Configuring Large Query Isolation

• Defining large queries:
  • The system checks the memory usage of all ongoing queries and flags queries that exceed a predefined memory usage threshold as large queries.
  • The system periodically checks the execution duration of all ongoing queries and flags queries that exceed a predefined duration threshold as large queries.
• Query cancellation policies:
  • fair: Determines which query to cancel by considering both memory usage and execution duration.
  • mem-first: Cancels the query that has the highest memory usage.
  • time-first: Cancels the query that has lasted the longest.
• Native cancel API: Elasticsearch's native cancel API can be used to cancel tasks, ensuring compatibility.

Only Elasticsearch 7.6.2 and 7.10.2 support large query isolation, which is enabled by default. The global timeout is disabled by default for large query isolation. You can enable and configure it via an API when necessary. Any change takes effect immediately.

Log in to Kibana and go to the command execution page. Elasticsearch clusters support multiple access methods. This topic uses Kibana as an example to describe the operation procedures.

1. Log in to the CSS management console.
2. In the navigation pane on the left, choose Clusters > Elasticsearch.
3. In the cluster list, find the target cluster, and click Kibana in the Operation column to log in to the Kibana console.
4. In the left navigation pane, choose Dev Tools.

   The left part of the console is the command input box, and the triangle icon in its upper-right corner is the execution button. The right part shows the execution result.

Large query isolation places large queries in an isolation pool, where they may be cancelled based on preset memory or duration thresholds. Large query isolation is enabled by default. You can modify this setting whenever necessary. Any change takes effect immediately.

1. Run the following command to enable or disable large query isolation:

   PUT _cluster/settings
   {
     "persistent": {
       "search.isolator.enabled": true
     }
   }
   
   

   Table 1 Setting large query isolation

   Parameter	Type	Default Value	Description
   search.isolator.enabled	Boolean	true	Whether to enable large query isolation. When enabled, large queries are managed separately from other normal queries. The value can be: true: Enable large query isolation. false: Disable large query isolation.

2. Run the following commands to configure thresholds that define large queries:

   PUT _cluster/settings
   {
     "persistent": {
       "search.isolator.memory.task.limit": "50MB",
       "search.isolator.time.management": "10s"
     }
   }
   
   

   Table 2 Parameters for configuring large query isolation thresholds

   Parameter	Type	Default Value	Description
   search.isolator.memory.task.limit	String	50MB	Large query memory threshold: When a query requests more memory than specified by this threshold, it is placed into an isolation pool. Value format: number + unit Number: a natural number Unit: B, K, KB, M, MB, G, GB, T, TB, P, or PB (case-insensitive) Minimum value: 0 (all queries are placed into the isolation pool) Maximum value: maximum node heap memory Lowering this value will cause more queries to be placed into the isolation pool, which will increase its memory usage. If you do lower this value, you should also increase the values of search.isolator.memory.pool.limit and search.isolator.count.limit, so that the isolation pool can hold more queries. This helps avoid triggering the circuit breaker mechanism due to resource exhaustion (for example, frequent query cancellation).
   search.isolator.time.management	String	10s	Large query execution duration threshold: When a query has lasted longer than specified by this threshold, it is placed into an isolation pool. Value format: number + unit Number: a natural number Unit: nanos (nanosecond), micros (microsecond), ms (millisecond), s (second), m (minute), h (hour), or d (day) Minimum value: 0 (all queries are placed into the isolation pool) Lowering this value will cause more queries to be placed into the isolation pool, which will increase its memory usage. If you do lower this value, you should also increase the values of search.isolator.memory.pool.limit and search.isolator.count.limit, so that the isolation pool can hold more queries. This helps avoid triggering the circuit breaker mechanism due to resource exhaustion (for example, frequent query cancellation).

3. Configure the isolation pool resource usage thresholds for triggering query cancellation.

   PUT _cluster/settings
   {
     "persistent": {
       "search.isolator.memory.pool.limit": "50%",
       "search.isolator.count.limit": 1000,
       "search.isolator.memory.heap.limit": "90%"
     }
   }
   
   

