1. Slow Query Performance

Understanding the Issue

Queries take longer than expected, leading to application slowdowns.

Root Causes

• Scanning instead of querying the table.
• Indexes not optimized for query patterns.
• High read contention due to partitioning.

Fix

Use queries instead of scans to improve efficiency:

aws dynamodb query --table-name Orders --key-condition-expression "customerId = :id" --expression-attribute-values '{":id":{"S":"12345"}}'

Ensure Global Secondary Indexes (GSI) match query patterns:

aws dynamodb create-global-secondary-index --table-name Orders --index-name CustomerIndex --key-schema AttributeName=customerId,KeyType=HASH

2. Provisioned Throughput Exceeded

Understanding the Issue

DynamoDB throttles requests due to exceeding provisioned read/write capacity.

Root Causes

• Insufficient read/write capacity settings.
• High concurrent requests on a single partition.
• Misconfigured auto-scaling policies.

Fix

Enable on-demand capacity mode for variable workloads:

aws dynamodb update-table --table-name Orders --billing-mode PAY_PER_REQUEST

Use exponential backoff retries for throttled requests:

import boto3
import time

def retry_dynamodb_request():
    client = boto3.client("dynamodb")
    for i in range(5):
        try:
            response = client.get_item(TableName="Orders", Key={"orderId": {"S": "12345"}})
            return response
        except client.exceptions.ProvisionedThroughputExceededException:
            time.sleep(2 ** i)  # Exponential backoff

3. Inconsistent Reads

Understanding the Issue

Reads return outdated data instead of the latest changes.

Root Causes

• By default, DynamoDB performs eventually consistent reads.
• Replication lag in multi-region setups.
• High write contention causing delays in visibility.

Fix

Use strongly consistent reads for real-time data requirements:

aws dynamodb get-item --table-name Orders --key '{"orderId": {"S": "12345"}}' --consistent-read

Monitor and optimize write throughput to reduce lag:

aws dynamodb describe-table --table-name Orders

4. Access Denied Errors

Understanding the Issue

Applications or users cannot perform read/write operations on DynamoDB tables.

Root Causes

• Incorrect IAM policies assigned to users or roles.
• Missing permissions in the AWS resource policy.
• Restricted VPC endpoint policies blocking access.

Fix

Grant correct permissions to IAM roles:

{
  "Effect": "Allow",
  "Action": [
    "dynamodb:GetItem",
    "dynamodb:PutItem"
  ],
  "Resource": "arn:aws:dynamodb:us-east-1:123456789012:table/Orders"
}

Check VPC endpoint policies if using private connectivity:

aws ec2 describe-vpc-endpoints

5. Data Modeling Inefficiencies

Understanding the Issue

Tables are inefficiently designed, leading to excessive partition scans.

Root Causes

• Using multiple tables instead of a single table with indexes.
• Improper selection of partition keys.
• Large item sizes increasing storage and retrieval costs.

Fix

Use a single-table design with composite keys for better query performance:

aws dynamodb create-table --table-name Orders --attribute-definitions AttributeName=customerId,AttributeType=S AttributeName=orderId,AttributeType=S --key-schema AttributeName=customerId,KeyType=HASH AttributeName=orderId,KeyType=RANGE

Optimize item sizes by storing large payloads in S3 and referencing them in DynamoDB:

{
  "orderId": "12345",
  "receiptUrl": "s3://my-bucket/receipts/12345.pdf"
}

Conclusion

Amazon DynamoDB is a scalable and efficient NoSQL database, but troubleshooting slow queries, throughput limits, inconsistent reads, access control issues, and data modeling inefficiencies is crucial for optimal performance. By designing efficient table structures, optimizing access patterns, and managing permissions effectively, users can maximize the benefits of DynamoDB.

FAQs

1. Why are my DynamoDB queries slow?

Ensure you are using query instead of scan, optimize indexing, and distribute read traffic across partitions.

2. How do I fix DynamoDB throughput exceeded errors?

Enable on-demand capacity mode, implement exponential backoff retries, and use efficient key distribution.

3. How can I ensure strong consistency in DynamoDB reads?

Use the --consistent-read option and monitor write throughput for replication lag.

4. Why is my DynamoDB table returning access denied errors?

Verify IAM policies, ensure correct role permissions, and check VPC endpoint access settings.

5. What is the best way to model data in DynamoDB?

Use a single-table design with composite keys, optimize partition keys, and store large payloads in S3.