Trino federated query architecture

Trino Federated Query Architecture

When to Use

• Joining data from multiple systems (data lake + operational DB + Kafka) in a single query
• Deciding whether to use live federation or pre-materialization
• Designing a cross-domain reporting layer without moving data
• Understanding performance implications before writing a cross-catalog query

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Federation Architecture

┌──────────────────────────────────────────────────────────────────┐
│                     Trino Federated Query Layer                  │
│                                                                  │
│  SELECT f.amount, c.region, p.name                               │
│  FROM iceberg.gold.fact_orders f                                 │
│  JOIN postgresql.public.customers c ON f.customer_id = c.id     │
│  JOIN mysql.inventory.products p ON f.product_id = p.id         │
│                                                                  │
│  ┌──────────────┐  ┌──────────────┐  ┌──────────────┐           │
│  │  Iceberg     │  │ PostgreSQL   │  │   MySQL      │           │
│  │  (S3/Parquet)│  │ (JDBC)       │  │  (JDBC)      │           │
│  └──────────────┘  └──────────────┘  └──────────────┘           │
└──────────────────────────────────────────────────────────────────┘

---

Connector Performance Characteristics

Understanding how each connector fetches data is essential for correct federation design:

Connector	Fetch Method	Parallelism	Pushdown Support
Iceberg	Parallel split reads (Parquet/ORC)	High (1 split per file)	Predicate, projection, aggregation, limit
Hive	Parallel split reads	High	Predicate, projection
PostgreSQL	JDBC serial cursor	Low (1 connection per table)	Predicate, aggregation, join, limit, topn
MySQL	JDBC serial cursor	Low	Predicate, aggregation, limit
ClickHouse	JDBC	Low	Predicate, aggregation
Kafka	Per-partition readers	Medium	Limited (topic + timestamp range)
MongoDB	Cursor-based	Low	Predicate
JMX	In-memory	N/A	None

Key insight: Iceberg/Hive reads scale with worker count. JDBC connectors (PostgreSQL, MySQL) make a single serial connection — Trino fetches all rows then filters/joins in memory. For large JDBC tables, always push predicates down.

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Cross-Catalog JOIN Patterns

Pattern 1: Small Dimension from PostgreSQL (Broadcast)

-- GOOD: PostgreSQL table is small (< 100MB), broadcasts to all workers
-- Trino fetches entire table from PG into worker memory, then broadcasts
SELECT
    f.order_id,
    f.amount,
    c.region,
    c.tier
FROM iceberg.silver.orders f
JOIN postgresql.public.customers c
  ON f.customer_id = c.id
WHERE f.order_date = DATE '2024-06-01'   -- predicate pushed into Iceberg (partition prune)
  AND c.tier = 'premium';               -- predicate pushed into PostgreSQL query

-- EXPLAIN shows: BROADCAST exchange for the PG join

Pattern 2: Large JDBC Table → Pre-Materialize First

-- BAD: joining 50M-row PG table directly — Trino fetches 50M rows serially over JDBC
SELECT f.amount, p.product_name
FROM iceberg.silver.orders f
JOIN postgresql.catalog.products p ON f.product_id = p.id;   -- 50M rows from PG!

-- GOOD: materialize the large PG table into Iceberg daily
CREATE TABLE iceberg.silver.products_snapshot
WITH (format = 'PARQUET', compression_codec = 'ZSTD')
AS SELECT id, product_name, category, price, updated_at
   FROM postgresql.catalog.products;

-- Now join two Iceberg tables (parallel, pushdown, fast)
SELECT f.amount, p.product_name
FROM iceberg.silver.orders f
JOIN iceberg.silver.products_snapshot p ON f.product_id = p.id;

Pattern 3: Kafka Event Preview (Read-Once)

-- Query Kafka topic as a table (reads current offset window)
-- Note: results are non-repeatable — each query reads different offsets
SELECT
    _timestamp,
    json_extract_scalar(cast(_message as VARCHAR), '$.event_type') AS event_type,
    json_extract_scalar(cast(_message as VARCHAR), '$.user_id')    AS user_id
FROM kafka.default."prod.user.events.v1"
WHERE _timestamp > NOW() - INTERVAL '1' HOUR
LIMIT 1000;

Pattern 4: Cross-Schema Enrichment (Same Catalog)

-- Cross-schema within same Iceberg catalog — same connector, full pushdown
SELECT
    o.order_id,
    o.amount,
    c.name     AS customer_name,
    c.region,
    p.product_name
FROM iceberg.silver.orders o
JOIN iceberg.silver.customers c ON o.customer_id = c.customer_id
JOIN iceberg.gold.dim_product p ON o.product_id  = p.product_id
WHERE o.order_date = DATE '2024-06-01';

---

Predicate Pushdown Strategy

Always write predicates to enable connector-level filtering:

-- GOOD: predicate on PG side is pushed down (becomes WHERE in PG query)
SELECT * FROM postgresql.public.orders
WHERE status = 'shipped'        -- pushed to PG: SELECT * WHERE status='shipped'
  AND created_at > NOW() - INTERVAL '7' DAY;

