Batch limits and retries in DynamoDB - Step-by-Step Execution

Concept Flow - Batch limits and retries

Start Batch Write

↓

Check Batch Size <= 25?

No→Split Batch

|Yes↓

Send Batch Request

↓

Receive Response

↓

Check Unprocessed Items?

No→Batch Complete

|Yes↓

Retry Unprocessed Items

↓

Send Batch Request

This flow shows how DynamoDB batch writes are limited to 25 items per request, and how unprocessed items are retried until all are written.

Execution Sample

DynamoDB

batch = items[:25]
while batch:
  response = dynamodb.batch_write_item(RequestItems={'YourTableName': batch})
  batch = response.get('UnprocessedItems', {}).get('YourTableName', [])
  if batch:
    wait_and_retry()

This code sends items in batches of max 25 to DynamoDB, retries unprocessed items until all are written.

Execution Table

Step	Batch Size	Action	Unprocessed Items	Retry?
1	25	Send batch write request	5	Yes
2	5	Retry unprocessed items	0	No
3	0	All items processed	-	No

💡 All items processed, no unprocessed items remain

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
batch	25 items	5 items (unprocessed)	0 items	0 items

Key Moments - 3 Insights

Why does DynamoDB limit batch writes to 25 items?

DynamoDB limits batch writes to 25 items per request to control load and ensure performance. See execution_table Step 1 where batch size is 25.

What happens to items not processed in the batch?

Unprocessed items are returned in the response and must be retried. In execution_table Step 1, 5 items were unprocessed and retried in Step 2.

Why do we retry only unprocessed items, not the whole batch?

Retrying only unprocessed items avoids duplicate writes and reduces load. The variable_tracker shows batch size shrinking after retries.

Visual Quiz - 3 Questions

Look at the execution_table, what is the batch size sent in Step 2?

A 30

B 5

C 25

D 0

💡 Hint

Check the 'Batch Size' column in execution_table row for Step 2

At which step does the batch become empty, indicating all items processed?

A Step 3

B Step 1

C Step 2

D None

💡 Hint

Look at the 'Batch Size' and 'Unprocessed Items' columns in execution_table

If the initial batch size was 50 items, how many batch requests would be needed at minimum?

A 3

B 1

C 2

D 25

💡 Hint

Recall the batch size limit of 25 items per request from concept_flow

Concept Snapshot

DynamoDB batch writes accept up to 25 items per request.
Unprocessed items are returned and must be retried.
Retries only include unprocessed items, not the whole batch.
This ensures efficient, reliable batch writing.
Always check response for unprocessed items and retry accordingly.

Full Transcript

This visual execution shows how DynamoDB batch write operations handle limits and retries. Each batch can contain up to 25 items. If the batch is larger, it is split. After sending a batch write request, DynamoDB may return some items as unprocessed due to capacity or throttling. These unprocessed items must be retried until all are written. The execution table traces batch sizes and retries step-by-step, showing how the batch shrinks as unprocessed items are retried. Key moments clarify why the limit exists, how unprocessed items are handled, and why retries focus only on those items. The quiz tests understanding of batch sizes, retry steps, and request counts. The snapshot summarizes the core rules for batch limits and retries in DynamoDB.