coalestra 0.5.3

Integration-ready consistent snapshots with required/optional resources, bounded batch dispatch, precise deadlines, and fast local sources.

Coalestra

Coalestra is a dependency-free Python library for building consistent operational snapshots from prioritized read-only sources.

It coalesces duplicate requests, batches compatible resources, derives values from existing resources, bounds read concurrency, isolates failing source partitions, and accepts event-driven updates directly into its cache. The core is domain-agnostic and contains no knowledge of HTTP, SQL, Redis, Binance, trading, or Alphora.

Capabilities

• Immutable snapshots with provenance and freshness metadata.
• Single-stage builds and incremental multi-stage SnapshotSession workflows.
• Per-key single-flight coalescing across overlapping requests.
• Single-resource, batch, and derived source contracts in one priority chain.
• Recursive dependencies, dependency sharing, and cycle detection.
• Builder-wide concurrency limits shared by all builds and sessions.
• Optional per-source concurrency limits.
• Source-specific retry and circuit-breaker policies.
• Circuit isolation by source, namespace, subject, or full resource.
• Case-preserving resource identity with configurable normalization and qualifiers.
• Batch cache reads/writes, bounded LRU storage, pruning, invalidation, and cache statistics.
• Per-resource TTL, stale windows, stale-on-error fallback, and background refresh modes.
• Direct asynchronous and synchronous event publication into the cache.
• Monotonic publication that rejects older or duplicate events by default.
• Consolidated immutable diagnostics on every snapshot.
• Buffered event and metrics sinks that keep downstream I/O outside the acquisition path.
• Replaceable cache, clock, event, and metrics interfaces.
• Async API plus persistent synchronous facades.
• Required/optional resource requests for integration-safe partial snapshots.
• Deadline-aware retries, bounded batch chunking, and future-timestamp validation.
• Health snapshots for cache, circuits, capacity, refreshes, and in-flight work.
• Fast inline execution for explicitly non-blocking local synchronous sources.
• Strict static typing and no runtime dependencies.

Installation

python -m pip install -e ".[dev]"

Python 3.10 or newer is supported.

Integration-ready requests

Use SnapshotRequest to separate resources that must exist from resources that may fail without aborting the unit of work:

from coalestra import SnapshotRequest

request = SnapshotRequest(
    required=[ACCOUNT, ALL_POSITIONS],
    optional=[MARKET_HEALTH, LEARNING_CONTEXT],
)

snapshot = await builder.build_request(request, deadline_seconds=3.0)

Only required failures raise SnapshotBuildError. The exception exposes a partial snapshot, so already resolved values and diagnostics are not lost. Sessions and synchronous facades expose the same request API.

Fast local sources and bounded batches

Synchronous adapters run in worker threads by default. Lock-protected, non-blocking in-memory reads can opt into inline execution:

local_source = CallableBatchSource(
    name="market-state",
    priority=100,
    supports=supports_market,
    fetcher=read_local_market_state,
    run_sync_in_thread=False,
    max_batch_size=100,
)

Do not use inline execution for network, filesystem, database, or any potentially blocking operation. Large batches are split into capacity-aware waves, avoiding unbounded task creation.

Timestamp precision

ObservationPolicy rejects observations too far in the future, preventing clock errors from making values artificially fresh. Small accepted clock differences are recorded as clock_skew_seconds metadata.

Generic resource identity

ResourceKey preserves case by default, trims surrounding whitespace and supports immutable qualifiers:

from coalestra import ResourceKey

candles = ResourceKey(
    "market",
    "candles",
    "BTCUSDT",
    {"interval": "1m", "limit": 500},
)

assert candles.qualifier("interval") == "1m"

Qualifiers are normalized into a sorted tuple, so mapping insertion order does not affect equality or hashing. Systems with case-insensitive identity can opt in to a normalizer:

from coalestra import CASE_INSENSITIVE_KEY_NORMALIZER, ResourceKey

key = ResourceKey(
    "Tenant-A",
    "DocumentId",
    "/Path/File",
    normalizer=CASE_INSENSITIVE_KEY_NORMALIZER,
)

LEGACY_KEY_NORMALIZER and ResourceKey.legacy(...) reproduce Coalestra 0.1-0.3 behavior.

Batch cache operations and refresh policies

AsyncMemoryCache performs multi-key reads and writes under one lock, defaults to a bounded 10,000-entry LRU, removes fully expired entries on access, and exposes statistics and namespace invalidation. Custom caches may implement BatchAsyncCache; older single-key caches remain supported.

Freshness policies support three refresh modes:

from coalestra import FreshnessPolicy, RefreshMode

policy = FreshnessPolicy(
    ttl_seconds=5.0,
    max_stale_seconds=30.0,
    refresh_mode=RefreshMode.STALE_WHILE_REVALIDATE,
)

• BLOCKING: wait for a fresh source when the cache is outside TTL.
• STALE_WHILE_REVALIDATE: return an acceptable stale value and refresh it in the background.
• REFRESH_AHEAD: return a fresh value and refresh it before TTL expiry.

