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0 44.8 19.2 44.8 44.8v192z"></path></svg></button></div><div class="toc-wrapper"><ul class="toc-list"><!--[--><li class="toc-item"><a class="vp-link toc-link level2 toc-link level2" href="#basic-concepts-of-iotdb-cluster">Basic Concepts of IoTDB Cluster</a></li><li><ul class="toc-list"><!--[--><li class="toc-item"><a class="vp-link toc-link level3 toc-link level3" href="#concepts">Concepts</a></li><!----><!--]--></ul></li><!--]--><!--[--><li class="toc-item"><a class="vp-link toc-link level2 toc-link level2" href="#characteristics-of-cluster">Characteristics of Cluster</a></li><!----><!--]--><!--[--><li class="toc-item"><a class="vp-link toc-link level2 toc-link level2" href="#partitioning-strategy">Partitioning Strategy</a></li><!----><!--]--><!--[--><li class="toc-item"><a class="vp-link toc-link level2 toc-link level2" href="#replication-strategy">Replication Strategy</a></li><!----><!--]--><!--[--><li class="toc-item"><a class="vp-link toc-link level2 toc-link level2" 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--><h1 id="cluster-concept" tabindex="-1"><a class="header-anchor" href="#cluster-concept" aria-hidden="true">#</a> Cluster Concept</h1><h2 id="basic-concepts-of-iotdb-cluster" tabindex="-1"><a class="header-anchor" href="#basic-concepts-of-iotdb-cluster" aria-hidden="true">#</a> Basic Concepts of IoTDB Cluster</h2><p>Apache IoTDB Cluster contains two types of nodes: ConfigNode and DataNode, each is a process that could be deployed independently.</p><p>An illustration of the cluster architecture：</p><img style="width:100%;max-width:500px;max-height:400px;margin-left:auto;margin-right:auto;display:block;" src="https://alioss.timecho.com/docs/img/UserGuide/Cluster/Architecture.png?raw=true"><p>ConfigNode is the control node of the cluster, which manages the cluster&#39;s node status, partition information, etc. All ConfigNodes in the cluster form a highly available group, which is fully replicated.</p><p>Notice：The replication factor of ConfigNode is all ConfigNodes that has joined the Cluster. Over half of the ConfigNodes is Running could the cluster work.</p><p>DataNode stores the data and schema of the cluster, which manages multiple data regions and schema regions. Data is a time-value pair, and schema is the path and data type of each time series.</p><p>Client could only connect to the DataNode for operation.</p><h3 id="concepts" tabindex="-1"><a class="header-anchor" href="#concepts" aria-hidden="true">#</a> Concepts</h3><table><thead><tr><th style="text-align:left;">Concept</th><th style="text-align:left;">Type</th><th style="text-align:left;">Description</th></tr></thead><tbody><tr><td style="text-align:left;">ConfigNode</td><td style="text-align:left;">node role</td><td style="text-align:left;">Configuration node, which manages cluster node information and partition information, monitors cluster status and controls load balancing</td></tr><tr><td style="text-align:left;">DataNode</td><td style="text-align:left;">node role</td><td style="text-align:left;">Data node, which manages data and meta data</td></tr><tr><td style="text-align:left;">Database</td><td style="text-align:left;">meta data</td><td style="text-align:left;">Database, data are isolated physically from different databases</td></tr><tr><td style="text-align:left;">DeviceId</td><td style="text-align:left;">device id</td><td style="text-align:left;">The full path from root to the penultimate level in the metadata tree represents a device id</td></tr><tr><td style="text-align:left;">SeriesSlot</td><td style="text-align:left;">schema partition</td><td style="text-align:left;">Each database contains many SeriesSlots, the partition key being DeviceId</td></tr><tr><td style="text-align:left;">SchemaRegion</td><td style="text-align:left;">schema region</td><td style="text-align:left;">A collection of multiple SeriesSlots</td></tr><tr><td style="text-align:left;">SchemaRegionGroup</td><td style="text-align:left;">logical concept</td><td style="text-align:left;">The number of SchemaRegions contained in group is the number of schema replicas, it manages the same schema data, and back up each other</td></tr><tr><td style="text-align:left;">SeriesTimeSlot</td><td style="text-align:left;">data partition</td><td style="text-align:left;">The data of a time interval of SeriesSlot, a SeriesSlot contains multiple SeriesTimeSlots, the partition key being timestamp</td></tr><tr><td style="text-align:left;">DataRegion</td><td style="text-align:left;">data region</td><td style="text-align:left;">A collection of multiple SeriesTimeSlots</td></tr><tr><td style="text-align:left;">DataRegionGroup</td><td style="text-align:left;">logical concept</td><td style="text-align:left;">The number of DataRegions contained in group is the number of data replicas, it manages the same data, and back up each other</td></tr></tbody></table><h2 id="characteristics-of-cluster" tabindex="-1"><a class="header-anchor" href="#characteristics-of-cluster" aria-hidden="true">#</a> Characteristics of Cluster</h2><ul><li>Native Cluster Architecture <ul><li>All modules are designed for cluster.