How many points do the three occupied memories consume, and how much budget remains?

5 from 8 Points; remain 3 Points.

The team also wants to turn on the analysis memory. What does the budget show?

With 3 Other points would be 8 from 8The budget is exhausted, and the need is only suspected.

Should the store outsource sessions to its own key-value store? How do you weigh up?

It would be appropriate for this access, but the relational database carries sessions today. Without a proven need, it costs 2 Points of operation; recommendation: not at first.

ApproachChapter II · Data · Building block 8 of 9

Polyglot Persistence

Polyglot Persistence uses multiple storage technologies for different data needs. Each additional technology increases operational and synchronization effort.

By Michael Meierhoff · Meierhoff Systems

Relevant sourceThere the binding status applies.
Derived memoryIt is filled from the source.
Operating costsEvery store needs care.

Context

Why this is important

Several memories are only worthwhile with a clear task and a clear authoritative source, because each memory costs operation. Which model fits an access shows SQL & NoSQL; this is about the combination and its price.

This building block explains the combined use of different memories. For the selection of a single model, see SQL & NoSQL.

At a glance · Every service, suitable memory

Each service selects the type of storage that matches its data and queries: relational, document, or search index.

Shop example · Complexity budget

What storage does the shop carry?

Variant: The grown shop keeps orders relational, searches for products in a search index and stores product images in an object memory. The shop remains technically modular.

This is how you read the picture

Relevant source The relational database for orders and status.
Derived memory The search index is derived from the catalogue.
Operating costs The points per memory against the capacity of 8.

5 of 8 PointsWhat the small team can do reliably

Still 3 Points Free. Everything that is spent is documented.

Values illustrative

Turn on memory and see if the operating budget is enough; the points are illustrative.

Benefits & limitations

Helps if:

Different access patterns can use a suitable storage model for each data area.
A derived view complements the authoritative source for specialised access patterns poorly served by its data model.
A team with capacity for additional operation and reconciliation can responsibly connect multiple storage facilities.

Boundaries

Every additional store needs installation, monitoring, backups, updates and team expertise.
Derived data must be reconcilable and rebuildable from the source when necessary.
There is no common transaction across multiple stores; coordinated flows require a Saga.

In practice

Assign each store a clear purpose, a binding source, and a responsible team. Determine which data is only derived or cached.
Define reconciliation, failure handling and rebuilding between stores. Compare control values so a projection can be trusted again after a failure.
Weigh operational and consistency management costs against measured benefits. SQL & NoSQL compares storage types; Data Ownership clarifies authoritative ownership.

Read the detailed explanation

Polyglot Persistence combines stores with different data models and access characteristics. Each store has a bounded purpose, an owner and its own operational procedures. An explicit authoritative source defines where changes are accepted.

Search indexes, caches and other projections can be derived from that source. Synchronisation may lag and must handle failures and rebuilding. Every additional store adds backup, monitoring, on-call and consistency management work.

Persistence covers selecting the primary store; Data Ownership establishes which source has authority to accept changes.

Check your understanding

Test yourself in three stages

ReadingCheck in the picture
How many points do the three occupied memories consume, and how much budget remains?
View the solution with justification
5 from 8 Points; remain 3 Points.
ApplyingTransferred to a new situation
The team also wants to turn on the analysis memory. What does the budget show?
View the solution with justification
With 3 Other points would be 8 from 8The budget is exhausted, and the need is only suspected.
EvaluateWeighing an alternative
Should the store outsource sessions to its own key-value store? How do you weigh up?
View the solution with justification
It would be appropriate for this access, but the relational database carries sessions today. Without a proven need, it costs 2 Points of operation; recommendation: not at first.

Explore further

These building blocks continue the thoughts of this page.

References

Continue on the learning path

Next in Data & state: Saga.

9 Building blocks

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