieve a high utilization rate of your commitment across regions and projects without manual intervention, saving you time and money.

Spanner CUDs don't apply to your spending on Spanner storage, backup, or outbound data transfer.

Purchase a Spanner CUD

To purchase or manage Spanner committed use discounts for your Cloud Billing account, you must have a Billing Account Administrator role with that account.

You can purchase a Spanner CUD in the Google Cloud console billing page. Select the Commitments tab, then select the PURCHASE action at the top. Read the Purchasing spend-based commitments section in Google Cloud's documentation for more details.

After purchasing a CUD, the commitment goes into effect within the next hour. Its discounts are automatically applied to subsequent eligible usage.

Please note that, after your purchase a CUD, you cannot cancel its commitment. Make sure the size and duration of your commitment aligns with both your historical and your expected minimum expenditure on Spanner compute capacity.

In addition, before you purchase a commitment, read the Service Specific Terms regarding Committed Units.

An example Spanner CUD scenario

Your commitment should represent your expected minimum hourly expenditure on Spanner compute capacity across your projects over the next one or three years.

As an example, say that you use Spanner instances in two different regions: us-central1, and us-west2. You provision a compute capacity of 10 nodes for an instance in us-central1, and 20 nodes for an instance in us-west2.

From the pricing page, you can calculate the approximate hourly commitment cost:

  • Expenditure in us-central1: 10 nodes * $0.90 per node per hour = $9.00 per hour
  • Expenditure in us-west2: 20 nodes * $1.08 per node per hour = $21.60 per hour
  • Total expenditure across all regions: $9.00 + $21.60 = $30.60 per hour

If you expect to spend that minimum of $30.60 per hour continuously for the next year or more, then you can make a commitment for that amount. In other words, when purchasing that CUD, you would enter "$30.60" as the hourly on-demand commitment amount.

If, on the other hand, you expect to scale down the compute capacity occasionally, you can make a commitment for a lower amount. Any expenditure over that limit is charged at the on-demand rate.

Continuing this example, assume that you do decide on a commitment of $30.60 per hour. As your next step, you choose the length of the commitment's period.

As a basis for comparison, compute the on-demand cost of Spanner compute capacity at the chosen commitment rate, without the application of any commitment discounts:

  • Monthly cost based on on-demand pricing: $30.60 per hour * 730 hours = $22,338 per month

From here, you can calculate the monthly costs and savings you would see under a 1-year CUD, applying its 20% discount, compared to a year of paying the full on-demand rates:

  • Monthly cost of a 1-year, $30.60/hour commitment: ($30.60 per hour - 20% discount) * 730 hours = $17,870.40 per month
  • Total savings per month: $22,338 - $17,870.40 = $4,467.60
  • Total savings with a 1-year, $30.60/hour commitment: $4,467.6 per month * 12 months = $53,611.20

You can apply similar math to calculating the costs and savings of a 3-year CUD, with its 40% discount compared to on-demand rates:

  • Monthly cost of a 3-year, $30.60/hour commitment: ($30.60 per hour - 40% discount) * 730 hours = $13,402.80 per month
  • Total savings per month: $22,338 - $13,402.80 = $8,935.20
  • Total savings with a 3-year, $30.60/hour CUD: $8,935.20 per month * 36 months = $321,667.20

As you can see, a commitment that covers your expected minimum Spanner usage over the years to come can lead to significant savings. Read on for our recommendations on choosing the right CUD size for your Spanner projects.

Recommendations for choosing a commitment

While considering the purchase of Spanner CUDs, keep in mind the following:

  • Regions: Spanner CUDs apply across instance configurations or regions. They apply to both regional and multi-region configurations. If you have Spanner instances in multiple regions, calculate the expenditure across all the regions your projects use while making a commitment.

  • Projects: Determine the consistent baseline expenditure per project while calculating total commitment. Consider that production loads usually run 100% of the time, while development or staging environments may often run intermittently.

  • Instances: If you provision Spanner instances to use a steady level of compute capacity around the clock, consider buying CUDs fully covering their compute resource consumption. However, if you instead frequently scale your instances up or down, consider purchasing CUDs only for their baseline predictable usage.

    If you have instances that you run only for bursts or brief durations, exclude them from your calculations.

Your commitment fee applies to every hour during the term of the commitment, regardless of actual usage. Choose your CUD's commitment amount carefully, based on both your historical Spanner usage and your future expectations. As long as your use of Spanner compute capacity stays above your committed expenditure level, you will enjoy the maximum possible discount for the length of that commitment.

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