</li><li>Standalone is a special form of Cluster.</li></ul></li><li>High Scalability <ul><li>Support adding nodes in a few seconds without data migration.</li></ul></li><li>Massive Parallel Processing Architecture <ul><li>Adopt the MPP architecture and volcano module for data processing, which have high extensibility.</li></ul></li><li>Configurable Consensus Protocol <ul><li>We could adopt different consensus protocol for data replicas and schema replicas.</li></ul></li><li>Extensible Partition Strategy <ul><li>The cluster adopts the lookup table for data and schema partitions, which is flexible to extend.</li></ul></li><li>Built-in Metric Framework <ul><li>Monitor the status of each node in cluster.</li></ul></li></ul><h2 id="partitioning-strategy" tabindex="-1"><a class="header-anchor" href="#partitioning-strategy" aria-hidden="true">#</a> Partitioning Strategy</h2><p>The partitioning strategy partitions data and schema into different Regions, and allocates Regions to different DataNodes.</p><p>It is recommended to set 1 database, and the cluster will dynamically allocate resources according to the number of nodes and cores.</p><p>The database contains multiple SchemaRegions and DataRegions, which are managed by DataNodes.</p><ul><li>Schema partition strategy <ul><li>For a time series schema, the ConfigNode maps the device ID (full path from root to the penultimate tier node) into a SeriesSlot and allocate this SeriesSlot to a SchemaRegionGroup.</li></ul></li><li>Data partition strategy <ul><li>For a time series data point, the ConfigNode will map to a SeriesSlot according to the DeviceId, and then map it to a SeriesTimeSlot according to the timestamp, and allocate this SeriesTimeSlot to a DataRegionGroup.</li></ul></li></ul><p>IoTDB uses a slot-based partitioning strategy, so the size of the partition information is controllable and does not grow infinitely with the number of time series or devices.</p><p>Regions will be allocated to different DataNodes to avoid single point of failure, and the load balance of different DataNodes will be ensured when Regions are allocated.</p><h2 id="replication-strategy" tabindex="-1"><a class="header-anchor" href="#replication-strategy" aria-hidden="true">#</a> Replication Strategy</h2><p>The replication strategy replicates data in multiple replicas, which are copies of each other. Multiple copies can provide high-availability services together and tolerate the failure of some copies.</p><p>A region is the basic unit of replication. Multiple replicas of a region construct a high-availability RegionGroup.</p><ul><li>Replication and consensus <ul><li>ConfigNode Group: Consisting of all ConfigNodes.</li><li>SchemaRegionGroup: The cluster has multiple SchemaRegionGroups, and each SchemaRegionGroup has multiple SchemaRegions with the same id.</li><li>DataRegionGroup: The cluster has multiple DataRegionGroups, and each DataRegionGroup has multiple DataRegions with the same id.</li></ul></li></ul><p>An illustration of the partition allocation in cluster:</p><img style="width:100%;max-width:500px;max-height:500px;margin-left:auto;margin-right:auto;display:block;" src="https://alioss.timecho.com/docs/img/UserGuide/Cluster/Data-Partition.png?raw=true"><p>The figure contains 1 SchemaRegionGroup, and the schema_replication_factor is 3, so the 3 white SchemaRegion-0s form a replication group.</p><p>The figure contains 3 DataRegionGroups, and the data_replication_factor is 3, so there are 9 DataRegions in total.</p><h2 id="consensus-protocol-consistency-protocol" tabindex="-1"><a class="header-anchor" href="#consensus-protocol-consistency-protocol" aria-hidden="true">#</a> Consensus Protocol (Consistency Protocol)</h2><p>Among multiple Regions of each RegionGroup, consistency is guaranteed through a consensus protocol, which routes read and write requests to multiple replicas.</p><ul><li>Current supported consensus protocol <ul><li>SimpleConsensus：Provide strong consistency, could only be used when replica is 1, which is the empty implementation of the consensus protocol.</li><li>IoTConsensus：Provide eventual consistency, could be used in any number of replicas, 2 replicas could avoid single point failure, only for DataRegion, writings can be applied on each replica and replicated asynchronously to other replicas.</li><li>RatisConsensus：Provide Strong consistency, using raft consensus protocol, Could be used in any number of replicas, and could be used for any region groups.<br> Currently, DataRegion uses RatisConsensus does not support multiple data directories. 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