Cache management (query, request, field data) in Elasticsearch - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to enable query cache in Elasticsearch.

Elasticsearch

{
  "query": {
    "match_all": {}
  },
  "[1]": true
}

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

Aquery_cache

Brequest_cache

Ccache_enabled

Dfielddata_cache

Attempts:

3 left

💡 Hint

Common Mistakes

Using request_cache instead of query_cache

Using fielddata_cache which is for field data, not queries

Using a non-existent setting like cache_enabled

The query_cache setting enables caching of query results in Elasticsearch.

2fill in blank

medium

Complete the code to enable request cache for a search request.

Elasticsearch

{
  "size": 10,
  "query": {
    "term": { "user": "kimchy" }
  },
  "[1]": true
}

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

Aquery_cache

Bfielddata_cache

Crequest_cache

Dcache_query

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing request_cache with query_cache

Using fielddata_cache which is unrelated to request caching

Using incorrect setting names

The request_cache setting enables caching of the entire search request response.

3fill in blank

hard

Fix the error in the field data cache setting to enable it correctly.

Elasticsearch

{
  "fielddata": {
    "[1]": true
  }
}

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

Aenable

Bfielddata_cache

Ccache

Dfielddata

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'cache' or 'fielddata_cache' which are invalid keys

Using 'fielddata' again inside the fielddata object

The correct setting to enable field data cache is enable inside the fielddata object.

4fill in blank

hard

Fill both blanks to create a query that uses request cache and disables query cache.

Elasticsearch

{
  "query": {
    "match": { "title": "Elasticsearch" }
  },
  "[1]": false,
  "[2]": true
}

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

Aquery_cache

Brequest_cache

Cfielddata_cache

Dcache_enabled

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the cache names

Using invalid cache names

Setting both caches to true or false

Setting query_cache to false disables query caching, while setting request_cache to true enables request caching.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that caches field lengths greater than 5.

Elasticsearch

{
  "field_lengths_cache": {
    "lengths": {word: len(word) for word in words if len(word) [1] [2],
    "[3]": true
  }
}

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

A>

B5

Ccache_enabled

Drequest_cache

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong comparison operators

Using wrong cache keys

Forgetting to enable the cache

The comprehension filters words with length greater than 5 using > and 5. The cache is enabled with cache_enabled.

Practice

1. What is the primary purpose of cache management in Elasticsearch?

easy

A. To store recent search data and speed up query responses

B. To permanently save all search results for future use

C. To delete all data from the Elasticsearch index

D. To increase the size of the Elasticsearch cluster automatically

Solution

1. Step 1: Understand what cache does in Elasticsearch

   Cache temporarily stores recent search data to avoid repeating expensive operations.

2. Step 2: Identify the main benefit of caching

   By storing recent data, Elasticsearch can respond faster to repeated queries.

3. Final Answer:

   To store recent search data and speed up query responses -> Option A

4. Quick Check:

   Cache speeds up queries = A [OK]

Hint: Cache is for speed, not permanent storage [OK]

Common Mistakes:

• Thinking cache saves data permanently
• Confusing cache with index storage
• Assuming cache increases cluster size

2. Which of the following is the correct syntax to clear the query cache for an index named products using Elasticsearch REST API?

easy

A. POST /products/_cache/clear?query=true

B. POST /products/_cache/clear/query

C. POST /products/_cache/clear/fielddata

D. POST /products/_clear_cache/query

Solution

1. Step 1: Recall the correct REST API endpoint for clearing cache

   Elasticsearch uses _cache/clear with query parameters to specify cache types.

2. Step 2: Identify the correct parameter for query cache

   The query cache is cleared by adding ?query=true to the endpoint.

3. Final Answer:

   POST /products/_cache/clear?query=true -> Option A

4. Quick Check:

   Use query=true parameter to clear query cache [OK]

Hint: Use query=true parameter to clear query cache [OK]

Common Mistakes:

• Using wrong endpoint like _clear_cache
• Confusing fielddata cache with query cache
• Missing query parameter in URL

3. Given this Elasticsearch request to clear caches:

POST /myindex/_cache/clear
{
  "fielddata": true,
  "query": true
}

What caches will be cleared?

medium

A. Only the query cache

B. Only the fielddata cache

C. Request cache only

D. Both query and fielddata caches

Solution

1. Step 1: Analyze the JSON body parameters

   The request sets both fielddata and query to true, indicating both caches should be cleared.

2. Step 2: Understand cache clearing behavior

   When multiple cache types are true, Elasticsearch clears all specified caches.

3. Final Answer:

   Both query and fielddata caches -> Option D

4. Quick Check:

   fielddata=true + query=true clears both caches [OK]

Hint: True flags clear all specified caches together [OK]

Common Mistakes:

• Assuming only one cache clears at a time
• Confusing request cache with fielddata cache
• Ignoring JSON body parameters

4. You run this command to clear the request cache:

POST /logs/_cache/clear
{
  "request": true
}

But the cache is not cleared. What is the likely problem?

medium

A. The index name logs is invalid for cache clearing

B. The syntax is incorrect; request cache cannot be cleared this way

C. Request cache is disabled by default and must be enabled first

D. You must specify fielddata as true to clear request cache

Solution

1. Step 1: Understand request cache behavior

   Request cache is off by default and must be enabled in index settings to be used and cleared.

2. Step 2: Identify why clearing fails

   If request cache is disabled, clearing it has no effect, so the command appears to do nothing.

3. Final Answer:

   Request cache is disabled by default and must be enabled first -> Option C

4. Quick Check:

   Request cache off by default = no clearing effect [OK]

Hint: Enable request cache before clearing it [OK]

Common Mistakes:

• Assuming request cache is always enabled
• Using wrong syntax to clear caches
• Thinking fielddata cache affects request cache

5. You want to optimize Elasticsearch performance by managing caches. Which strategy correctly balances cache clearing and system stability?

hard

A. Clear all caches frequently to free memory, even during heavy query load

B. Clear query and request caches during low traffic, and monitor fielddata cache size

C. Never clear caches to keep all data in memory permanently

D. Disable all caches to avoid stale data and improve stability

Solution

1. Step 1: Understand cache clearing impact

   Clearing caches frees memory but can slow queries if done too often or during heavy load.

2. Step 2: Identify best practice for cache management

   Clearing query and request caches during low traffic avoids performance hits; monitoring fielddata cache prevents memory issues.

3. Final Answer:

   Clear query and request caches during low traffic, and monitor fielddata cache size -> Option B

4. Quick Check:

   Clear caches smartly during low load + monitor fielddata [OK]

Hint: Clear caches during low load, monitor fielddata size [OK]

Common Mistakes:

• Clearing caches too often during heavy load
• Disabling caches completely
• Ignoring fielddata cache memory use