ClickHouse の運用

CREATE TABLE analytics.dim_taxi_zones (
    zone_id      UInt16,
    borough      String,
    service_zone String
) ENGINE = MergeTree()
ORDER BY zone_id;

CREATE TABLE analytics.fact_trips (
    trip_id     String,
    pickup_at   DateTime,
    total_amount Float64,
    updated_at  DateTime
) ENGINE = ReplacingMergeTree(updated_at)
ORDER BY (pickup_at, trip_id);

-- Without FINAL: may return duplicates if merges haven't run
SELECT * FROM analytics.fact_trips WHERE trip_id = 'abc';

-- With FINAL: forces deduplication at query time (slower, always correct)
SELECT * FROM analytics.fact_trips FINAL WHERE trip_id = 'abc';

-- Trigger-based: only sees the rows inserted in the current batch
CREATE MATERIALIZED VIEW analytics.mv_realtime_counts
TO analytics.counts_table AS
SELECT pickup_date, count() AS trips
FROM default.trips_raw
GROUP BY pickup_date;

-- Refreshable: runs the full SELECT every 3 minutes
CREATE MATERIALIZED VIEW analytics.mv_hourly_revenue
REFRESH EVERY 180 SECOND AS
SELECT
    toStartOfHour(pickup_at) AS hour_bucket,
    pickup_borough,
    sum(total_amount)        AS revenue
FROM analytics.fact_trips FINAL
GROUP BY hour_bucket, pickup_borough;

ALTER TABLE analytics.mv_hourly_revenue MODIFY REFRESH EVERY 60 SECOND;

-- Good: low cardinality (borough, ~6 values) first, then high cardinality (trip_id)
ORDER BY (pickup_borough, toStartOfMonth(pickup_at), trip_id)

-- Bad: high cardinality first — the index can't skip anything useful
ORDER BY (trip_id, pickup_borough, pickup_at)

-- Snowflake
CLUSTER BY (DATE_TRUNC('month', PICKUP_AT), PICKUP_LOCATION_ID)

-- ClickHouse equivalent
ORDER BY (toStartOfMonth(pickup_at), pickup_location_id, trip_id)
-- Note: trip_id added as tiebreaker to ensure unique sort order

-- Add a bloom filter skip index on payment_type
ALTER TABLE analytics.fact_trips
ADD INDEX idx_payment_type payment_type TYPE bloom_filter GRANULARITY 4;

-- Float (returns 0.0 if key missing or wrong type)
JSONExtractFloat(trip_metadata, 'driver', 'rating')

-- String (returns '' if missing)
JSONExtractString(trip_metadata, 'app', 'version')

-- Integer (returns 0 if missing)
JSONExtractInt(trip_metadata, 'driver', 'id')

-- Bool (returns 0/1)
JSONExtractBool(trip_metadata, 'app', 'is_shared')

-- Raw value as string (preserves JSON sub-object)
JSONExtractRaw(trip_metadata, 'route')

yesterday()              -- today() - 1 day
toStartOfWeek(col)       -- Monday of the containing week
toStartOfQuarter(col)    -- first day of the quarter
toYear(col)              -- extract year as integer
toMonth(col)             -- extract month as integer (1-12)
toDayOfWeek(col)         -- 1=Monday, 7=Sunday

-- ClickHouse
now() - INTERVAL 7 DAY
now() - INTERVAL 1 HOUR
now() - INTERVAL 30 MINUTE
pickup_at + INTERVAL 90 SECOND

-- Snowflake equivalent
DATEADD('day', -7, CURRENT_TIMESTAMP())
DATEADD('hour', -1, CURRENT_TIMESTAMP())

-- Exact (like Snowflake COUNT(DISTINCT ...))
SELECT uniqExact(trip_id) FROM analytics.fact_trips FINAL;

-- Approximate — good for "how many unique passengers today?"
SELECT uniq(passenger_id) FROM analytics.fact_trips FINAL;

-- P95 trip duration — approximate but uses O(1) memory
SELECT quantileTDigest(0.95)(duration_minutes)
FROM analytics.fact_trips FINAL;

-- Multiple percentiles in one pass
SELECT quantileTDigestMerge(0.5)(state), quantileTDigestMerge(0.95)(state)
FROM analytics.fact_trips FINAL;

-- From 04_create_dictionary.sql
CREATE DICTIONARY analytics.taxi_zones_dict (
    zone_id      UInt16,
    borough      String,
    service_zone String
)
PRIMARY KEY zone_id
SOURCE(CLICKHOUSE(
    TABLE 'dim_taxi_zones'
    DB    'analytics'
))
LIFETIME(MIN 300 MAX 600)   -- refresh every 5-10 minutes
LAYOUT(FLAT());             -- hash map, best for < 1M rows

-- Instead of: JOIN analytics.dim_taxi_zones USING (zone_id)
SELECT
    trip_id,
    dictGet('analytics.taxi_zones_dict', 'borough', toUInt64(pickup_location_id)) AS pickup_borough,
    dictGet('analytics.taxi_zones_dict', 'borough', toUInt64(dropoff_location_id)) AS dropoff_borough
FROM analytics.fact_trips FINAL;

-- Read approximately 10% of rows
SELECT count(), avg(total_amount)
FROM analytics.fact_trips SAMPLE 0.1;

-- Read a specific number of rows (approximately)
SELECT trip_id, pickup_at, total_amount
FROM analytics.fact_trips SAMPLE 1000000;

-- Estimate total revenue from 10% sample
SELECT sum(total_amount) * 10 AS estimated_total_revenue
FROM analytics.fact_trips SAMPLE 0.1;

-- What dbt generates for incremental models
DELETE FROM analytics.fact_trips WHERE trip_id IN (SELECT trip_id FROM __dbt_tmp);
INSERT INTO analytics.fact_trips SELECT * FROM __dbt_tmp;

{{
    config(
        materialized='incremental',
        incremental_strategy='delete_insert',
        unique_key='trip_id',
        engine='ReplacingMergeTree(updated_at)',
        order_by='(pickup_at, trip_id)'
    )
}}

{{
    config(
        engine='MergeTree()',
        order_by='(zone_id)'
    )
}}

# ~/.dbt/profiles.yml
nyc_taxi_ch:
  target: dev
  outputs:
    dev:
      type: clickhouse
      host: "{{ env_var('CLICKHOUSE_HOST') }}"
      port: 8443
      user: default
      password: "{{ env_var('CLICKHOUSE_PASSWORD') }}"
      schema: analytics       # default database for models without a custom schema
      secure: true
      threads: 4

-- macros/generate_schema_name.sql
{% macro generate_schema_name(custom_schema_name, node) -%}
  {%- if custom_schema_name is none -%}
    {{ target.schema }}
  {%- else -%}
    {{ custom_schema_name }}
  {%- endif -%}
{%- endmacro %}