DCB Store

The dcb/ package provides the event storage layer. It implements Dynamic Consistency Boundaries on top of FoundationDB.

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What DCB Solves

Traditional event stores fix consistency at the stream level. One stream = one aggregate = one lock.

DCB removes this constraint. Consistency boundaries emerge from what each command actually reads.

Learn more: Dynamic consistency →

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The Interface

type DcbStore interface {
    Append(ctx context.Context, events []Event, condition *AppendCondition) error
    Read(ctx context.Context, query Query, opts *ReadOptions) iter.Seq2[StoredEvent, error]
    ReadAll(ctx context.Context) iter.Seq2[StoredEvent, error]
    Database() fdb.Database
    Namespace() string
}

Method	Purpose
Append	Write events, optionally with conditional guard
Read	Stream events matching a query
ReadAll	Stream all events in namespace

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Creating a Store

import (
    "github.com/apple/foundationdb/bindings/go/src/fdb"
    "github.com/err0r500/fairway/dcb"
)

fdb.MustAPIVersion(740)
db := fdb.MustOpenDefault()
store := dcb.NewDcbStore(db, "myapp")

With Observability

store := dcb.NewDcbStore(db, "myapp",
    dcb.StoreOptions{}.WithLogger(myLogger),
    dcb.StoreOptions{}.WithMetrics(myMetrics),
)

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Sections

• Interface & Types — Event, Versionstamp, StoredEvent
• Append Conditions — conditional writes, conflict detection
• Storage Layout — how events are indexed in FDB
• Streaming Reads — k-way merge for memory-efficient reads

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Errors

Error	Meaning
ErrEmptyEvents	Append called with empty slice
ErrAppendConditionFailed	Condition violated — retry
ErrInvalidQuery	QueryItem has neither types nor tags