Snowflake Snowpark Python & dbt

This skill covers building production data transformation pipelines with Snowpark Python (Snowflake's server-side Python API) and with dbt using the dbt-snowflake adapter.

Workflow for a Snowpark or dbt Transformation

1. Snowpark: open a session — Build a Session from environment-scoped credentials, specifying role, warehouse, database, and schema explicitly.
2. Snowpark: express transforms with the DataFrame API — Prefer .filter(), .select(), .group_by().agg(), and .join() over raw SQL strings for reusable pipeline code; DataFrames are lazily evaluated and only execute on .collect()/.show()/a write action.
3. Snowpark: push compute server-side — Use scalar UDFs for row-wise logic, vectorized (pandas) UDFs for ML inference, UDTFs when one input row produces multiple output rows, and stored procedures for multi-step server-side orchestration.
4. dbt: model in layers — Staging models (stg_*) rename and type-cast; mart models express business logic on top of staging.
5. dbt: choose a materialization — view for cheap logic, table only when reads are frequent, incremental for large fact tables, dynamic_table for near-real-time freshness needs.
6. dbt: define sources and tests — Declare sources in _sources.yml with freshness thresholds; add unique/not_null tests on key columns.
7. dbt: run selectively — Use dbt run --select model+ (model and downstream) or +model (model and upstream) instead of full-project runs during iteration.
8. dbt: build and validate — Run dbt build (run + test in dependency order) before merging, and dbt docs generate to keep documentation current.

Snowpark Python

Snowpark runs Python server-side inside a Snowflake warehouse — data never leaves Snowflake. Core abstractions: Session, DataFrame, UDF, UDTF, UDAF, and Stored Procedure.

Session

import os
from snowflake.snowpark import Session

session = Session.builder.configs({
    "account": os.environ["SNOWFLAKE_ACCOUNT"],
    "user": os.environ["SNOWFLAKE_USER"],
    "password": os.environ["SNOWFLAKE_PASSWORD"],
    "role": "my_role", "warehouse": "my_wh", "database": "my_db", "schema": "my_schema",
}).create()

Never hardcode credentials — always read them from environment variables or a secrets manager.

DataFrame API

DataFrames are lazily evaluated: Snowpark builds a query plan and only executes it on collect()/show() or a write action.

df = session.table("customers")
df_filtered = df.filter(df["region"] == "US").select("name", "email", "revenue")
df_agg = df.group_by("region").agg(sum("revenue").alias("total_revenue"))
df_agg.show()

Key operations: .filter(), .select(), .group_by().agg(), .join(), .sort(), .with_column(), .drop(), .distinct(), .limit(), .union_all(), .flatten(), .write.save_as_table().

Scalar UDFs

from snowflake.snowpark.functions import udf

@udf(name="normalize_email", replace=True)
def normalize_email(email: str) -> str:
    return email.strip().lower() if email else None

Vectorized UDFs

Vectorized (pandas) UDFs are 10-100x faster than scalar UDFs for ML inference because they batch rows instead of invoking Python per row.

import pandas as pd
from snowflake.snowpark.functions import udf

@udf(name="predict_score", packages=["scikit-learn", "pandas"], replace=True)
def predict_score(features: pd.Series) -> pd.Series:
    import pickle, sys
    model = pickle.load(open(sys.path[0] + "/model.pkl", "rb"))
    return pd.Series(model.predict(features.values.reshape(-1, 1)))

UDTFs (return multiple rows per input)

from snowflake.snowpark.types import StructType, StructField, StringType

class Tokenizer:
    def process(self, text: str):
        for token in text.split():
            yield (token,)

tokenize = session.udtf.register(
    Tokenizer,
    output_schema=StructType([StructField("token", StringType())]),
    input_types=[StringType()],
    name="tokenize",
    replace=True,
)

Stored procedures

from snowflake.snowpark import Session
from snowflake.snowpark.functions import sproc

@sproc(name="daily_etl", replace=True, packages=["snowflake-snowpark-python"])
def daily_etl(session: Session) -> str:
    raw = session.table("raw_events")
    cleaned = raw.filter(raw["event_type"].is_not_null())
    cleaned.write.mode("overwrite").save_as_table("cleaned_events")
    return f"Processed {cleaned.count()} rows"

