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Getting started

  • Introduction to Apache Druid
  • Quickstart (local)
  • Single server deployment
  • Clustered deployment

Tutorials

  • Load files natively
  • Load files using SQL ๐Ÿ†•
  • Load from Apache Kafka
  • Load from Apache Hadoop
  • Querying data
  • Roll-up
  • Theta sketches
  • Configuring data retention
  • Updating existing data
  • Compacting segments
  • Deleting data
  • Writing an ingestion spec
  • Transforming input data
  • Tutorial: Run with Docker
  • Kerberized HDFS deep storage
  • Convert ingestion spec to SQL
  • Jupyter Notebook tutorials

Design

  • Design
  • Segments
  • Processes and servers
  • Deep storage
  • Metadata storage
  • ZooKeeper

Ingestion

  • Ingestion
  • Data formats
  • Data model
  • Data rollup
  • Partitioning
  • Ingestion spec
  • Schema design tips
  • Stream ingestion

    • Apache Kafka ingestion
    • Apache Kafka supervisor
    • Apache Kafka operations
    • Amazon Kinesis

    Batch ingestion

    • Native batch
    • Native batch: input sources
    • Migrate from firehose
    • Hadoop-based

    SQL-based ingestion ๐Ÿ†•

    • Overview
    • Key concepts
    • API
    • Security
    • Examples
    • Reference
    • Known issues
  • Task reference
  • Troubleshooting FAQ

Data management

  • Overview
  • Data updates
  • Data deletion
  • Schema changes
  • Compaction
  • Automatic compaction

Querying

    Druid SQL

    • Overview and syntax
    • SQL data types
    • Operators
    • Scalar functions
    • Aggregation functions
    • Multi-value string functions
    • JSON functions
    • All functions
    • Druid SQL API
    • JDBC driver API
    • SQL query context
    • SQL metadata tables
    • SQL query translation
  • Native queries
  • Query execution
  • Troubleshooting
  • Concepts

    • Datasources
    • Joins
    • Lookups
    • Multi-value dimensions
    • Nested columns
    • Multitenancy
    • Query caching
    • Using query caching
    • Query context

    Native query types

    • Timeseries
    • TopN
    • GroupBy
    • Scan
    • Search
    • TimeBoundary
    • SegmentMetadata
    • DatasourceMetadata

    Native query components

    • Filters
    • Granularities
    • Dimensions
    • Aggregations
    • Post-aggregations
    • Expressions
    • Having filters (groupBy)
    • Sorting and limiting (groupBy)
    • Sorting (topN)
    • String comparators
    • Virtual columns
    • Spatial filters

Configuration

  • Configuration reference
  • Extensions
  • Logging

Operations

  • Web console
  • Java runtime
  • Security

    • Security overview
    • User authentication and authorization
    • LDAP auth
    • Password providers
    • Dynamic Config Providers
    • TLS support

    Performance tuning

    • Basic cluster tuning
    • Segment size optimization
    • Mixed workloads
    • HTTP compression
    • Automated metadata cleanup

    Monitoring

    • Request logging
    • Metrics
    • Alerts
  • API reference
  • High availability
  • Rolling updates
  • Using rules to drop and retain data
  • Working with different versions of Apache Hadoop
  • Misc

    • dump-segment tool
    • reset-cluster tool
    • insert-segment-to-db tool
    • pull-deps tool
    • Deep storage migration
    • Export Metadata Tool
    • Metadata Migration
    • Content for build.sbt

Development

  • Developing on Druid
  • Creating extensions
  • JavaScript functionality
  • Build from source
  • Versioning
  • Experimental features

