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95 lines
5.3 KiB
Markdown
95 lines
5.3 KiB
Markdown
---
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layout: doc_page
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title: "Indexer Process"
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---
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> The Indexer is an optional and [experimental](../development/experimental.md) feature.
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> Its memory management system is still under development and will be significantly enhanced in later releases.
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The Apache Druid Indexer process is an alternative to the MiddleManager + Peon task execution system. Instead of forking a separate JVM process per-task, the Indexer runs tasks as separate threads within a single JVM process.
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The Indexer is designed to be easier to configure and deploy compared to the MiddleManager + Peon system and to better enable resource sharing across tasks.
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### Configuration
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For Apache Druid Indexer Process Configuration, see [Indexer Configuration](../configuration/index.md#indexer).
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### HTTP endpoints
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The Indexer process shares the same HTTP endpoints as the [MiddleManager](../operations/api-reference.md#middlemanager).
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### Running
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```
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org.apache.druid.cli.Main server indexer
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```
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### Task resource sharing
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The following resources are shared across all tasks running inside an Indexer process.
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#### Query resources
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The query processing threads and buffers are shared across all tasks. The Indexer will serve queries from a single endpoint shared by all tasks.
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If [query caching](../configuration/index.md#indexer-caching) is enabled, the query cache is also shared across all tasks.
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#### Server HTTP threads
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The Indexer maintains two equally sized pools of HTTP threads.
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One pool is exclusively used for task control messages between the Overlord and the Indexer ("chat handler threads"). The other pool is used for handling all other HTTP requests.
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The size of the pools are configured by the `druid.server.http.numThreads` configuration (e.g., if this is set to 10, there will be 10 chat handler threads and 10 non-chat handler threads).
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In addition to these two pools, 2 separate threads are allocated for lookup handling. If lookups are not used, these threads will not be used.
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#### Memory sharing
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The Indexer uses the `druid.worker.globalIngestionHeapLimitBytes` configuration to impose a global heap limit across all of the tasks it is running.
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This global limit is evenly divided across the number of task slots configured by `druid.worker.capacity`.
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To apply the per-task heap limit, the Indexer will override `maxBytesInMemory` in task tuning configs (i.e., ignoring the default value or any user configured value). `maxRowsInMemory` will also be overridden to an essentially unlimited value: the Indexer does not support row limits.
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By default, `druid.worker.globalIngestionHeapLimitBytes` is set to 1/6th of the available JVM heap. This default is chosen to align with the default value of `maxBytesInMemory` in task tuning configs when using the MiddleManager/Peon system, which is also 1/6th of the JVM heap.
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The peak usage for rows held in heap memory relates to the interaction between the `maxBytesInMemory` and `maxPendingPersists` properties in the task tuning configs. When the amount of row data held in-heap by a task reaches the limit specified by `maxBytesInMemory`, a task will persist the in-heap row data. After the persist has been started, the task can again ingest up to `maxBytesInMemory` bytes worth of row data while the persist is running.
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This means that the peak in-heap usage for row data can be up to approximately `maxBytesInMemory` * (2 + `maxPendingPersists`). The default value of `maxPendingPersists` is 0, which allows for 1 persist to run concurrently with ingestion work.
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The remaining portion of the heap is reserved for query processing and segment persist/merge operations, and miscellaneous heap usage.
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#### Concurrent segment persist/merge limits
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To help reduce peak memory usage, the Indexer imposes a limit on the number of concurrent segment persist/merge operations across all running tasks.
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By default, the number of concurrent persist/merge operations is limited to (`druid.worker.capacity` / 2), rounded down. This limit can be configured with the `druid.worker.numConcurrentMerges` property.
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### Current limitations
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Separate task logs are not currently supported when using the Indexer; all task log messages will instead be logged in the Indexer process log.
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The Indexer currently imposes an identical memory limit on each task. In later releases, the per-task memory limit will be removed and only the global limit will apply. The limit on concurrent merges will also be removed.
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In later releases, per-task memory usage will be dynamically managed. Please see https://github.com/apache/druid/issues/7900 for details on future enhancements to the Indexer.
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