Error log: This is a root_cause in a search query error response, typically when using a terms query with a very large array.
JSON
None
{
"error": {
"root_cause": [
{
"type": "illegal_state_exception",
"reason": "Failed to execute phase [query]",
"caused_by": {
"type": "too_many_clauses",
"reason": "max_clause_count is set to 1024"
}
}
],
"type": "search_phase_execution_exception",
// ...
},
"status": 500
}Why… is this happening? This is a safety limit inside Lucene (the engine that powers OpenSearch). When you run certain queries, like a terms query (e.g., “find all documents where user_id is one of [1, 2, 3, … 5000]”), Lucene expands this into a “Boolean query” (e.g., user_id=1 OR user_id=2 OR ...).
To prevent a single query with millions of OR clauses from consuming all CPU and memory, Lucene has a hard limit on the maximum number of clauses allowed in a single Boolean query. By default, that limit is 1024.
Your query (likely a terms query with more than 1024 items) has exceeded this limit.
Best practice:
1. Reduce the number of terms: The best fix is to change your application logic. Can you break the query into several smaller requests? (e.g., 5 requests of 1000 terms each).
2. Use the terms_lookup feature: If your list of terms is in another index, you can use a terms_lookup. This tells OpenSearch to fetch the terms from a document instead of you sending them all.
3. Increase the limit (not recommended): You can increase this limit, but do so with extreme caution. This can easily lead to slow queries and cluster instability. If you must, you can change it per-index:
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PUT /my-index/_settings
{
"index.query.bool.max_clause_count": 2048
}4. Changing this dynamically for the whole cluster is deprecated and not advised.
What else can I do? Trying to figure out the best way to query against a large list of IDs? This is a common design question. Ask the OpenSearch community for patterns like terms_lookup or _msearch. For direct help, contact us in The OpenSearch Slack Channel in #General.
