feat(postgres): add PostgreSQL event store implementation #169

2025-12-03T13:57:46-08:00

jwilger commented

2025-12-03 13:57:46 -08:00

(Migrated from github.com)

Summary

Add eventcore-postgres crate with sqlx-backed EventStore implementation
Implement PostgreSQL migrations for events table with database-side version management trigger
Add configurable connection pool settings (max connections, acquire timeout)
Integrate tracing instrumentation for read_stream and append_events operations
Support atomic multi-stream commits with optimistic concurrency control

Changes

New crate: eventcore-postgres with PostgresEventStore implementing the EventStore trait
Migrations: Schema includes eventcore_events table with trigger-based version assignment
Concurrency: Session-config-based expected version validation for multi-stream atomicity
Configuration: PostgresConfig for pool tuning, plus from_pool() for shared pool scenarios
CI: Add Postgres service to test matrix (PG 15-18) and mutation testing job

Test plan

Contract test suite passes against PostgreSQL store
Concurrent conflict detection and retry scenario covered
Atomic multi-stream commit verification with transaction isolation
Observability test confirms tracing spans emitted
Mutation testing passes (all viable mutants caught)

## Summary - Add `eventcore-postgres` crate with sqlx-backed EventStore implementation - Implement PostgreSQL migrations for events table with database-side version management trigger - Add configurable connection pool settings (max connections, acquire timeout) - Integrate tracing instrumentation for read_stream and append_events operations - Support atomic multi-stream commits with optimistic concurrency control ## Changes - **New crate**: `eventcore-postgres` with `PostgresEventStore` implementing the `EventStore` trait - **Migrations**: Schema includes `eventcore_events` table with trigger-based version assignment - **Concurrency**: Session-config-based expected version validation for multi-stream atomicity - **Configuration**: `PostgresConfig` for pool tuning, plus `from_pool()` for shared pool scenarios - **CI**: Add Postgres service to test matrix (PG 15-18) and mutation testing job ## Test plan - [x] Contract test suite passes against PostgreSQL store - [x] Concurrent conflict detection and retry scenario covered - [x] Atomic multi-stream commit verification with transaction isolation - [x] Observability test confirms tracing spans emitted - [x] Mutation testing passes (all viable mutants caught)

copilot-pull-request-reviewer[bot] (Migrated from github.com) reviewed

2025-12-03 14:00:12 -08:00

copilot-pull-request-reviewer[bot] (Migrated from github.com) left a comment

Pull request overview

This PR adds a production-ready PostgreSQL adapter for EventCore with comprehensive error handling and serialization support. It introduces the eventcore-postgres crate implementing the EventStore trait, adds serialization requirements to the Event trait, and refactors the storage layer to support JSON serialization of events.

Key Changes

Added serialization bounds (Serialize + DeserializeOwned) to the Event trait to enable persistence
Refactored StreamWrites to capture event data and metadata at append time for adapters
Implemented PostgreSQL adapter with ACID transactions, optimistic concurrency, and SQLSTATE error mapping

Reviewed changes

Copilot reviewed 30 out of 31 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/command.rs	Added serialization trait bounds to Event trait
src/store.rs	Refactored StreamWrites to capture event data, added StreamId serialization, new error variants
src/lib.rs	Exported StreamWriteEntry for adapter use
eventcore-postgres/src/lib.rs	PostgreSQL EventStore implementation with connection pooling, migrations, and error mapping
eventcore-postgres/migrations/*.sql	Database schema with unique constraints for optimistic concurrency
eventcore-postgres/tests/*.rs	Integration tests for connection, concurrency, atomicity, observability, migrations, and contract compliance
tests/*.rs	Added Serialize/Deserialize to all test event types
Cargo.toml	Added eventcore-postgres to workspace and serde_json dependency
docs/manual/07-operations/01-deployment-strategies.md	Added metadata column migration guide

