Incremental processing patterns in Apache Spark

Introduction

Incremental processing helps handle new data without redoing everything. It saves time and resources by updating only what changed.

When new data arrives regularly, like daily sales records.

When processing large datasets where full reprocessing is slow.

When you want to update reports or dashboards with fresh data quickly.

When working with streaming data that comes in small batches.

When you want to keep data lakes or warehouses up to date efficiently.

Syntax

Apache Spark

spark.read.format("delta").load("path/to/table")
  .filter("date > last_processed_date")
  .write.format("delta")
  .mode("append")
  .save("path/to/table")

This example uses Delta Lake format for incremental updates.

Filtering new data by a date or timestamp column is common.

Examples

This example finds new rows by excluding existing IDs and appends them.

Apache Spark

new_data = spark.read.format("csv").load("new_data.csv")

existing_data = spark.read.format("delta").load("/data/delta_table")

incremental_data = new_data.join(existing_data, "id", "left_anti")

incremental_data.write.format("delta").mode("append").save("/data/delta_table")

This example shows how to merge updates and inserts using Delta Lake's merge.

Apache Spark

from delta.tables import DeltaTable

deltaTable = DeltaTable.forPath(spark, "/data/delta_table")

updatesDF = spark.read.format("csv").load("updates.csv")

deltaTable.alias("t").merge(
    updatesDF.alias("u"), "t.id = u.id")
  .whenMatchedUpdate(set = {"value": "u.value"})
  .whenNotMatchedInsertAll()
  .execute()

Sample Program

This program creates a Delta table with initial data, then merges new data that updates and adds records. Finally, it shows the updated table.

Apache Spark

from pyspark.sql import SparkSession
from delta.tables import DeltaTable

spark = SparkSession.builder.appName("IncrementalProcessingExample")
    .config("spark.sql.extensions", "io.delta.sql.DeltaSparkSessionExtension")
    .config("spark.sql.catalog.spark_catalog", "org.apache.spark.sql.delta.catalog.DeltaCatalog")
    .getOrCreate()

# Simulate existing data
existing_data = spark.createDataFrame([
    (1, "Alice", 100),
    (2, "Bob", 200)
], ["id", "name", "amount"])

existing_data.write.format("delta").mode("overwrite").save("/tmp/delta_table")

deltaTable = DeltaTable.forPath(spark, "/tmp/delta_table")

# New incoming data with one new and one updated record
new_data = spark.createDataFrame([
    (2, "Bob", 250),  # updated amount
    (3, "Charlie", 300)  # new record
], ["id", "name", "amount"])

# Merge new data into existing delta table
(deltaTable.alias("t")
 .merge(new_data.alias("n"), "t.id = n.id")
 .whenMatchedUpdate(set={"name": "n.name", "amount": "n.amount"})
 .whenNotMatchedInsertAll()
 .execute())

# Show final table
final_df = spark.read.format("delta").load("/tmp/delta_table")
final_df.orderBy("id").show()

Important Notes

Incremental processing reduces work by handling only new or changed data.

Delta Lake supports easy merges for incremental updates.

Always have a unique key to identify records for merging.

Summary

Incremental processing updates data efficiently by working only on new or changed parts.

Use filtering or merging to handle incremental data in Spark.

Delta Lake is a helpful tool for incremental data management.

Practice

1.

What is the main idea behind incremental processing in Apache Spark?

easy

A. Delete old data before processing new data

B. Process all data repeatedly for accuracy

C. Process only new or changed data instead of all data every time

D. Use only batch processing without updates

Solution

1. Step 1: Understand incremental processing concept

   Incremental processing means working only on data that is new or has changed, not the entire dataset.

2. Step 2: Compare options to concept

   Process only new or changed data instead of all data every time matches this idea, while others describe full or batch processing.

3. Final Answer:

   Process only new or changed data instead of all data every time -> Option C

4. Quick Check:

   Incremental processing = new or changed data only [OK]

Hint: Incremental means update only new or changed data [OK]

Common Mistakes:

• Thinking incremental means reprocessing all data
• Confusing incremental with deleting old data
• Assuming incremental ignores changes

2.

