LSM Ağacı — Yazmayı Ekleyerek Hızlanan Veritabanları

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-- One partition per card per day; rows inside are sorted newest first.
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CREATE TABLE IF NOT EXISTS card_events (
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    card_id     text,
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    day         date,
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    occurred_at timestamp,
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    event_id    uuid,
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    amount      decimal,
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    merchant    text,
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    PRIMARY KEY ((card_id, day), occurred_at, event_id)
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) WITH CLUSTERING ORDER BY (occurred_at DESC, event_id ASC)
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  AND compaction = {'class': 'TimeWindowCompactionStrategy', 'compaction_window_unit': 'DAYS', 'compaction_window_size': 1}
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  AND bloom_filter_fp_chance = 0.01
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  AND default_time_to_live = 31536000;

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@Table("card_events")
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record CardEvent(
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        @PrimaryKeyColumn(name = "card_id", type = PrimaryKeyType.PARTITIONED, ordinal = 0) String cardId,
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        @PrimaryKeyColumn(name = "day", type = PrimaryKeyType.PARTITIONED, ordinal = 1) LocalDate day,
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        @PrimaryKeyColumn(name = "occurred_at", type = PrimaryKeyType.CLUSTERED, ordinal = 2, ordering = Ordering.DESCENDING) Instant occurredAt,
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        @PrimaryKeyColumn(name = "event_id", type = PrimaryKeyType.CLUSTERED, ordinal = 3) UUID eventId,
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        BigDecimal amount,
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        String merchant) {
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}

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interface CardEventRepository extends CassandraRepository<CardEvent, MapId> {
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    List<CardEvent> findByCardIdAndDay(String cardId, LocalDate day);
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}
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@Service
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class CardEventLog {
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    private static final ZoneId ISTANBUL = ZoneId.of("Europe/Istanbul");
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    private final CardEventRepository events;
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    CardEventLog(CardEventRepository events) {
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        this.events = events;
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    }
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    // Append only: a correction is a new event, never an update or a delete (deletes are tombstones).
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    void record(String cardId, Instant at, BigDecimal amount, String merchant) {
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        events.insert(new CardEvent(cardId, LocalDate.ofInstant(at, ISTANBUL), at, UUID.randomUUID(), amount, merchant));
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    }
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    List<CardEvent> today(String cardId, Clock clock) {
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        return events.findByCardIdAndDay(cardId, LocalDate.now(clock.withZone(ISTANBUL)));
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    }
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}

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@DataCassandraTest
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@Testcontainers
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class CardEventLogIT {
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    @Container
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    @ServiceConnection
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    static CassandraContainer cassandra = new CassandraContainer("cassandra:5.0");
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    @Autowired CardEventRepository repository;
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    @Test
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    void eventsOfACardComeBackNewestFirst() {
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        CardEventLog log = new CardEventLog(repository);
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        Instant morning = Instant.parse("2026-10-03T07:00:00Z");
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        log.record("C1", morning, new BigDecimal("245.90"), "Migros");
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        log.record("C1", morning.plusSeconds(3600), new BigDecimal("60.00"), "Kahveci");
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        Clock clock = Clock.fixed(morning.plusSeconds(7200), ZoneOffset.UTC);
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        assertThat(log.today("C1", clock)).extracting(CardEvent::merchant).containsExactly("Kahveci", "Migros");
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    }
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}