Long-lived asynchronous applications can call await builder.wait_for_refreshes(). SyncSnapshotBuilder.close() waits for pending refreshes before stopping its event loop.

Payload isolation

Coalestra deep-copies payload values and nested metadata when data crosses ownership boundaries. Source results, cache entries, publisher results, derived dependency snapshots, single-flight callers, and session snapshots therefore do not share mutable payload objects by default. Mutating one returned snapshot cannot modify the cache or another snapshot.

Payloads must support copy.deepcopy. A payload that cannot be copied is reported as a structured PayloadIsolationError instead of being stored by reference. Integrations that use proven immutable values or specialized model-copying APIs may provide a custom copier:

from coalestra import SnapshotBuilder

builder = SnapshotBuilder(
    sources,
    payload_copier=lambda value: value.model_copy(deep=True),
)

AsyncMemoryCache and standalone ResourcePublisher instances accept the same payload_copier option. Returning the original object from a custom copier is safe only when the payload is deeply immutable.

Snapshot diagnostics

Every snapshot contains immutable acquisition diagnostics:

snapshot = await builder.build(keys)
print(snapshot.diagnostics.cache_hits)
print(snapshot.diagnostics.source_calls_by_source)
print(snapshot.diagnostics.observation_skew_ms)

Diagnostics include requested, resolved and failed resource counts; cache hits/misses and batch operations; stale values and coalesced requests; source, batch and derived calls; refresh outcomes; per-source latency totals; total duration; and observation-time skew.

Buffered observability

Wrap a potentially slow sink so logging or metrics export does not run on the acquisition path:

from coalestra import BufferedEventSink, BufferedMetricsSink

events = BufferedEventSink(file_event_sink, max_pending=10_000)
metrics = BufferedMetricsSink(prometheus_adapter, max_pending=10_000)

builder = SnapshotBuilder(sources, events=events, metrics=metrics)

# During shutdown
events.close()
metrics.close()

The default overflow policy drops the oldest queued record. DROP_NEWEST and RAISE are also available. Delivery failures are counted and never injected into resource resolution.

Minimal build

import asyncio

from coalestra import CallableSource, ResourceKey, SnapshotBuilder

PRICE = ResourceKey("market", "price", "BTCUSDT")

builder = SnapshotBuilder(
    [
        CallableSource(
            name="rest",
            priority=10,
            supports=lambda key: key == PRICE,
            fetcher=lambda _key, _context: {"price": "65000.00"},
        )
    ]
)

snapshot = asyncio.run(builder.build([PRICE]))
print(snapshot.value(PRICE, dict))

Batch sources

A batch source receives every unresolved compatible key available at its priority level. It may return a partial mapping; omitted resources continue through lower-priority sources.

from coalestra import CallableBatchSource

async def fetch_prices(keys, _context):
    symbols = [key.subject for key in keys]
    response = await remote_api.fetch_prices(symbols)
    return {key: response[key.subject] for key in keys if key.subject in response}

price_source = CallableBatchSource(
    name="price-api",
    priority=100,
    supports=lambda key: key.namespace == "market" and key.name == "price",
    fetcher=fetch_prices,
)

Incremental sessions

A session keeps one identity, creation time, deadline, and pinned-value memo across multiple stages. Read capacity is controlled by the long-lived builder and is therefore shared with every other active build and session.

async with builder.session(
    snapshot_id="cycle-42",
    deadline_seconds=3.0,
    metadata={"tenant": "example"},
) as session:
    baseline = await session.resolve(baseline_keys, strict=False)
    selected = choose_resources_from(baseline)
    final = await session.resolve(selected, strict=False)

Successful values remain pinned inside the session. Existing errors can be retried explicitly:

await session.resolve([KEY], retry_errors=True)

Derived resources

Derived sources declare dependencies and calculate a resource from an immutable dependency snapshot.

from coalestra import CallableDerivedSource, ResourceKey

EXCHANGE_INFO = ResourceKey("exchange", "info")

rules_source = CallableDerivedSource(
    name="symbol-rules",
    priority=100,
    supports=lambda key: key.namespace == "exchange" and key.name == "rules",
    dependencies=lambda _key: (EXCHANGE_INFO,),
    deriver=lambda key, snapshot, _context: extract_rules(
        snapshot.value(EXCHANGE_INFO, dict),
        key.subject,
    ),
)

Dependencies may themselves be cached, batched, fetched, or derived. Direct and indirect cycles are rejected.

