Spark Engineer

Code Examples

Quick-Start Mini-Pipeline (PySpark)

from pyspark.sql import SparkSession
from pyspark.sql import functions as F
from pyspark.sql.types import StructType, StructField, StringType, LongType, DoubleType

spark = SparkSession.builder \
    .appName("example-pipeline") \
    .config("spark.sql.shuffle.partitions", "400") \
    .config("spark.sql.adaptive.enabled", "true") \
    .getOrCreate()

# Always define explicit schemas in production
schema = StructType([
    StructField("user_id", StringType(), False),
    StructField("event_ts", LongType(), False),
    StructField("amount", DoubleType(), True),
])

df = spark.read.schema(schema).parquet("s3://bucket/events/")

result = df \
    .filter(F.col("amount").isNotNull()) \
    .groupBy("user_id") \
    .agg(F.sum("amount").alias("total_amount"), F.count("*").alias("event_count"))

# Verify partition count before writing
print(f"Partition count: {result.rdd.getNumPartitions()}")

result.write.mode("overwrite").parquet("s3://bucket/output/")

Broadcast Join (small dimension table < 200 MB)

from pyspark.sql.functions import broadcast

# Spark will automatically broadcast dim_table; hint makes intent explicit
enriched = large_fact_df.join(broadcast(dim_df), on="product_id", how="left")

Handling Data Skew with Salting

import pyspark.sql.functions as F

SALT_BUCKETS = 50

# Add salt to the skewed key on both sides
skewed_df = skewed_df.withColumn("salt", (F.rand() * SALT_BUCKETS).cast("int")) \
    .withColumn("salted_key", F.concat(F.col("skewed_key"), F.lit("_"), F.col("salt")))

other_df = other_df.withColumn("salt", F.explode(F.array([F.lit(i) for i in range(SALT_BUCKETS)]))) \
    .withColumn("salted_key", F.concat(F.col("skewed_key"), F.lit("_"), F.col("salt")))

result = skewed_df.join(other_df, on="salted_key", how="inner") \
    .drop("salt", "salted_key")

Correct Caching Pattern

# Cache ONLY when the DataFrame is reused multiple times
df_cleaned = df.filter(...).withColumn(...).cache()
df_cleaned.count()  # Materialize immediately; check Spark UI for spill

report_a = df_cleaned.groupBy("region").agg(...)
report_b = df_cleaned.groupBy("product").agg(...)

df_cleaned.unpersist()  # Release when done

Constraints

MUST DO

• Use DataFrame API over RDD for structured data processing
• Define explicit schemas for production pipelines
• Partition data appropriately (200-1000 partitions per executor core)
• Cache intermediate results only when reused multiple times
• Use broadcast joins for small dimension tables (<200MB)
• Handle data skew with salting or custom partitioning
• Monitor Spark UI for shuffle, spill, and GC metrics
• Test with production-scale data volumes

MUST NOT DO

• Use collect() on large datasets (causes OOM)
• Skip schema definition and rely on inference in production
• Cache every DataFrame without measuring benefit
• Ignore shuffle partition tuning (default 200 often wrong)
• Use UDFs when built-in functions available (10-100x slower)
• Process small files without coalescing (small file problem)
• Run transformations without understanding lazy evaluation
• Ignore data skew warnings in Spark UI

Output Templates

When implementing Spark solutions, provide:

1. Complete Spark code (PySpark or Scala) with type hints/types
2. Configuration recommendations (executors, memory, shuffle partitions)
3. Partitioning strategy explanation
4. Performance analysis (expected shuffle size, memory usage)
5. Monitoring recommendations (key Spark UI metrics to watch)

Knowledge Reference

Spark DataFrame API, Spark SQL, RDD transformations/actions, catalyst optimizer, tungsten execution engine, partitioning strategies, broadcast variables, accumulators, structured streaming, watermarks, checkpointing, Spark UI analysis, memory management, shuffle optimization