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## Pull request overview This PR adds a production-ready PostgreSQL adapter for EventCore with comprehensive error handling and serialization support. It introduces the `eventcore-postgres` crate implementing the `EventStore` trait, adds serialization requirements to the `Event` trait, and refactors the storage layer to support JSON serialization of events. ### Key Changes - Added serialization bounds (`Serialize + DeserializeOwned`) to the `Event` trait to enable persistence - Refactored `StreamWrites` to capture event data and metadata at append time for adapters - Implemented PostgreSQL adapter with ACID transactions, optimistic concurrency, and SQLSTATE error mapping ### Reviewed changes Copilot reviewed 30 out of 31 changed files in this pull request and generated 2 comments. <details> <summary>Show a summary per file</summary> | File | Description | | ---- | ----------- | | src/command.rs | Added serialization trait bounds to Event trait | | src/store.rs | Refactored StreamWrites to capture event data, added StreamId serialization, new error variants | | src/lib.rs | Exported StreamWriteEntry for adapter use | | eventcore-postgres/src/lib.rs | PostgreSQL EventStore implementation with connection pooling, migrations, and error mapping | | eventcore-postgres/migrations/*.sql | Database schema with unique constraints for optimistic concurrency | | eventcore-postgres/tests/*.rs | Integration tests for connection, concurrency, atomicity, observability, migrations, and contract compliance | | tests/*.rs | Added Serialize/Deserialize to all test event types | | Cargo.toml | Added eventcore-postgres to workspace and serde_json dependency | | docs/manual/07-operations/01-deployment-strategies.md | Added metadata column migration guide | </details> --- 💡 <a href="/jwilger/eventcore/new/main/.github/instructions?filename=*.instructions.md" class="Link--inTextBlock" target="_blank" rel="noopener noreferrer">Add Copilot custom instructions</a> for smarter, more guided reviews. <a href="https://docs.github.com/en/copilot/customizing-copilot/adding-repository-custom-instructions-for-github-copilot" class="Link--inTextBlock" target="_blank" rel="noopener noreferrer">Learn how to get started</a>.

eventcore-postgres/tests/i011_observability_test.rs

					
				@ -0,0 +71,4 @@

				    // Then: Tracing spans are emitted for both append and read operations

				    assert!(

				        logs_contain("postgres.append_events") && logs_contain("postgres.read_stream"),

The function logs_contain is called but not defined. The tracing-test crate provides a logs_contain! macro, not a function. Change to logs_contain!("postgres.append_events") && logs_contain!("postgres.read_stream").

        logs_contain!("postgres.append_events") && logs_contain!("postgres.read_stream"),

The function `logs_contain` is called but not defined. The `tracing-test` crate provides a `logs_contain!` macro, not a function. Change to `logs_contain!("postgres.append_events") && logs_contain!("postgres.read_stream")`. ```suggestion logs_contain!("postgres.append_events") && logs_contain!("postgres.read_stream"), ```

eventcore-postgres/tests/i013_concurrency_retry_test.rs

					
				@ -0,0 +119,4 @@

				        .as_ref()

				        .map(|reader| reader.len())

				        .unwrap_or_default();

				    let logs_contain_conflict = logs_contain("postgres.version_conflict");

The function logs_contain is called but not defined in the test file. The tracing-test crate provides a logs_contain macro, not a function. The correct usage should be logs_contain!("postgres.version_conflict") instead of logs_contain("postgres.version_conflict").

    let logs_contain_conflict = logs_contain!("postgres.version_conflict");

The function `logs_contain` is called but not defined in the test file. The `tracing-test` crate provides a `logs_contain` macro, not a function. The correct usage should be `logs_contain!("postgres.version_conflict")` instead of `logs_contain("postgres.version_conflict")`. ```suggestion let logs_contain_conflict = logs_contain!("postgres.version_conflict"); ```

jwilger (Migrated from github.com) reviewed

2025-12-03 15:09:43 -08:00

jwilger (Migrated from github.com) left a comment

Several issues need to be addressed.

.config/nextest.toml

Why? Any way to not put this limitation in place?

Why? Any way to *not* put this limitation in place?

.github/workflows/ci.yml

					
				@ -64,14 +64,12 @@ jobs:

				      - name: Run tests

				        env:

Can we maybe pick one and normalize?

docs/manual/07-operations/01-deployment-strategies.md

There are no "existing deployments" and we don't worry about backward compatibility for versions < 1.0.0

eventcore-postgres/src/lib.rs

					
				@ -0,0 +1,335 @@

				use std::time::Duration;

Magic numbers for things that should ideally be configurable.

Yuck?

eventcore-postgres/src/lib.rs

					
				@ -0,0 +119,4 @@

				                }

				            })?;

				            events.push(event);

				        }

How many events would need to be on a stream before just selecting the whole set at once (vs. streaming) becomes a problem?

eventcore-postgres/src/lib.rs

					
				@ -0,0 +193,4 @@

				        Ok(EventStreamSlice)

				    }

				}

Wouldn't it be much cleaner to do an atomic insert where we insert all events in one statement along with a condition that the stream versions for each stream match the expected values, so that we only need to execute a single statement without locks?

src/store.rs

					
				@ -190,1 +219,3 @@

				    derive(Debug, Clone, PartialEq, Eq, Hash, AsRef, Deref, Display)

				    derive(

				        Debug,

				        Clone,

Any particular reason we can't use derives with serde here?

jwilger (Migrated from github.com) reviewed

2025-12-03 15:13:51 -08:00

.github/workflows/ci.yml

					
				@ -64,14 +64,12 @@ jobs:

				      - name: Run tests

				        env:

Normalized to DATABASE_URL which is the standard convention used by sqlx and other database tools. Removed the custom EVENTCORE_TEST_POSTGRES_URL and TEST_DATABASE_URL env vars from CI. Commit: c0ccf9e

Normalized to `DATABASE_URL` which is the standard convention used by sqlx and other database tools. Removed the custom `EVENTCORE_TEST_POSTGRES_URL` and `TEST_DATABASE_URL` env vars from CI. Commit: c0ccf9e

jwilger (Migrated from github.com) reviewed

2025-12-03 15:14:43 -08:00

docs/manual/07-operations/01-deployment-strategies.md

Removed the pre-1.0 migration upgrade guide section. Commit: 2e21fa9

Removed the pre-1.0 migration upgrade guide section. Commit: 2e21fa9

jwilger (Migrated from github.com) reviewed

2025-12-03 15:16:43 -08:00

eventcore-postgres/src/lib.rs

					
				@ -0,0 +1,335 @@

				use std::time::Duration;

Added PostgresConfig struct with configurable max_connections and acquire_timeout. Defaults are now more sensible (10 connections, 30s timeout) and can be overridden via PostgresEventStore::with_config(). Commit: 6831640

Added `PostgresConfig` struct with configurable `max_connections` and `acquire_timeout`. Defaults are now more sensible (10 connections, 30s timeout) and can be overridden via `PostgresEventStore::with_config()`. Commit: 6831640

jwilger (Migrated from github.com) reviewed

2025-12-03 15:16:44 -08:00

eventcore-postgres/src/lib.rs

					
				@ -0,0 +1,335 @@

				use std::time::Duration;

Replaced with general-purpose from_pool() that's not test-specific. Users who want full control over pool configuration (or want to share a pool) can use this. Commit: 6831640

Replaced with general-purpose `from_pool()` that's not test-specific. Users who want full control over pool configuration (or want to share a pool) can use this. Commit: 6831640

jwilger (Migrated from github.com) reviewed

2025-12-03 15:17:06 -08:00

eventcore-postgres/src/lib.rs

					
				@ -0,0 +119,4 @@

				                }

				            })?;

				            events.push(event);

				        }

In event sourcing, streams typically represent bounded aggregates (single order, account, etc.) which should stay relatively small—usually under a few hundred events. Streams with thousands of events are a design smell suggesting the aggregate boundary is too large.

For typical aggregate sizes, fetch_all is perfectly fine. The real pain point would be ~10K+ events where memory becomes a concern. If we see that pattern emerge, we could add:

Pagination (read_stream_from_version)
Streaming via sqlx::query().fetch()
Snapshots (standard event sourcing optimization)

For now, keeping it simple. Happy to add streaming later if there's a concrete use case.