Misc

  • Papers

Hidden

  • Apache Druid vs Elasticsearch
  • Apache Druid vs. Key/Value Stores (HBase/Cassandra/OpenTSDB)
  • Apache Druid vs Kudu
  • Apache Druid vs Redshift
  • Apache Druid vs Spark
  • Apache Druid vs SQL-on-Hadoop
  • Authentication and Authorization
  • Broker
  • Coordinator Process
  • Historical Process
  • Indexer Process
  • Indexing Service
  • MiddleManager Process
  • Overlord Process
  • Router Process
  • Peons
  • Approximate Histogram aggregators
  • Apache Avro
  • Microsoft Azure
  • Bloom Filter
  • DataSketches extension
  • DataSketches HLL Sketch module
  • DataSketches Quantiles Sketch module
  • DataSketches Theta Sketch module
  • DataSketches Tuple Sketch module
  • Basic Security
  • Kerberos
  • Cached Lookup Module
  • Apache Ranger Security
  • Google Cloud Storage
  • HDFS
  • Apache Kafka Lookups
  • Globally Cached Lookups
  • MySQL Metadata Store
  • ORC Extension
  • Druid pac4j based Security extension
  • Apache Parquet Extension
  • PostgreSQL Metadata Store
  • Protobuf
  • S3-compatible
  • Simple SSLContext Provider Module
  • Stats aggregator
  • Test Stats Aggregators
  • Druid AWS RDS Module
  • Kubernetes
  • Ambari Metrics Emitter
  • Apache Cassandra
  • Rackspace Cloud Files
  • DistinctCount Aggregator
  • Graphite Emitter
  • InfluxDB Line Protocol Parser
  • InfluxDB Emitter
  • Kafka Emitter
  • Materialized View
  • Moment Sketches for Approximate Quantiles module
  • Moving Average Query
  • OpenTSDB Emitter
  • Druid Redis Cache
  • Microsoft SQLServer
  • StatsD Emitter
  • T-Digest Quantiles Sketch module
  • Thrift
  • Timestamp Min/Max aggregators
  • GCE Extensions
  • Aliyun OSS
  • Prometheus Emitter
  • kubernetes
  • Cardinality/HyperUnique aggregators
  • Select
  • Firehose (deprecated)
  • Native batch (simple)
  • Realtime Process
Edit

Logging

Apache Druid services emit logs that to help you debug. The same services also emit periodic metrics about their state. To disable metric info logs set the following runtime property: -Ddruid.emitter.logging.logLevel=debug.

Druid uses log4j2 for logging. The default configuration file log4j2.xml ships with Druid at the following path: conf/druid/{config}/_common/log4j2.xml.

By default, Druid uses RollingRandomAccessFile for rollover daily, and keeps log files up to 7 days. If that's not suitable in your case, modify the log4j2.xml accordingly.

The following example log4j2.xml is based upon the micro quickstart:

<?xml version="1.0" encoding="UTF-8" ?>
<Configuration status="WARN">
  <Properties>
    <!-- to change log directory, set DRUID_LOG_DIR environment variable to your directory before launching Druid -->
    <Property name="druid.log.path" value="log" />
  </Properties>

  <Appenders>
    <Console name="Console" target="SYSTEM_OUT">
      <PatternLayout pattern="%d{ISO8601} %p [%t] %c - %m%n"/>
    </Console>

    <!-- Rolling Files-->
    <RollingRandomAccessFile name="FileAppender"
                             fileName="${sys:druid.log.path}/${sys:druid.node.type}.log"
                             filePattern="${sys:druid.log.path}/${sys:druid.node.type}.%d{yyyyMMdd}.log">
      <PatternLayout pattern="%d{ISO8601} %p [%t] %c - %m%n"/>
      <Policies>
        <TimeBasedTriggeringPolicy interval="1" modulate="true"/>
      </Policies>
      <DefaultRolloverStrategy>
        <Delete basePath="${sys:druid.log.path}/" maxDepth="1">
          <IfFileName glob="*.log" />
          <IfLastModified age="7d" />
        </Delete>
      </DefaultRolloverStrategy>
    </RollingRandomAccessFile>

  </Appenders>

  <Loggers>
    <Root level="info">
      <AppenderRef ref="FileAppender"/>
    </Root>

    <!-- Set level="debug" to see stack traces for query errors -->
    <Logger name="org.apache.druid.server.QueryResource" level="info" additivity="false">
      <Appender-ref ref="FileAppender"/>
    </Logger>
    <Logger name="org.apache.druid.server.QueryLifecycle" level="info" additivity="false">
      <Appender-ref ref="FileAppender"/>
    </Logger>