Every SnapshotValue carries an opaque resource version. Derived values record the versions used for each dependency. A cached derived value is accepted only while every recorded dependency version is still current. Publishing or caching a newer dependency therefore invalidates affected derived values lazily on their next read, including transitive derived chains.

Global and per-source capacity

max_concurrency is a builder-wide limit. Concurrent calls to build() and multiple active sessions share the same capacity.

builder = SnapshotBuilder(
    sources,
    max_concurrency=12,
    source_concurrency={
        "remote-rest": 4,
        "database": 6,
    },
)

Callable adapters can also declare their own limit:

rest_source = CallableSource(
    name="remote-rest",
    priority=10,
    supports=supports_rest,
    fetcher=fetch_rest,
    max_concurrency=4,
)

An explicit source_concurrency entry overrides the limit declared by the source. Batch calls consume one slot regardless of batch size. Derivation consumes a slot only while the derivation function itself runs; dependency acquisition uses its own source slots.

Source-specific resilience and circuit scopes

from coalestra import (
    CircuitBreakerPolicy,
    CircuitScope,
    RetryPolicy,
    SourceResiliencePolicy,
)

stream_policy = SourceResiliencePolicy(
    retry=RetryPolicy(max_attempts=1),
    circuit=CircuitBreakerPolicy(
        scope=CircuitScope.SUBJECT,
        failure_threshold=2,
        recovery_timeout_seconds=5.0,
    ),
)

stream_source = CallableSource(
    name="market-stream",
    priority=100,
    supports=supports_market,
    fetcher=read_stream_state,
    resilience_policy=stream_policy,
)

Available scopes:

• SOURCE: one circuit for the complete source;
• NAMESPACE: one circuit per source and resource namespace;
• SUBJECT: one circuit per source and subject;
• RESOURCE: one circuit per complete ResourceKey.

A stale payload is treated as an unsuccessful circuit outcome for its configured scope. With SUBJECT, stale data for one symbol does not disable the source for other symbols.

Policies can also be supplied centrally through source_resilience or a ResiliencePolicyResolver.

Direct event publication

A long-lived builder exposes a ResourcePublisher backed by the same cache used by snapshot acquisition.

await builder.publisher.publish(
    PRICE,
    {"price": "65001.25"},
    source="market-stream",
    observed_at=event_timestamp,
    metadata={"sequence": sequence},
)

Publication is monotonic by default:

• an older observed_at is ignored;
• an equal timestamp is treated as a duplicate;
• force=True permits explicit reconciliation or repair;
• replace_equal=True permits replacement at the same timestamp.

Several updates can be published together:

from coalestra import ResourceUpdate

await builder.publisher.publish_many(
    [
        ResourceUpdate(PRICE_BTC, btc, source="stream", observed_at=btc_time),
        ResourceUpdate(PRICE_ETH, eth, source="stream", observed_at=eth_time),
    ]
)

Uncertain state can be invalidated:

await builder.publisher.invalidate(POSITION_BTC, reason="stream-gap")

A session intentionally keeps values already pinned before a publication. New builds and new sessions observe the published value.

Synchronous applications

SyncSnapshotBuilder owns one persistent event-loop thread. Keep it alive for the application lifetime.

from coalestra import SyncSnapshotBuilder

with SyncSnapshotBuilder(builder) as sync_builder:
    sync_builder.publisher.publish(
        PRICE,
        {"price": "65001.25"},
        source="market-stream",
    )

    # Suitable for callbacks that should not block their producer thread.
    future = sync_builder.publisher.submit_publish(
        POSITION,
        position,
        source="user-stream",
        observed_at=event_timestamp,
    )

    snapshot = sync_builder.build([PRICE, POSITION])
    future.result()

Synchronous fetchers and derivation functions run in worker threads by default. run_sync_in_thread=False is available only for guaranteed non-blocking local reads. Transport-level timeouts remain necessary because an already-running Python thread cannot be forcibly terminated. Closing the synchronous facade closes its underlying builder by default.

Architectural boundary

Coalestra owns read acquisition, cache publication, freshness, coalescing, fallback, derivation, and read concurrency. The consuming application owns business decisions, authorization, risk, writes, transactions, and domain validation.

Project layout

src/coalestra/
├── adapters/         # Callable single, batch, and derived sources
├── cache/            # Cache implementations and event publisher
├── concurrency/      # Builder-wide and per-source capacity control
├── core/             # Models, protocols, and errors
├── observability/    # Event and metrics sinks
├── orchestration/    # Builder, session, policy, and single-flight
├── resilience/       # Retry, circuit policies, and circuit breaker
└── sync.py           # Persistent synchronous facades

Quality pipeline

make quality

This runs formatting, linting, strict mypy, verifies the 500-test minimum, executes the full 618-test suite, and builds the package.

Documentation

• Architecture
• Public API
• Migration from 0.4
• Revisão final para integração
• Integração com o Alphora
• Changelog

License

MIT