[Solved] A developer wrote this code for write sharding:shard_id = hash(user_id) % 3 partition_key = f"user#{user_id}#shard{shard_id}" But writes are failing with validation errors. What is the likely problem? | DynamoDB

DynamoDB - Access Patterns and Query Optimization

A developer wrote this code for write sharding:

shard_id = hash(user_id) % 3
partition_key = f"user#{user_id}#shard{shard_id}"

But writes are failing with validation errors. What is the likely problem?

AShard ID must be a string, not an integer.

BThe hash function is not supported by DynamoDB.

CThe table does not support composite keys.

DThe partition key contains invalid characters or format.

Step-by-Step Solution

Solution:

Step 1: Check partition key format
DynamoDB partition keys must be strings without unsupported characters; the format "user#...#shard..." is valid if all parts are strings.
Step 2: Identify validation error cause
If shard_id is an integer, concatenation with string using f-string is valid, but if any invalid characters or empty parts exist, validation fails.
Final Answer:
The partition key contains invalid characters or format. -> Option D
Quick Check:
Partition key format errors cause validation failures [OK]

Quick Trick: Check partition key format for invalid chars [OK]

Common Mistakes:

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A developer wrote this code for write sharding: