Batch limits and best practices in Firebase - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a batch write in Firebase.

Firebase

const batch = db.[1]();

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AwriteBatch

Bbatch

CstartBatch

DbeginBatch

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'startBatch' or 'beginBatch' which do not exist.

Using 'batch' directly without 'writeBatch()'.

In Firebase, writeBatch() is used to create a batch write object.

2fill in blank

medium

Complete the code to commit the batch write.

Firebase

await batch.[1]();

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Aapply

Bcommit

Csend

Dexecute

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'execute' or 'send' which are not Firebase batch methods.

Forgetting to await the commit.

The commit() method sends all the writes in the batch to the database.

3fill in blank

hard

Fix the error in the code to add a document write to the batch.

Firebase

batch.set(docRef, [1]);

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Aname = 'Alice'

B['name', 'Alice']

C'name: Alice'

D{ name: 'Alice' }

Attempts:

3 left

💡 Hint

Common Mistakes

Passing data as a string or array instead of an object.

Using assignment syntax inside the data parameter.

The data must be an object with key-value pairs, like { name: 'Alice' }.

4fill in blank

hard

Fill both blanks to limit batch size and handle errors.

Firebase

if (batchSize [1] MAX_BATCH_SIZE) {
  await batch.[2]();
  batch = db.writeBatch();
  batchSize = 0;
}

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A>=

Bcommit

C<=

Dexecute

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<=' instead of '>=' for the size check.

Using 'execute()' which is not a Firebase batch method.

Check if batch size is greater or equal to max, then commit the batch.

5fill in blank

hard

Fill all three blanks to create a safe batch write loop.

Firebase

for (const item of items) {
  const docRef = db.collection('users').doc(item.id);
  batch.[1](docRef, item.data);
  batchSize [2] 1;
  if (batchSize [3] MAX_BATCH_SIZE) {
    await batch.commit();
    batch = db.writeBatch();
    batchSize = 0;
  }
}
await batch.commit();

Drag options to blanks, or click blank then click option'

Aset

B+=

C>=

Dupdate

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'update' instead of 'set' which may fail if document does not exist.

Using '=' instead of '+=' to increment batchSize.

Using '<=' instead of '>=' in the batch size check.

Use set to add writes, increment batchSize with +=, and check if batchSize is greater or equal to max.

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