Document versioning in Elasticsearch - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the version number after the update?

Given a document indexed with version 3, what will be the version number after a successful update using optimistic concurrency control with version 3?

Elasticsearch

PUT /my_index/_doc/1?version=3
{
  "field": "new value"
}

A 4

B 3

C 5

D Version conflict error

💡 Hint

When you update a document with the correct version, Elasticsearch increments the version.

Elasticsearch uses optimistic concurrency control. If you specify the current version (3) when updating, the update succeeds and the version increments to 4.

❓ Predict Output

intermediate

What happens if you update with an outdated version?

If a document currently has version 5, what happens when you try to update it specifying version 3?

Elasticsearch

PUT /my_index/_doc/1?version=3
{
  "field": "another value"
}

A Update succeeds and version becomes 6

B Update succeeds but version stays 5

C Elasticsearch ignores the version and updates anyway

D Update fails with a version conflict error

💡 Hint

Elasticsearch prevents updates if the version does not match the current document version.

When you specify a version lower than the current document version, Elasticsearch rejects the update with a version conflict error to avoid overwriting newer data.

🧠 Conceptual

advanced

How does Elasticsearch handle versioning with external versioning?

Which statement best describes how external versioning works in Elasticsearch?

A Elasticsearch automatically sets the version based on the timestamp of the update

B Elasticsearch ignores the version and always increments internally

C You provide the version number and Elasticsearch only updates if the provided version is higher than the current

D External versioning disables version checks and always overwrites the document

💡 Hint

External versioning lets you control the version number yourself.

With external versioning, you supply the version number. Elasticsearch updates the document only if the provided version is greater than the current version, ensuring your external system controls version order.

❓ Predict Output

advanced

What is the output of this version conflict scenario?

Consider this sequence: 1. Document version is 2. 2. Two concurrent updates try to update with version 2. What happens to the second update?

Elasticsearch

PUT /my_index/_doc/1?version=2
{
  "field": "update A"
}

PUT /my_index/_doc/1?version=2
{
  "field": "update B"
}

A Second update overwrites first without error

B First update succeeds, second update fails with version conflict

C Both updates fail with version conflict

D Both updates succeed and version becomes 4

💡 Hint

Only one update can succeed with the same version number.

The first update with version 2 succeeds and increments the version to 3. The second update still uses version 2, which is now outdated, so it fails with a version conflict error.

🧠 Conceptual

expert

Why is versioning important in Elasticsearch document updates?

Select the best reason why Elasticsearch uses versioning for documents.

A To prevent lost updates by ensuring only the latest changes overwrite older ones

B To allow multiple users to edit the same document simultaneously without conflicts

C To track the number of times a document has been read

D To automatically backup documents after each update

💡 Hint

Think about what happens if two updates happen at the same time.

Versioning helps Elasticsearch avoid lost updates by making sure that only updates with the correct or newer version overwrite the document, preventing older data from overwriting newer changes.

Practice

1. What is the main purpose of document versioning in Elasticsearch?

easy

A. To compress documents for storage efficiency

B. To prevent update conflicts by ensuring updates apply only to the expected document version

C. To increase the speed of document retrieval

D. To create backups of documents automatically

Solution

1. Step 1: Understand document versioning concept

   Document versioning is used to avoid conflicts when multiple updates happen simultaneously.

2. Step 2: Identify the main purpose

   It ensures updates only apply if the document is at the expected version, preventing overwriting newer changes.

3. Final Answer:

   To prevent update conflicts by ensuring updates apply only to the expected document version -> Option B

4. Quick Check:

   Versioning prevents conflicts = C [OK]

Hint: Versioning avoids conflicting updates by checking document version [OK]

Common Mistakes:

• Thinking versioning speeds up retrieval
• Confusing versioning with backup creation
• Assuming versioning compresses data

2. Which of the following is the correct way to specify a version when updating a document in Elasticsearch?

easy

A. POST /index/_update/1?version=3 { "doc": {"field": "value"} }

B. POST /index/_update/1 { "doc": {"field": "value"}, "version_number": 3 }

C. POST /index/_update/1 { "doc": {"field": "value"}, "ver": 3 }

D. POST /index/_update/1 { "doc": {"field": "value"}, "version": 3 }

Solution

1. Step 1: Recall Elasticsearch update syntax with version

   The version parameter is passed as a query parameter, not inside the JSON body.

2. Step 2: Identify correct syntax

   POST /index/_update/1?version=3 { "doc": {"field": "value"} } uses ?version=3 in the URL, which is the correct way to specify version for update.

3. Final Answer:

   POST /index/_update/1?version=3 { "doc": {"field": "value"} } -> Option A

4. Quick Check:

   Version is a query parameter, not in body [OK]

Hint: Use ?version=number in URL, not inside JSON body [OK]

Common Mistakes:

• Putting version inside JSON body
• Using wrong parameter names like ver or version_number
• Omitting the version parameter

3. Given the following update request, what will happen if the current document version is 5?

POST /myindex/_update/42?version=4
{
  "doc": {"status": "active"}
}

medium

A. The update will succeed and document version will become 5

B. The update will succeed but version will remain 4

C. The update will fail due to version conflict

D. The update will create a new document with version 4

Solution

1. Step 1: Check the version parameter against current document version

   The update request specifies version=4 but current version is 5.

2. Step 2: Understand version conflict behavior

   Elasticsearch rejects updates if the version does not match the current document version to avoid conflicts.

3. Final Answer:

   The update will fail due to version conflict -> Option C

4. Quick Check:

   Version mismatch causes update failure [OK]

Hint: Update only succeeds if version matches current document version [OK]

Common Mistakes:

• Assuming update succeeds despite version mismatch
• Thinking version resets after update
• Confusing version with document ID

4. You wrote this update request but it always fails with a version conflict error:

POST /products/_update/10?version=2
{
  "doc": {"price": 19.99}
}

What is the most likely cause?

medium

A. The update syntax is incorrect

B. The document with ID 10 does not exist

C. The field name 'price' is invalid

D. The current document version is not 2

Solution

1. Step 1: Understand version conflict error meaning

   Version conflict means the version specified does not match the document's current version.

2. Step 2: Check other options

   Document existence or field name errors cause different errors; syntax is correct here.

3. Final Answer:

   The current document version is not 2 -> Option D

4. Quick Check:

   Version conflict means version mismatch [OK]

Hint: Version conflict means your version number is outdated [OK]

Common Mistakes:

• Assuming document absence causes version conflict
• Blaming field names for version errors
• Ignoring correct syntax

5. You want to update a document only if it has not been changed since you last read it. Which approach correctly uses document versioning to achieve this?

hard

A. Fetch the document, note its version, then update using that version parameter

B. Update the document without specifying any version parameter

C. Use the document ID as the version parameter in the update request

D. Delete the document first, then create a new one with the updated data

Solution

1. Step 1: Understand optimistic concurrency control

   You must check the document's current version before updating to avoid overwriting changes.

2. Step 2: Apply versioning correctly

   Fetch the document, get its version, then update specifying that version to ensure no changes happened in between.

3. Final Answer:

   Fetch the document, note its version, then update using that version parameter -> Option A

4. Quick Check:

   Use version to update only if unchanged [OK]

Hint: Always update with the version you last read to avoid conflicts [OK]

Common Mistakes:

• Updating without version check causes silent overwrites
• Using document ID as version parameter
• Deleting instead of updating