Data Eng Warehouse Patterns

Data Warehouse Patterns

Core Principles

1. ELT over ETL — Load raw data into the warehouse first, then transform using SQL. Modern warehouses have the compute power to handle transformations at scale, eliminating fragile middleware.
2. Layered architecture — Organize data into staging (raw), transformation (cleaned/conformed), and presentation (business-ready) layers. Each layer has clear ownership and SLAs.
3. Immutable raw data — Never modify source data after landing. Treat the raw layer as an append-only audit log. All transformations produce new tables or views downstream.
4. Schema-on-read flexibility — Semi-structured data (JSON, Avro, Parquet) can be loaded without predefined schemas, then parsed and typed during transformation.
5. Cost-aware design — Warehouse compute is elastic but not free. Partition, cluster, and materialize strategically to minimize scan volume and compute spend.

ELT vs ETL Architecture

Modern cloud warehouses favor ELT because transformations run inside the warehouse engine, leveraging massive parallel processing. External ETL tools add latency, maintenance burden, and failure points.

-- ELT pattern: land raw JSON, then transform in-warehouse
-- Step 1: Load raw data into staging
COPY INTO raw.stripe_events
FROM @s3_stage/stripe/
FILE_FORMAT = (TYPE = JSON);

-- Step 2: Transform with SQL into clean layer
CREATE OR REPLACE TABLE cleaned.payments AS
SELECT
    raw:id::STRING                          AS event_id,
    raw:data:object:amount::NUMBER / 100    AS amount_dollars,
    raw:data:object:currency::STRING        AS currency,
    raw:created::TIMESTAMP_NTZ              AS event_timestamp,
    CURRENT_TIMESTAMP()                     AS _loaded_at
FROM raw.stripe_events
WHERE raw:type::STRING = 'charge.succeeded';

See elt-pipeline-patterns for: medallion architecture, incremental loading strategies, staging layer design.

Snowflake Patterns

Snowflake separates storage and compute with virtual warehouses. Use multi-cluster warehouses for concurrency, and leverage time travel and zero-copy clones for development.

-- Create a warehouse sized for heavy transformation workloads
CREATE WAREHOUSE transform_wh
    WAREHOUSE_SIZE = 'X-LARGE'
    AUTO_SUSPEND = 300
    AUTO_RESUME = TRUE
    MIN_CLUSTER_COUNT = 1
    MAX_CLUSTER_COUNT = 4
    SCALING_POLICY = 'STANDARD';

-- Cluster a large fact table on commonly filtered columns
ALTER TABLE analytics.fct_orders
    CLUSTER BY (order_date, region_id);

-- Use time travel to recover from bad writes
SELECT * FROM analytics.fct_orders
    AT(OFFSET => -3600);  -- state from 1 hour ago

See snowflake-patterns for: warehouse sizing guidelines, external stages, COPY INTO options, clustering key selection, time travel and cloning.

BigQuery Patterns

BigQuery is serverless — there are no clusters to manage. Optimize cost by partitioning tables, clustering on high-cardinality filter columns, and using materialized views to accelerate repeated queries.

-- Partitioned and clustered table for event analytics
CREATE TABLE analytics.user_events (
    event_id        STRING NOT NULL,
    user_id         STRING NOT NULL,
    event_name      STRING,
    event_params    ARRAY<STRUCT<key STRING, value STRING>>,
    device          STRUCT<category STRING, os STRING, browser STRING>,
    event_timestamp TIMESTAMP NOT NULL,
    _partition_date DATE NOT NULL
)
PARTITION BY _partition_date
CLUSTER BY user_id, event_name
OPTIONS (
    partition_expiration_days = 365,
    require_partition_filter  = TRUE
);

See bigquery-patterns for: partition strategies, nested/repeated fields, materialized views, BI Engine reservations, slot management.

Redshift Patterns

Redshift uses a shared-nothing MPP architecture. Distribution keys control how data is spread across nodes, and sort keys define on-disk ordering for range-restricted scans.