Packages and file access

• Add third-party packages with session.add_packages("pandas", "scikit-learn==1.3.0", "xgboost") — pin versions for production UDFs and stored procedures.
• Attach static files (e.g., a pickled model) with session.add_import("@my_stage/model.pkl").
• For pandas-on-Snowflake with no data movement to the client, use modin.pandas with the Snowpark plugin: import modin.pandas as pd; import snowflake.snowpark.modin.plugin; df = pd.read_snowflake("my_table").

dbt with the Snowflake Adapter

Install with pip install dbt-snowflake.

profiles.yml

my_project:
  target: dev
  outputs:
    dev:
      type: snowflake
      account: myaccount
      user: myuser
      password: "{{ env_var('SNOWFLAKE_PASSWORD') }}"
      role: transformer
      database: analytics
      warehouse: transforming
      schema: public
      threads: 4

Never commit real credentials into profiles.yml — always source secrets from env_var().

Materializations

Available materializations: view, table, incremental, ephemeral, dynamic_table. Default to view for cheap logic; reserve table for models read frequently enough to justify storage cost; use incremental for large fact tables and dynamic_table when near-real-time freshness matters.

Dynamic Tables in dbt

{{ config(materialized='dynamic_table', snowflake_warehouse='transforming', target_lag='1 hour') }}
SELECT customer_id, SUM(amount) AS lifetime_value FROM {{ ref('stg_orders') }} GROUP BY 1

Incremental models

{{
  config(
    materialized='incremental',
    unique_key='event_id',
    incremental_strategy='merge',
    on_schema_change='sync_all_columns'
  )
}}
SELECT * FROM {{ ref('stg_events') }}
{% if is_incremental() %}
  WHERE event_timestamp > (SELECT MAX(event_timestamp) FROM {{ this }})
{% endif %}

Always guard {{ this }} with {% if is_incremental() %} — referencing it unconditionally breaks the first (full) run, when the target table doesn't exist yet.

Snowflake-specific configs

• cluster_by=['col1', 'col2'] — clustering, large tables only (generally >1TB).
• transient=true — no Fail-safe, lower storage cost; use for staging models.
• query_tag='finance_daily' — workload attribution for cost tracking.
• copy_grants=true — preserve access grants across a CREATE OR REPLACE.
• snowflake_warehouse='lg_wh' — per-model warehouse override for heavy transforms.
• secure=true — secure views, for models exposing sensitive columns.

Sources with freshness checks

sources:
  - name: raw
    database: raw_db
    schema: jaffle_shop
    tables:
      - name: customers
        loaded_at_field: _loaded_at
        freshness:
          warn_after: {count: 12, period: hour}
          error_after: {count: 24, period: hour}

Testing

models:
  - name: stg_customers
    columns:
      - name: customer_id
        tests: [unique, not_null]

Key commands

• dbt run, dbt test, dbt build (run + test in dependency order), dbt compile
• dbt run --select my_model+ — model and everything downstream
• dbt run --select +my_model — model and everything upstream
• dbt source freshness — check source staleness against configured thresholds
• dbt docs generate && dbt docs serve — build and preview documentation

Custom schema naming

{% macro generate_schema_name(custom_schema_name, node) %}
  {% if custom_schema_name %}{{ custom_schema_name | trim }}{% else %}{{ target.schema }}{% endif %}
{% endmacro %}

Best Practices

• Prefer vectorized (pandas) UDFs over scalar UDFs for ML inference.
• Pin package versions in production UDFs and stored procedures.
• Use the Snowpark DataFrame API over raw SQL strings in reusable Python pipelines.
• Use staging models (stg_*) to rename and type-cast; keep business logic in mart models.
• Use incremental materialization for fact tables and dynamic_table for near-real-time needs.
• Set on_schema_change='sync_all_columns' on incremental models to handle upstream schema drift safely.
• Use copy_grants=true to avoid permission churn on rebuild, and tag models for selective execution.
• Use separate warehouses for dbt runs versus interactive analyst queries.

Anti-Patterns

• Do not .collect() large Snowpark DataFrames to the client — keep processing server-side.
• Do not use Python loops over rows in Snowpark — use DataFrame operations or vectorized UDFs.
• Do not reference {{ this }} in an incremental model without an {% if is_incremental() %} guard.
• Do not set cluster_by on small tables (under roughly 1TB) — the overhead outweighs the benefit.
• Do not default every model to materialized='table' — views are free until queried.
• Do not hardcode database/schema names in dbt models — use {{ ref() }} and {{ source() }}.