SQL and databases

Platform · SQL

Platform concern — Make persistence predictable under concurrency, retries, migrations, and partial failure.

A query boundary with transaction ownership, pool limits, migration discipline, and safe errors.

Key concepts

Pool

Finite connections

Transaction

Atomic unit

Migration

Compatible step

Operating model

Decisions to make before production

Decision	Recommended posture	Failure it prevents
Pool	Finite connections	Protect the database from application concurrency.
Transaction	Atomic unit	Make partial writes impossible where required.
Migration	Compatible step	Allow old and new versions to coexist.

Boundary and failure behavior

Database behavior dominates many heavy workloads; correctness and saturation matter before query micro-optimizations.

Questions for review

Question	Answer to document
What belongs in a transaction?	State changes that must share one commit decision.
What should be retried?	Transient, idempotent operations with clear transaction semantics.
How should pool pressure appear?	As a metric and alert before requests fail en masse.

Implementation notes

Engineering move	Guidance
Define the unit of work	Decide which writes commit together and which can be asynchronous.
Parameterize queries	Keep values separate from SQL text and validate sort or filter choices.
Bound the pool	Match concurrency to database capacity, not to request volume.
Plan migrations	Use expand, migrate, contract when old and new code overlap.

Decision lens

Mode	Practical emphasis
Read path	Index for real predicates and measure result size.
Write path	Use transactions and idempotency for repeated delivery.
Migration	Keep compatibility during rolling deploys and backfills.

layer-group · Add cache and jobs — Read the focused guide for this boundary.
arrows-rotate · Evolve schemas — Read the focused guide for this boundary.
gauge-high · Measure persistence — Read the focused guide for this boundary.

References

Last modified on September 10, 2026

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SQL and databases

SQL and databases

Platform · SQL

Key concepts

Pool

Transaction

Migration

Operating model

Decisions to make before production

Boundary and failure behavior

Questions for review

Implementation notes

Decision lens

References

​SQL and databases

​Platform · SQL

​Key concepts

Pool

Transaction

Migration

​Operating model

​Decisions to make before production

​Boundary and failure behavior

​Questions for review

​Implementation notes

​Decision lens

​Related topics

​References

SQL and databases

Platform · SQL

Key concepts

Operating model

Decisions to make before production

Boundary and failure behavior

Questions for review

Implementation notes

Decision lens

Related topics

References