-- Fact table with optimized distribution and sort keys
CREATE TABLE analytics.fct_page_views (
    page_view_id    BIGINT IDENTITY(1,1),
    session_id      VARCHAR(64)     NOT NULL,
    user_id         BIGINT          DISTKEY,
    page_url        VARCHAR(2048),
    referrer_url    VARCHAR(2048),
    view_duration   INTEGER,
    view_timestamp  TIMESTAMP       SORTKEY,
    device_type     VARCHAR(32),
    country_code    VARCHAR(2)
)
DISTSTYLE KEY
COMPOUND SORTKEY (view_timestamp, user_id);

See redshift-patterns for: distribution styles (KEY, ALL, EVEN, AUTO), sort key types, COPY from S3, WLM configuration, Redshift Spectrum.

Lakehouse Architecture

Lakehouse combines the low-cost storage of data lakes with the ACID transactions and performance of data warehouses. Open table formats like Apache Iceberg and Delta Lake enable this convergence.

-- Apache Iceberg table creation in Snowflake (external volume)
CREATE ICEBERG TABLE bronze.web_clickstream (
    click_id        STRING,
    session_id      STRING,
    url             STRING,
    referrer        STRING,
    user_agent      STRING,
    click_timestamp TIMESTAMP,
    _loaded_at      TIMESTAMP
)
CATALOG = 'SNOWFLAKE'
EXTERNAL_VOLUME = 'iceberg_s3_vol'
BASE_LOCATION = 'clickstream/'
FILE_FORMAT = (TYPE = PARQUET);

-- Time travel with Iceberg snapshots
SELECT * FROM bronze.web_clickstream
    AT(TIMESTAMP => '2026-02-13 10:00:00'::TIMESTAMP);

See lakehouse-patterns for: Iceberg vs Delta Lake comparison, table format internals, schema evolution, partition evolution, time travel mechanics.

Data Vault 2.0 Overview

Data Vault 2.0 is a modeling methodology for enterprise data warehouses. It separates structural data (hubs, links) from descriptive data (satellites), enabling parallel loading and full historical tracking.

-- Hub: business key registry for customers
CREATE TABLE raw_vault.hub_customer (
    hub_customer_hk     BINARY(32)      NOT NULL,  -- SHA-256 hash key
    customer_bk         VARCHAR(64)     NOT NULL,  -- business key
    load_timestamp      TIMESTAMP_NTZ   NOT NULL,
    record_source       VARCHAR(128)    NOT NULL,
    CONSTRAINT pk_hub_customer PRIMARY KEY (hub_customer_hk)
);

-- Satellite: descriptive attributes with full history
CREATE TABLE raw_vault.sat_customer_details (
    hub_customer_hk     BINARY(32)      NOT NULL,
    load_timestamp      TIMESTAMP_NTZ   NOT NULL,
    load_end_timestamp  TIMESTAMP_NTZ,
    hash_diff           BINARY(32)      NOT NULL,  -- change detection
    first_name          VARCHAR(128),
    last_name           VARCHAR(128),
    email               VARCHAR(256),
    phone               VARCHAR(32),
    record_source       VARCHAR(128)    NOT NULL,
    CONSTRAINT pk_sat_cust PRIMARY KEY (hub_customer_hk, load_timestamp)
);

See data-vault-patterns for: hub/link/satellite design rules, hash key generation, point-in-time tables, bridge tables, business vault.

Anti-Patterns

Performance

• Partition pruning eliminates scanning irrelevant data segments. Always partition fact tables by date and enforce partition filters in BigQuery.
• Clustering physically co-locates related rows. Choose 2-4 high-cardinality columns that appear in WHERE and JOIN clauses.
• Materialized views pre-compute expensive aggregations. Use them for dashboards that hit the same GROUP BY patterns repeatedly.
• Result caching is automatic in most warehouses. Avoid unnecessary CURRENT_TIMESTAMP() or non-deterministic functions in cached queries.
• Warehouse sizing should match workload: upsize for large batch transforms, downsize for light interactive queries. Auto-suspend aggressively (60-300 seconds).
• Compression is automatic in columnar warehouses but file format matters at ingestion — prefer Parquet or ORC over CSV for bulk loads.
• Concurrency scaling (Snowflake) and flex slots (BigQuery) handle burst workloads without over-provisioning base capacity.
• Query profiling is essential. Use EXPLAIN, query history views, and warehouse utilization dashboards to find bottlenecks before optimizing blindly.

source: Cloud data warehouse documentation (Snowflake, BigQuery, Redshift), Data Vault 2.0 methodology, Apache Iceberg and Delta Lake specifications, dbt best practices

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