# OOM Protection Using Automatic Query Killing Pinot has implemented a mechanism to monitor the total jvm heap size and per query memory allocation approximation for server (see ). If enabled, this mechanism can help to protect the server from OOM caused by expensive queries (e.g. distinctcount + group by on high cardinality columns). Upon an immediate risk of heap depletion, this mechanism will kick in and kill from the most expensive query(s). Here are the server configurations: | Config | Default | Description | | ------------------------------------------------------------------- | ----------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | pinot.query.scheduler.accounting.factory.name | `DefaultThreadResourceUsageAccountant` which only hardens timeout but no preemption | Use `org.apache.pinot.core.accounting.PerQueryCPUMemAccountantFactory`If one intend to enable this feature | | pinot.query.scheduler.accounting.enable.thread.memory.sampling | false | Account for threads' memory usage of a query, works only for hotspot jvm. If enabled, the killing decision will be based on memory allocated. | | pinot.query.scheduler.accounting.enable.thread.cpu.sampling | false | Account for threads' cpu time of a query. If memory sampling is disabled/unavailable, the killing decision will be based on CPU time. If both are disabled, the framework will not able to pick the most expensive query. | | pinot.query.scheduler.accounting.oom.enable.killing.query | false | Whether the framework will actually commit to kill queries. If disabled, only error message will be logged. | | pinot.query.scheduler.accounting.publishing.jvm.heap.usage | false | Whether the framework periodically publishes the heap usage to Pinot metrics. | | pinot.query.scheduler.accounting.oom.panic.heap.usage.ratio | 0.99 | When the heap usage exceeds this ratio, the frame work will kill all the queries. This can be set to be >1 to prevent a full killing from happening. | | pinot.query.scheduler.accounting.oom.critical.heap.usage.ratio | 0.96 | When the heap usage exceeds this ratio, the frame work will kill the most expensive query. | | pinot.query.scheduler.accounting.oom.alarming.heap.usage.ratio | 0.75 | When the heap usage exceeds this ratio, the framework will run more frequently to gather stats and prepare to kill queries timely. | | pinot.query.scheduler.accounting.sleep.ms | 30ms | The periodical task for query killing wakes up every 30ms | | pinot.query.scheduler.accounting.sleep.time.denominator | 3 (corresponding to 10ms sleep time at alarming level heap usage) |

When the heap usage exceeds this alarming level, the sleep time will be
sleepTime/denominator

| | pinot.query.scheduler.accounting.min.memory.footprint.to.kill.ratio | 0.025 | If a query allocates memory below this ratio of total heap size (Xmx) it will not be killed. This is to prevent aggressive killing when the heap memory is not mainly allocated for queries | | pinot.query.scheduler.accounting.gc.backoff.count | 5 | When the framework consecutively kills this many expensive queries it will explicitly trigger gc to reclaim the memory. | --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.pinot.apache.org/release-1.1.0/for-operators/operating-pinot/oom-protection-using-automatic-query-killing.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.