   Table 3 Parameters for configuring query cancellation thresholds

   Parameter	Type	Default Value	Description
   search.isolator.memory.pool.limit	String	50%	Maximum memory usage of the isolation pool as a percentage of the maximum node heap memory. When the total memory usage of large queries in the isolation pool exceeds this limit, the system cancels one of the large queries in the isolation pool based on a predefined policy to free resources and prevent memory overflow. Value range: 0.0–100.0% If your cluster primarily handles large queries (high memory usage or long execution time), increase this value. Meanwhile, set search.isolator.memory.task.limit and search.isolator.time.management accordingly to control the number of queries placed into the isolation pool.
   search.isolator.count.limit	Integer	1000	Maximum number of large queries allowed in the isolation pool. When this limit is reached, no more queries can be added to the isolation pool, preventing resource exhaustion. Value range: 10–50000 If your cluster primarily handles large queries (high memory usage or long execution time), increase this value. Meanwhile, set search.isolator.memory.task.limit and search.isolator.time.management accordingly to control the number of queries placed into the isolation pool.
   search.isolator.memory.heap.limit	String	90%	Node heap memory usage that triggers large query cancellation in the isolation pool. When this threshold is reached, the system cancels one of the large queries in the isolation pool based on a predefined policy to free resources and prevent memory overflow. Value range: 0.0–100.0% When indices.breaker.total.use_real_memory is enabled, this value must be lower than indices.breaker.total.limit. Otherwise, the native Elasticsearch circuit breaker will always be triggered first. For details, see Circuit breaker settings. If you anticipate traffic peaks or surges, you can lower this value to have the isolation pool's circuit breaker triggered earlier, thus preventing heap memory overload.

4. Run the following command to set the query cancellation policy:

   PUT _cluster/settings
   {
     "persistent": {
       "search.isolator.strategy": "fair",
       "search.isolator.strategy.ratio": "0.5%"
     }
   }
   
   

   Table 4 Parameters for configuring a query cancellation policy

   Parameter	Type	Default Value	Description
   search.isolator.strategy	String	fair	Policy for determining which query to cancel when query cancellation is triggered. fair (default): Determine which query to cancel by considering both memory usage and execution duration. If the difference between the memory usage of two candidate queries ≤ maximum Elasticsearch heap memory x fair policy threshold, the query that has a longer execution duration will be cancelled; on the contrary, if the difference is greater than that, the more memory-intensive query will be cancelled instead. Maximum Elasticsearch heap memory = min(31, total node memory/2) (GB). mem-first: Cancels the query that has the highest memory usage. time-first: Cancels the query that has lasted the longest. The large query isolation pool is checked every second until the heap memory is within a safe range.
   search.isolator.strategy.ratio	String	1%	Fair policy threshold. This is the ratio of the memory usage difference between two candidate queries in the isolation pool to the maximum node heap memory. When the memory usage difference between large queries in the isolation pool is small, the system preferentially cancels the query with the longest execution duration. Otherwise, it cancels the query with the highest memory usage. This parameter is valid only when search.isolator.strategy is set to fair. Value range: 0.0–100.0% You are advised to use the default value. Adjust only if necessary and with caution.

5. Run the following command to set the maximum number of cancelled query records retained in the large query isolation log:

   PUT _cluster/settings
   {
     "persistent": {
       "search.isolator.log.count": "100"
     }
   }
   
   

   Table 5 Parameter description

   Parameter	Type	Default Value	Description
   search.isolator.log.count	Integer	100	The maximum number of cancelled query records retained in the large query isolation log. The large query isolation log records cancelled large queries for query performance analysis and optimization. Once this limit is exceeded, the system automatically deletes the oldest records to control the log's memory footprint. Value range: 0–5000 Setting this value to 0 disables the large query isolation log.

   You can use the following APIs to query log information about cancelled queries:

   • Query statistics about cancelled queries on all nodes:

     GET /_isolator_metrics
     
     

   • Query statistics about cancelled queries on a specified node:

     GET /_isolator_metrics/{nodeId}
     
     

   • Query details about cancelled queries on all nodes:

     GET /_isolator_metrics?detailed
     
     

   • Query details about cancelled queries on a specified node:

     GET /_isolator_metrics/{nodeId}?detailed
     
     

   Table 6 Parameter description

   Parameter	Type	Default Value	Description
   node_id	String	N/A	Specifies one or more cluster nodes. Single node: Enter the node ID. Multiple nodes: Enter multiple node IDs and use a comma (,) to separate them. You can run the following command to obtain node IDs: GET _cat/nodes?s=n&h=n,id&v=true&full_id=true

   Example response:

   {
     "_nodes": {
       "total": 1,
       "successful": 1,
       "failed": 0
     },
     "cluster_name": "test",
     "nodes": {
       "CTqrZFXWTzmLonSZyNMKkQ": {
         "name": "test-ess-esn-1-1",
         "host": "172.16.101.116",
         "total_cancel": 0, //Total number of cancelled queries
         "isolator_cancel": 0,	//Number of queries cancelled because isolation pool thresholds were exceeded
         "out_of_time_cancel": 0	//Number of queries cancelled due to timeout
       }
     }
   }
   
   

When a global query timeout is configured, queries that exceed the specified duration are automatically cancelled, and the message "cancel cause by global time limit" is returned. This prevents long-running queries from consuming excessive resources. Global query timeout is disabled by default. You can modify this setting when necessary. Any change takes effect immediately.

Run the following command to enable and configure a global query timeout:

PUT _cluster/settings
{
  "persistent": {
    "search.isolator.time.enabled": true,
    "search.isolator.time.limit": "110s"
  }
}