Cluster Configuration

Advanced⏱35-45 minutes📖2 min readLesson 6 of 10

Cluster Configuration

Configure Spark clusters: spark.sql.shuffle.partitions, spark.executor.memory, dynamic allocation, and resource optimization

Proper Spark configuration is essential for performance, stability, and cost efficiency. This lesson covers the most critical configuration parameters and how to tune them.

Configuration Priority

Spark configuration follows a hierarchy:

Priority	Source	Overrides
1 (Highest)	`spark-submit --conf`	All below
2	`SparkSession.conf.set()`	Config file defaults
3	`spark-defaults.conf`	Hardcoded defaults
4 (Lowest)	Hardcoded defaults	:

Core Resource Configuration

Executor Resources

python

from pyspark.sql import SparkSession

spark = SparkSession.builder \
    .appName("OptimizedApp") \
    .config("spark.executor.memory", "8g") \
    .config("spark.executor.cores", "4") \
    .config("spark.executor.instances", "10") \
    .config("spark.driver.memory", "4g") \
    .getOrCreate()

Resource Calculation Formula

Total cores = executor.instances × executor.cores
Total memory = executor.instances × executor.memory

Example:
  10 executors × 4 cores = 40 cores
  10 executors × 8g = 80g total memory
  Overhead: 8g × 0.1 = 0.8g per executor (spark.executor.memoryOverhead)

ℹ️Note

Leave 1-2 cores per node for OS and Hadoop services. For YARN, container overhead reduces available memory. Set spark.executor.memoryOverhead to 10-15% of executor memory for JVM overhead.

Memory Breakdown

python

# Default memory allocation within an executor
# spark.executor.memory = 8g
# spark.memory.fraction = 0.6 (60% for execution + storage)
# spark.memory.storageFraction = 0.5 (50% of unified for storage)
#
# Execution: 8g × 0.6 × 0.5 = 2.4g
# Storage:   8g × 0.6 × 0.5 = 2.4g  (can borrow from execution)
# Reserved:  8g × 0.4 = 3.2g (user code, overhead)

Shuffle Configuration

python

# Shuffle partitions
spark.conf.set("spark.sql.shuffle.partitions", "200")

# Rule of thumb: 2-4 partitions per core
# 40 cores × 3 = 120 partitions

# Shuffle memory buffer
spark.conf.set("spark.shuffle.file.buffer", "64k")
spark.conf.set("spark.reducer.maxSizeInFlight", "96m")

# Shuffle compression
spark.conf.set("spark.shuffle.compress", "true")
spark.conf.set("spark.shuffle.spill.compress", "true")
spark.conf.set("spark.io.compression.codec", "snappy")

Shuffle Parameter	Default	Description
`spark.sql.shuffle.partitions`	200	Partitions after shuffle
`spark.shuffle.file.buffer`	32k	Buffer size for shuffle writes
`spark.reducer.maxSizeInFlight`	48m	Max size of map output per reducer
`spark.shuffle.compress`	true	Compress shuffle output
`spark.shuffle.spill.compress`	true	Compress spilled data

Dynamic Allocation

Dynamic allocation adjusts executor count based on workload.

python

# Enable dynamic allocation
spark.conf.set("spark.dynamicAllocation.enabled", "true")
spark.conf.set("spark.dynamicAllocation.minExecutors", "2")
spark.conf.set("spark.dynamicAllocation.maxExecutors", "50")
spark.conf.set("spark.dynamicAllocation.initialExecutors", "5")
spark.conf.set("spark.dynamicAllocation.executorIdleTimeout", "60s")
spark.conf.set("spark.dynamicAllocation.cachedExecutorIdleTimeout", "120s")

# With shuffle tracking (keeps executors during shuffles)
spark.conf.set("spark.dynamicAllocation.shuffleTracking.enabled", "true")

✅Success

Dynamic allocation is essential for multi-tenant clusters. It automatically scales down when demand is low and scales up during peak loads, improving cluster utilization.

When to Use Dynamic Allocation

Scenario	Recommended
Multi-tenant YARN cluster	Yes
Dedicated cluster	Maybe (fixed allocation simpler)
Streaming workloads	Maybe (consider fixed for predictable latency)
Kubernetes	Yes (auto-scaling)
Short ad-hoc queries	Yes

Adaptive Query Execution (AQE)

python

# Enable AQE (default in Spark 3.x)
spark.conf.set("spark.sql.adaptive.enabled", "true")

# Dynamic partition coalescing
spark.conf.set("spark.sql.adaptive.coalescePartitions.enabled", "true")
spark.conf.set("spark.sql.adaptive.coalescePartitions.minPartitions", "10")
spark.conf.set("spark.sql.adaptive.coalescePartitions.maxPartitions", "500")
spark.conf.set("spark.sql.adaptive.coalescePartitions.parallelismFirst", "true")

