Item size limits and considerations in DynamoDB - Step-by-Step Execution

Concept Flow - Item size limits and considerations

Start: Create/Update Item

↓

Calculate Item Size

↓

Is size <= 400 KB?

No→Reject Item: Too Large

Yes↓

Store Item in Table

↓

Item Stored Successfully

When adding or updating an item, DynamoDB calculates its size. If the size is more than 400 KB, the item is rejected. Otherwise, it is stored successfully.

Execution Sample

DynamoDB

PutItem {"id": "123", "data": "...large string..."}
Calculate size of item
If size > 400 KB reject
Else store item

This simulates adding an item and checking if its size is within the 400 KB limit before storing.

Execution Table

Step	Action	Item Size (KB)	Condition	Result
1	Receive item with id and data	N/A	N/A	Proceed to size calculation
2	Calculate item size	350	350 <= 400?	Yes, proceed to store
3	Store item in table	350	N/A	Item stored successfully
4	Receive item with id and data	N/A	N/A	Proceed to size calculation
5	Calculate item size	450	450 <= 400?	No, reject item
6	Reject item	450	N/A	Item rejected due to size limit

💡 Execution stops when item size exceeds 400 KB and item is rejected.

Variable Tracker

Variable	Start	After Step 2	After Step 3 or 6
item_size_kb	N/A	350	350 (stored)
item_size_kb	N/A	450	450 (rejected)

Key Moments - 2 Insights

Why is the item rejected even though it has valid data?

Because the item size exceeds 400 KB as shown in execution_table row 5, DynamoDB rejects it to enforce the size limit.

Does DynamoDB count only attribute values for size or the whole item?

DynamoDB counts the entire item size including attribute names and values, as implied in step 2 where total item size is calculated.

Visual Quiz - 3 Questions

Look at the execution_table, what is the item size at step 2 for the first item?

A 400 KB

B 350 KB

C 450 KB

D N/A

💡 Hint

Check the 'Item Size (KB)' column at step 2 in the execution_table.

At which step does the item get rejected due to size?

A Step 6

B Step 5

C Step 3

D Step 2

💡 Hint

Look for the row where the result says 'Item rejected due to size limit' in execution_table.

If the item size was exactly 400 KB, what would happen according to the flow?

A Item would be rejected

B Item size is recalculated

C Item would be stored

D Item is partially stored

💡 Hint

Refer to the condition 'Is size <= 400 KB?' in concept_flow and execution_table step 2.

Concept Snapshot

DynamoDB items must be 400 KB or less in size.
Item size includes attribute names and values.
If item size > 400 KB, DynamoDB rejects the item.
Check item size before storing to avoid errors.
This limit applies to each individual item stored.

Full Transcript

When you add or update an item in DynamoDB, it calculates the total size of that item including all attribute names and values. If the size is more than 400 KB, DynamoDB will reject the item and not store it. If the size is 400 KB or less, the item is stored successfully. This ensures that items do not exceed the maximum allowed size. For example, if an item has a size of 350 KB, it will be stored. But if it has 450 KB, it will be rejected. Always check your item size before storing to avoid errors.