In event sourcing, streams typically represent bounded aggregates (single order, account, etc.) which should stay relatively small—usually under a few hundred events. Streams with thousands of events are a design smell suggesting the aggregate boundary is too large. For typical aggregate sizes, `fetch_all` is perfectly fine. The real pain point would be ~10K+ events where memory becomes a concern. If we see that pattern emerge, we could add: 1. Pagination (`read_stream_from_version`) 2. Streaming via `sqlx::query().fetch()` 3. Snapshots (standard event sourcing optimization) For now, keeping it simple. Happy to add streaming later if there's a concrete use case.

jwilger (Migrated from github.com) reviewed

2025-12-03 15:17:16 -08:00

src/store.rs

					
				@ -190,1 +219,3 @@

				    derive(Debug, Clone, PartialEq, Eq, Hash, AsRef, Deref, Display)

				    derive(

				        Debug,

				        Clone,

nutype generates a validated newtype where construction can fail (try_new returns Result). With #[derive(Serialize, Deserialize)], deserialization would bypass validation and accept any string, including empty or overly long ones.

The manual impl ensures deserialization goes through StreamId::try_new(), preserving the invariants (non-empty, max 255 chars, trimmed). This is the standard pattern for validated newtypes—serialize the inner value, deserialize with validation.

nutype generates a validated newtype where construction can fail (`try_new` returns `Result`). With `#[derive(Serialize, Deserialize)]`, deserialization would bypass validation and accept any string, including empty or overly long ones. The manual impl ensures deserialization goes through `StreamId::try_new()`, preserving the invariants (non-empty, max 255 chars, trimmed). This is the standard pattern for validated newtypes—serialize the inner value, deserialize with validation.

jwilger (Migrated from github.com) reviewed

2025-12-03 15:32:21 -08:00

eventcore-postgres/src/lib.rs

					
				@ -0,0 +193,4 @@

				        Ok(EventStreamSlice)

				    }

				}

Implemented trigger-based version management as discussed. The PostgreSQL trigger now:

Auto-assigns gap-free versions - stream_version is automatically set to MAX + 1
Validates expected versions - Checks session config eventcore.expected_versions and raises P0001 on mismatch
Cannot be bypassed - Database enforces the rules, not application code

App code is now much simpler - just sets expected versions via set_config() and INSERTs. No version calculation, no explicit transactions for locking.

Commit: 9ea33cd

Implemented trigger-based version management as discussed. The PostgreSQL trigger now: 1. **Auto-assigns gap-free versions** - `stream_version` is automatically set to `MAX + 1` 2. **Validates expected versions** - Checks session config `eventcore.expected_versions` and raises `P0001` on mismatch 3. **Cannot be bypassed** - Database enforces the rules, not application code App code is now much simpler - just sets expected versions via `set_config()` and INSERTs. No version calculation, no explicit transactions for locking. Commit: 9ea33cd

jwilger (Migrated from github.com) reviewed

2025-12-03 15:56:39 -08:00

src/store.rs

					
				@ -190,1 +219,3 @@

				    derive(Debug, Clone, PartialEq, Eq, Hash, AsRef, Deref, Display)

				    derive(

				        Debug,

				        Clone,

I thought that the nutype library had specific serde support through a feature flag. Can you double check on that and make the adjustment if it does?

jwilger (Migrated from github.com) reviewed

2025-12-03 16:06:00 -08:00

.config/nextest.toml

Addressed by removing the limitation entirely:

Deleted low-value migration tests (i005, i014) that needed to drop tables. These tests were redundant - if migrations fail, the contract tests fail anyway.
Using unique stream IDs with UUIDs for test isolation, allowing tests to run in parallel without conflicts.

All 78 tests now run in parallel in ~4 seconds.

Addressed by removing the limitation entirely: 1. **Deleted low-value migration tests** (i005, i014) that needed to drop tables. These tests were redundant - if migrations fail, the contract tests fail anyway. 2. **Using unique stream IDs with UUIDs** for test isolation, allowing tests to run in parallel without conflicts. All 78 tests now run in parallel in ~4 seconds.

jwilger (Migrated from github.com) reviewed

2025-12-03 16:09:22 -08:00

src/store.rs

					
				@ -190,1 +219,3 @@

				    derive(Debug, Clone, PartialEq, Eq, Hash, AsRef, Deref, Display)

				    derive(

				        Debug,

				        Clone,

You're right - nutype does have serde support through the serde feature flag (which was already enabled in Cargo.toml). Updated to use the derive instead of manual implementation.

You're right - nutype does have serde support through the `serde` feature flag (which was already enabled in Cargo.toml). Updated to use the derive instead of manual implementation.

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