Async search for expensive queries in Elasticsearch - Step-by-Step Execution

Concept Flow - Async search for expensive queries

Start Async Search Request

↓

Elasticsearch Accepts Request

↓

Query Runs in Background

↓

Client Polls for Results

↓

Results Ready?

No→Wait and Poll Again

Yes↓

Client Retrieves Results

↓

Process or Display Results

↓

End

The client sends an async search request, Elasticsearch runs the query in the background, the client polls until results are ready, then retrieves and processes them.

Execution Sample

Elasticsearch

POST /_async_search
{
  "query": { "match_all": {} },
  "size": 1000
}

Starts an async search that matches all documents and returns up to 1000 results.

Execution Table

Step	Action	Request/Response	Status	Notes
1	Send async search request	POST /_async_search with query	Accepted	Elasticsearch starts query in background
2	Receive async search ID	{ "id": "abc123", "is_running": true }	Running	Client gets search ID to poll later
3	Poll for results	GET /_async_search/abc123	Running	Query still running, no results yet
4	Poll again after wait	GET /_async_search/abc123	Completed	Results ready, returned in response
5	Process results	Response contains hits	Success	Client processes or displays results
6	Delete async search	DELETE /_async_search/abc123	Deleted	Clean up resources on server

💡 Execution stops after results are retrieved and optionally deleted.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 4	Final
search_id	null	"abc123"	"abc123"	"abc123"	null
is_running	null	true	true	false	false
results	null	null	null	hits data	hits data

Key Moments - 3 Insights

Why do we get a search ID instead of immediate results?

Because the query is expensive, Elasticsearch runs it in the background and returns a search ID to let the client check back later, as shown in execution_table step 2.

What happens if we poll too early for results?

The response will indicate the search is still running (step 3), so the client must wait and poll again later.

Why should we delete the async search after retrieving results?

Deleting frees server resources used to keep the search context, as shown in step 6 of the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, what is the status after the first async search request is sent?

A Completed

B Accepted

C Deleted

D Failed

💡 Hint

Check the Status column at Step 1 in the execution_table.

At which step does the client receive the actual search results?

A Step 4

B Step 3

C Step 2

D Step 6

💡 Hint

Look for 'Results ready' in the Notes column of the execution_table.

If the client never deletes the async search, what variable in variable_tracker remains non-null?

A results

B is_running

C search_id

D null

💡 Hint

Check the 'search_id' row in variable_tracker and what happens after Step 6.

Concept Snapshot

Async search lets Elasticsearch run expensive queries in background.
Client sends request and gets a search ID.
Client polls with ID until results are ready.
Results returned when complete.
Delete async search to free resources.

Full Transcript

Async search in Elasticsearch helps run heavy queries without waiting for immediate results. The client sends a request and gets back a search ID. Elasticsearch runs the query in the background. The client polls using the ID to check if results are ready. Once ready, the client retrieves and processes the results. Finally, the client can delete the async search to clean up resources. This process avoids long waits and keeps the system responsive.