# Skew join optimization
spark.conf.set("spark.sql.adaptive.skewJoin.enabled", "true")
spark.conf.set("spark.sql.adaptive.skewJoin.skewedPartitionFactor", "5")
spark.conf.set("spark.sql.adaptive.skewJoin.skewedPartitionThresholdInBytes", "256MB")

# Dynamic join switch (broadcast vs sort-merge)
spark.conf.set("spark.sql.adaptive.localShuffleReader.enabled", "true")

Serialization and Compression

python

# Kryo serialization (faster than Java serialization)
spark.conf.set("spark.serializer", "org.apache.spark.serializer.KryoSerializer")
spark.conf.set("spark.kryoserializer.buffer.max", "256m")
spark.conf.set("spark.kryo.registrationRequired", "false")

# Register custom classes for Kryo
spark.conf.set("spark.kryo.classesToRegister", 
    "com.example.MyClass,com.example.AnotherClass")

# RDD compression
spark.conf.set("spark.rdd.compress", "true")

# Broadcast compression
spark.conf.set("spark.broadcast.compress", "true")

Network and I/O

python

# Network timeouts
spark.conf.set("spark.network.timeout", "600s")
spark.conf.set("spark.executor.heartbeatInterval", "30s")
spark.conf.set("spark.sql.broadcastTimeout", "600")

# Max result size
spark.conf.set("spark.driver.maxResultSize", "4g")

# I/O optimizations
spark.conf.set("spark.hadoop.parquet.enable.summary-metadata", "false")
spark.conf.set("spark.sql.parquet.mergeSchema", "false")
spark.conf.set("spark.sql.parquet.filterPushdown", "true")

Task and Parallelism

python

# Task configuration
spark.conf.set("spark.task.maxFailures", "8")
spark.conf.set("spark.speculation", "true")
spark.conf.set("spark.speculation.interval", "100ms")
spark.conf.set("spark.speculation.multiplier", "1.5")

# Default parallelism
# spark.default.parallelism = max(2, total_cores)
# spark.sql.shuffle.partitions = 200

Common Configurations by Use Case

Batch ETL

python

spark.conf.set("spark.executor.memory", "4g")
spark.conf.set("spark.executor.cores", "4")
spark.conf.set("spark.sql.shuffle.partitions", "200")
spark.conf.set("spark.sql.adaptive.enabled", "true")
spark.conf.set("spark.dynamicAllocation.enabled", "true")

Machine Learning

python

spark.conf.set("spark.executor.memory", "16g")  # More memory for ML
spark.conf.set("spark.executor.cores", "4")
spark.conf.set("spark.sql.shuffle.partitions", "100")
spark.conf.set("spark.serializer", "org.apache.spark.serializer.KryoSerializer")
spark.conf.set("spark.kryoserializer.buffer.max", "256m")

Streaming

python

spark.conf.set("spark.executor.memory", "8g")
spark.conf.set("spark.executor.cores", "3")
spark.conf.set("spark.sql.shuffle.partitions", "10")  # Fewer partitions
spark.conf.set("spark.streaming.backpressure.enabled", "true")
spark.conf.set("spark.streaming.kafka.maxRatePerPartition", "1000")

Interactive/Ad-hoc

python

spark.conf.set("spark.executor.memory", "8g")
spark.conf.set("spark.sql.shuffle.partitions", "50")
spark.conf.set("spark.sql.adaptive.enabled", "true")
spark.conf.set("spark.dynamicAllocation.enabled", "true")
spark.conf.set("spark.dynamicAllocation.maxExecutors", "20")

Configuration CLI Examples

bash

# spark-submit with configuration
spark-submit \
  --class com.example.Main \
  --master yarn \
  --deploy-mode cluster \
  --num-executors 20 \
  --executor-memory 8g \
  --executor-cores 4 \
  --driver-memory 4g \
  --conf spark.sql.shuffle.partitions=200 \
  --conf spark.sql.adaptive.enabled=true \
  --conf spark.dynamicAllocation.enabled=true \
  --conf spark.serializer=org.apache.spark.serializer.KryoSerializer \
  app.jar

Practice Questions

What is the formula for calculating total cluster resources?
How does spark.memory.fraction divide executor memory?
When should you enable dynamic allocation?
What is the recommended value for spark.sql.shuffle.partitions?
How does AQE improve shuffle partition distribution?
What is the advantage of Kryo serialization over Java serialization?
How does speculation help with straggler tasks?
What configuration changes would you make for a streaming workload vs batch?
Why is spark.sql.shuffle.partitions set lower for streaming?
How do you configure Spark for a memory-intensive ML workload?

Progress60%

GraphX

Memory Tuning

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Course Content

1. Structured Streaming 2. Window Operations and Watermarking 3. Introduction to MLlib 4. ML Pipelines and Hyperparameter Tuning 5. GraphX 6. Cluster Configuration 7. Memory Tuning 8. Delta Lake 9. Monitoring and Debugging 10. Advanced Project: Real-Time Streaming Analytics with ML Inference