Batch limits and best practices in Firebase - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the maximum number of operations allowed in a single Firestore batch write?

A single Firestore batch write can include up to 500 operations.

beginner

Why should you avoid very large batch writes in Firestore?

Very large batch writes can cause delays, increase the chance of failures, and make error handling harder. It's better to keep batches small and manageable.

intermediate

What is a good practice when handling batch write failures in Firebase?

Retry only the failed batch or operations, and implement exponential backoff to avoid overwhelming the server.

intermediate

How can you improve performance when writing many documents in Firestore?

Split writes into multiple batches of 500 or fewer operations and run them in parallel if possible.

beginner

What happens if you exceed the batch write limit in Firestore?

The batch write will fail with an error, and no operations in that batch will be applied.

What is the maximum number of operations allowed in a Firestore batch write?

A 500

B 1000

C 200

D 50

Firestore batch writes support up to 500 operations per batch.

What is a recommended way to handle batch write failures?

A Split the batch into single operations and retry all

B Ignore the failure and continue

C Retry the entire batch immediately without delay

D Retry failed operations with exponential backoff

Retrying failed operations with exponential backoff helps avoid overwhelming the server.

Why should you split large writes into smaller batches?

A To avoid writing duplicate data

B Because Firestore charges less for smaller batches

C To reduce the chance of failure and improve performance

D Because Firestore does not support batch writes

Smaller batches reduce failure risk and can be processed faster.

What happens if a batch write exceeds the limit?

A The batch fails and no operations are applied

B The batch partially succeeds

C The batch is automatically split

D The batch is queued for later

Firestore rejects the entire batch if it exceeds the operation limit.

How can you improve throughput when writing many documents?

A Write documents one by one sequentially

B Split writes into multiple batches and run them in parallel

C Write all documents in one large batch

D Use transactions instead of batch writes

Parallel batches improve throughput while respecting limits.

Explain the batch write limits in Firestore and why they matter.

Think about how many operations you can group safely.

Describe best practices for handling large numbers of writes in Firebase.

Consider performance and error handling.

Practice

1. What is the maximum number of operations allowed in a single Firestore batch write?

easy

A. Unlimited operations

B. 1000 operations

C. 200 operations

D. 500 operations

Solution

1. Step 1: Recall Firestore batch write limits

   Firestore limits batch writes to a maximum of 500 operations to ensure performance and consistency.

2. Step 2: Confirm the exact number

   The official Firestore documentation states the limit is 500 operations per batch.

3. Final Answer:

   500 operations -> Option D

4. Quick Check:

   Batch limit = 500 operations [OK]

Hint: Remember Firestore batch max is 500 ops per batch [OK]

Common Mistakes:

• Thinking batch limit is 1000 or unlimited
• Confusing batch limit with document size limit
• Assuming batch size depends on network speed

2. Which of the following is the correct way to start a batch write in Firestore using JavaScript?

easy

A. const batch = firestore.startBatch();

B. const batch = firestore.batch();

C. const batch = new firestore.BatchWrite();

D. const batch = firestore.createBatchWrite();

Solution

1. Step 1: Identify Firestore batch syntax

   The Firestore JavaScript SDK uses firestore.batch() to create a new batch instance.

2. Step 2: Verify method names

   Methods like startBatch(), BatchWrite(), or createBatchWrite() do not exist in Firestore SDK.

3. Final Answer:

   const batch = firestore.batch(); -> Option B

4. Quick Check:

   Correct batch start method = batch() [OK]

Hint: Use firestore.batch() to start batch writes [OK]

Common Mistakes:

• Using non-existent methods like startBatch()
• Trying to instantiate batch with new keyword
• Confusing batch with transaction methods

3. Consider this code snippet in Firestore JavaScript SDK:

const batch = firestore.batch();
const docRef1 = firestore.collection('users').doc('user1');
const docRef2 = firestore.collection('users').doc('user2');
batch.set(docRef1, {name: 'Alice'});
batch.update(docRef2, {age: 30});
await batch.commit();
console.log('Batch committed');

What will be printed after successful execution?

medium

A. Batch committed

B. Error: update failed

C. No output

D. Batch commit pending

Solution

1. Step 1: Understand batch commit behavior

   Calling await batch.commit() waits for all operations to complete successfully.

2. Step 2: Confirm console output after commit

   After commit resolves, console.log prints 'Batch committed'. No errors occur if data is valid.

3. Final Answer:

   Batch committed -> Option A

4. Quick Check:

   Successful commit logs 'Batch committed' [OK]

Hint: Await batch.commit() before logging success message [OK]

Common Mistakes:

• Expecting output before commit finishes
• Assuming update fails without checking document existence
• Ignoring async/await behavior

4. You try to batch write 600 operations in Firestore but get an error. What is the best way to fix this?

medium

A. Split the 600 operations into two batches of 300 each

B. Increase Firestore batch limit in settings

C. Write all 600 operations in one batch anyway

D. Use a transaction instead of batch

Solution

1. Step 1: Recognize Firestore batch limit

   Firestore limits batch writes to 500 operations max, so 600 exceeds this limit causing errors.

2. Step 2: Apply best practice to split batches

   Splitting 600 operations into smaller batches (e.g., two batches of 300) avoids limit errors and keeps writes manageable.

3. Final Answer:

   Split the 600 operations into two batches of 300 each -> Option A

4. Quick Check:

   Split large batches to ≤ 500 ops [OK]

Hint: Split batches over 500 ops into smaller chunks [OK]

Common Mistakes:

• Trying to increase batch limit (not possible)
• Ignoring batch size causing runtime errors
• Using transactions which have different limits

5. You have 1200 user records to update in Firestore. Which approach follows best practices for batch writes?

hard

A. Update users one by one without batching

B. Send all 1200 updates in a single batch to save time

C. Divide updates into 3 batches of 400 operations each and commit sequentially

D. Use a single transaction for all 1200 updates

Solution

1. Step 1: Understand Firestore batch and transaction limits

   Batch writes are limited to 500 operations; transactions have similar or stricter limits.

2. Step 2: Apply best practice for large updates

   Dividing 1200 updates into smaller batches (e.g., 3 batches of 400) avoids limit errors and ensures reliable commits.

3. Step 3: Avoid single large batch or single transaction

   Sending all 1200 in one batch or transaction exceeds limits and risks failure; updating one by one is inefficient.

4. Final Answer:

   Divide updates into 3 batches of 400 operations each and commit sequentially -> Option C

5. Quick Check:

   Split large updates into batches ≤ 500 ops [OK]

Hint: Split large updates into batches under 500 ops [OK]

Common Mistakes:

• Trying to batch all 1200 updates at once
• Using transactions for very large writes
• Updating records one by one causing slow performance