Which Spark code snippet correctly filters new data for incremental processing?

df_new = df_all.filter(____)

easy

A. df_all.timestamp > last_processed_time

B. df_all.timestamp < last_processed_time

C. df_all.id == last_processed_id

D. df_all.date == '2020-01-01'

Solution

1. Step 1: Identify filtering condition for new data

   To get new data, filter rows with timestamp greater than last processed time.

2. Step 2: Match condition to options

   df_all.timestamp > last_processed_time uses > last_processed_time, which correctly selects new data.

3. Final Answer:

   df_all.timestamp > last_processed_time -> Option A

4. Quick Check:

   Filter new data by timestamp > last processed [OK]

Hint: Filter with timestamp greater than last processed time [OK]

Common Mistakes:

• Using less than instead of greater than
• Filtering by exact id instead of timestamp
• Filtering by unrelated fixed date

3.

Given this Spark code for incremental processing, what will df_incremental.count() output?

from pyspark.sql import SparkSession
spark = SparkSession.builder.getOrCreate()
data = [(1, '2024-01-01'), (2, '2024-01-02'), (3, '2024-01-03')]
df_all = spark.createDataFrame(data, ['id', 'date'])
last_processed_date = '2024-01-01'
df_incremental = df_all.filter(df_all.date > last_processed_date)
print(df_incremental.count())

medium

A. 2

B. 3

C. 1

D. 0

Solution

1. Step 1: Understand filtering condition

   Filter keeps rows where date > '2024-01-01'. Data has dates '2024-01-01', '2024-01-02', '2024-01-03'.

2. Step 2: Count rows matching condition

   Rows with dates '2024-01-02' and '2024-01-03' match, so count is 2.

3. Final Answer:

   2 -> Option A

4. Quick Check:

   Dates after '2024-01-01' = 2 rows [OK]

Hint: Count rows with date greater than last processed date [OK]

Common Mistakes:

• Including the date equal to last_processed_date
• Counting all rows instead of filtered
• Confusing greater than with less than

4.

Find the error in this Spark code for incremental processing:

df_incremental = df_all.filter(df_all.timestamp < last_processed_time)

Assuming last_processed_time is the timestamp of the last processed batch.

medium

A. The variable last_processed_time is undefined

B. The filter should use <= to include last processed data

C. The filter should use == to match last processed time

D. The filter should use > instead of < to get new data

Solution

1. Step 1: Understand filtering logic for incremental data

   Incremental processing requires filtering data newer than last processed time, so timestamp > last_processed_time.

2. Step 2: Identify incorrect operator

   The code uses < which selects older data, not new data.

3. Final Answer:

   The filter should use > instead of < to get new data -> Option D

4. Quick Check:

   New data filter uses > last processed time [OK]

Hint: New data means timestamp greater than last processed [OK]

Common Mistakes:

• Using less than instead of greater than
• Confusing equality with incremental filter
• Assuming variable is undefined without checking

5.

You have a Delta Lake table storing daily sales data. You want to update it incrementally with new data from a streaming source. Which approach is best?

hard

A. Delete the Delta table and recreate it daily

B. Use merge operation to upsert new and updated records into the Delta table

C. Append new data without checking for duplicates or updates

D. Overwrite the entire Delta table with new streaming data each time

Solution

1. Step 1: Understand Delta Lake incremental update capabilities

   Delta Lake supports merge to upsert (insert or update) records efficiently.

2. Step 2: Evaluate options for incremental update

   Use merge operation to upsert new and updated records into the Delta table uses merge, which handles new and changed data correctly. Others cause data loss or duplicates.

3. Final Answer:

   Use merge operation to upsert new and updated records into the Delta table -> Option B

4. Quick Check:

   Delta Lake incremental update = merge upsert [OK]

Hint: Use merge for incremental upsert in Delta Lake [OK]

Common Mistakes:

• Overwriting entire table loses old data
• Appending without deduplication causes duplicates
• Deleting table loses all history