feat(outbox-store): Use executeBatch() after processing entries instead of single executeUpdate() for each entry

[rawo]

Implements KOJAK-75: replaces N individual updateAfterProcessing() calls per outbox batch with a single batched JDBC write, cutting per-batch DB roundtrips from N to 1.

• OutboxStore.updateAfterProcessingBatch(entries) — new method with a default implementation that loops updateAfterProcessing() one at a time, so existing implementations (test stubs, future stores) don't break.
• PostgresOutboxStore / MysqlOutboxStore override it with a single PreparedStatement reused across all entries via addBatch() / executeBatch(), touching only the 5 mutable columns (status, updated_at, retries, last_attempt, last_error) rather than the full 11-column upsert persist() uses. Postgres binds the id with setObject(uuid); MySQL binds it with setString(uuid.toString()) (CHAR(36) column, no native UUID type).
• OutboxProcessor.processNext() now calls store.updateAfterProcessingBatch(processed) once per drained batch instead of looping updateAfterProcessing() per entry.

Benchmark

New OutboxStoreUpdateBatchBenchmark (JMH) isolates the update phase for 1000 entries:

Method	ms/op (per entry)	Total for 1000 entries	Improvement
individualUpdates	0.188 ± 0.008	~187.6 ms	baseline
batchUpdate	0.018 ± 0.002	~18.3 ms	10.2×

Full writeup and raw JSON in benchmarks/results-postopt-KOJAK-75.md.

Test plan

• Unit tests: OutboxStoreTest (default updateAfterProcessingBatch loop behavior, incl. empty list), OutboxProcessorTest (asserts processNext() calls the batch method exactly once, never per-entry)
• Integration tests: OutboxStoreContractTests — mixed final statuses (DELIVERED + PENDING retry + FAILED) persisted via one updateAfterProcessingBatch() call, run against both Postgres and MySQL
• ./gradlew ktlintCheck clean
• ./gradlew build green (core, postgres, mysql, micrometer, integration-tests, spring-boot)

Refs: KOJAK-75 (blocked-by KOJAK-73, already merged — deliverBatch fire-flush-await)

[Copilot]

Pull request overview

This PR implements KOJAK-75 by adding a batch update API to OutboxStore and switching the processing pipeline to persist delivery results using a single JDBC executeBatch() call per drained outbox batch, reducing DB roundtrips from N to 1 for the “update-after-processing” phase.

Changes:

• Added OutboxStore.updateAfterProcessingBatch(entries) with a default per-entry fallback implementation.
• Implemented optimized JDBC batch updates in PostgresOutboxStore and MysqlOutboxStore, updating only the mutable delivery-state columns.
• Updated OutboxProcessor.processNext() to call the new batch update method once per processed batch; added unit + integration tests plus a JMH benchmark and benchmark artifacts.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
okapi-postgres/src/main/kotlin/com/softwaremill/okapi/postgres/PostgresOutboxStore.kt	Adds Postgres batch UPDATE via addBatch()/executeBatch() and extracts SQL strings to companion object.
okapi-mysql/src/main/kotlin/com/softwaremill/okapi/mysql/MysqlOutboxStore.kt	Adds MySQL batch UPDATE via addBatch()/executeBatch() and extracts SQL strings to companion object.
okapi-integration-tests/src/test/kotlin/com/softwaremill/okapi/test/store/OutboxStoreContractTests.kt	Adds contract test verifying mixed-status batch persistence works end-to-end.
okapi-core/src/test/kotlin/com/softwaremill/okapi/core/OutboxStoreTest.kt	Adds unit tests for default updateAfterProcessingBatch fallback behavior.
okapi-core/src/test/kotlin/com/softwaremill/okapi/core/OutboxProcessorTest.kt	Adds unit test asserting the processor calls the batch method exactly once and never per-entry.
okapi-core/src/main/kotlin/com/softwaremill/okapi/core/OutboxStore.kt	Introduces the new default batch update method on the store interface.
okapi-core/src/main/kotlin/com/softwaremill/okapi/core/OutboxProcessor.kt	Switches persistence step from per-entry updates to a single batch update call.
okapi-benchmarks/src/jmh/kotlin/com/softwaremill/okapi/benchmarks/OutboxStoreUpdateBatchBenchmark.kt	Adds JMH benchmark isolating the update phase and comparing individual vs batch updates.
benchmarks/results-postopt-KOJAK-75.md	Documents benchmark methodology and results for the batch update optimization.
benchmarks/outbox-store-update-batch.json	Stores raw JMH output for the reported benchmark run.

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[Copilot]

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated 2 comments.

[ramafasa]

LGTM