    <!-- Set level="debug" or "trace" to see more Coordinator details (segment balancing, load/drop rules, etc) -->
    <Logger name="org.apache.druid.server.coordinator" level="info" additivity="false">
      <Appender-ref ref="FileAppender"/>
    </Logger>

    <!-- Set level="debug" to see low-level details about segments and ingestion -->
    <Logger name="org.apache.druid.segment" level="info" additivity="false">
      <Appender-ref ref="FileAppender"/>
    </Logger>

    <!-- Set level="debug" to see more information about extension initialization -->
    <Logger name="org.apache.druid.initialization" level="info" additivity="false">
      <Appender-ref ref="FileAppender"/>
    </Logger>

    <!-- Quieter logging at startup -->
    <Logger name="org.skife.config" level="warn" additivity="false">
      <Appender-ref ref="FileAppender"/>
    </Logger>
    <Logger name="com.sun.jersey.guice" level="warn" additivity="false">
      <Appender-ref ref="FileAppender"/>
    </Logger>
  </Loggers>
</Configuration>

NOTE: Although Druid shares the log4j configuration file task peon processes, the appenders in this file DO NOT take effect for peon processes. Peons always output logs to standard output. Middle Managers redirect task logs from standard output to long-term storage.

However, log level settings do take effect for these task peon processes. This means you can configure loggers at different logging level for task logs using log4j2.xml.

Log directory

The included log4j2.xml configuration for Druid and ZooKeeper writes logs to the log directory at the root of the distribution.

If you want to change the log directory, set the environment variable DRUID_LOG_DIR to the right directory before you start Druid.

All-in-one start commands

If you use one of the all-in-one start commands, such as bin/start-micro-quickstart, the default configuration for each service has two kinds of log files. Log4j2 writes the main log file and rotates it periodically. For example, log/historical.log.

The secondary log file contains anything that is written by the component directly to standard output or standard error without going through log4j2. For example, log/historical.stdout.log. This consists mainly of messages from the Java runtime itself. This file is not rotated, but it is generally small due to the low volume of messages. If necessary, you can truncate it using the Linux command truncate --size 0 log/historical.stdout.log.

Avoid reflective access warnings in logs

On Java 11, you may see warnings like the following in the logs:

WARNING: An illegal reflective access operation has occurred
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release

To avoid these, add the --add-exports and --add-opens command line parameters described in the documentation section about Java strong encapsulation.

Set the logs to asynchronously write

If your logs are really chatty, you can set them to write asynchronously. The following example shows a log4j2.xml that configures some of the more chatty classes to write asynchronously:

<?xml version="1.0" encoding="UTF-8" ?>
<Configuration status="WARN">
  <Appenders>
    <Console name="Console" target="SYSTEM_OUT">
      <PatternLayout pattern="%d{ISO8601} %p [%t] %c - %m%n"/>
    </Console>
  </Appenders>
  
<Loggers>
    <!-- AsyncLogger instead of Logger -->
    <AsyncLogger name="org.apache.druid.curator.inventory.CuratorInventoryManager" level="debug" additivity="false">
      <AppenderRef ref="Console"/>
    </AsyncLogger>
    <AsyncLogger name="org.apache.druid.client.BatchServerInventoryView" level="debug" additivity="false">
      <AppenderRef ref="Console"/>
    </AsyncLogger>
    <!-- Make extra sure nobody adds logs in a bad way that can hurt performance -->
    <AsyncLogger name="org.apache.druid.client.ServerInventoryView" level="debug" additivity="false">
      <AppenderRef ref="Console"/>
    </AsyncLogger>
    <AsyncLogger name ="org.apache.druid.java.util.http.client.pool.ChannelResourceFactory" level="info" additivity="false">
      <AppenderRef ref="Console"/>
    </AsyncLogger>
    <Root level="info">
      <AppenderRef ref="Console"/>
    </Root>
  </Loggers>
</Configuration>
โ† ExtensionsWeb console โ†’
  • Log directory
  • All-in-one start commands
  • Avoid reflective access warnings in logs
  • Set the logs to asynchronously write

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