-- VERIFY: EXPLAIN (TYPE IO) shows constraint on columns
EXPLAIN (TYPE IO)
SELECT * FROM postgresql.public.orders WHERE status = 'shipped';
-- → "constraint": {"columnConstraints": [{"columnName": "status", "domain": "shipped"}]}

PostgreSQL connector limitation: range predicates on VARCHAR columns are NOT pushed down (only equality):

-- This pushes down (equality on VARCHAR):
WHERE country = 'US'

-- This does NOT push down (range on VARCHAR):
WHERE country BETWEEN 'A' AND 'M'   -- full table scan in PG, filter in Trino

---

Materialization Decision Matrix

JDBC Table Size	Query Frequency	Strategy
< 10MB	Any	Live federation (broadcast)
10MB–500MB	< 1/hour	Live federation with predicate pushdown
> 500MB	> 1/day	Daily CTAS snapshot into Iceberg
> 500MB	< 1/week	Live federation with tight predicates
Any	Real-time	Keep in JDBC, use Debezium→Iceberg CDC

---

Snapshot Pattern: JDBC → Iceberg

-- Daily incremental snapshot (append new/changed rows)
CREATE TABLE IF NOT EXISTS iceberg.silver.pg_orders_snapshot (
    order_id    BIGINT,
    customer_id BIGINT,
    status      VARCHAR,
    amount      DECIMAL(18,2),
    updated_at  TIMESTAMP(6)
) WITH (
    format       = 'PARQUET',
    partitioning = ARRAY['day(updated_at)']
);

-- Incremental load (Airflow task, run daily)
INSERT INTO iceberg.silver.pg_orders_snapshot
SELECT order_id, customer_id, status, CAST(amount AS DECIMAL(18,2)), updated_at
FROM postgresql.public.orders
WHERE updated_at >= TIMESTAMP '{{ yesterday_ds }} 00:00:00'
  AND updated_at <  TIMESTAMP '{{ ds }} 00:00:00';

---

Multi-Source Reporting Query

-- Report combining Iceberg lake + PostgreSQL OLTP + ClickHouse analytics
-- All predicates pushed to respective connectors
SELECT
    o.order_date,
    c.region                           AS customer_region,
    p.category                         AS product_category,
    COUNT(o.order_id)                  AS order_count,
    SUM(o.amount)                      AS revenue,
    MAX(ch.page_views)                 AS peak_page_views
FROM iceberg.silver.orders o                               -- Iceberg: parallel scan
JOIN postgresql.public.customers c                         -- PG: small table, broadcast
  ON o.customer_id = c.id
JOIN iceberg.gold.dim_product p                            -- Iceberg: broadcast
  ON o.product_id = p.product_id
LEFT JOIN clickhouse.analytics.daily_traffic ch            -- ClickHouse: aggregated
  ON o.order_date = ch.event_date AND c.region = ch.region
WHERE o.order_date BETWEEN DATE '2024-01-01' AND DATE '2024-03-31'
  AND c.tier IN ('premium', 'enterprise')
GROUP BY o.order_date, c.region, p.category
ORDER BY revenue DESC
LIMIT 100;

---

Catalog Isolation Design

Separate catalogs by domain and access scope:

etc/catalog/
├── iceberg.properties          → lake data (Iceberg on S3)
├── iceberg_external.properties → external Iceberg (read-only partner data)
├── postgresql_orders.properties → orders OLTP DB (read-only replica)
├── postgresql_users.properties  → users OLTP DB (read-only replica)
├── clickhouse.properties        → analytics ClickHouse
├── kafka.properties             → event streaming (read-only)
└── tpch.properties              → TPC-H test data

Use resource groups to restrict which users can query which catalogs:

{
  "selectors": [
    {
      "user": ".*",
      "queryType": "SELECT",
      "queryText": ".*postgresql_orders.*",
      "group": "global.readonly.readonly_${USER}"
    }
  ]
}

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Anti-Patterns

1. Joining two large JDBC tables cross-connector — both tables are fetched serially and joined in Trino memory; a 10M×5M JDBC join moves 15M rows over JDBC before any join; always materialize at least one side into Iceberg.
2. No predicate on JDBC side in cross-catalog query — Trino fetches the entire JDBC table when predicates can't be pushed; always include at least one equality predicate on a JDBC table.
3. Querying Kafka topics in production reports — Kafka connector reads are non-repeatable and non-deterministic; use for exploration only; for production, sink Kafka to Iceberg via Flink/Debezium.
4. No metadata caching on JDBC catalogs — each query does schema/stats lookups; set metadata.cache-ttl=5m in JDBC catalog config to avoid thundering herd of metadata requests.
5. Cross-catalog JOINs in scheduled dbt models — dbt incremental on top of JDBC sources creates large full-table scans per run; snapshot JDBC sources into Iceberg first, then run dbt transformations on Iceberg only.

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References

• Trino connectors: trino.io/docs/current/connector.html
• PostgreSQL connector: trino.io/docs/current/connector/postgresql.html
• Iceberg connector: trino.io/docs/current/connector/iceberg.html
• Kafka connector: trino.io/docs/current/connector/kafka.html
• Related skills: [[trino-lakehouse-platform-architect]], [[trino-query-optimization]], [[trino-iceberg-best-practices]]