Background
Background
When IoTDB service is started, metadata information is organized by loading log file mlog.bin and the results are held
in memory for a long time. As metadata continues to grow, memory continues to grow. In order to support the controllable
fluctuation in the massive metadata scenario, we provide a metadata storage type based on rocksDB.
Usage
Firstly, you should package schema-engine-rocksdb by the following command:
mvn clean package -pl schema-engine-rocksdb -am -DskipTests
After that, you can get a conf directory and a lib directory in
schema-engine-rocksdb/target/schema-engine-rocksdb. Copy the file in the conf directory to the conf directory of server,
and copy the files in the lib directory to the lib directory of server.
Then, open the iotdb-datanode.properties in the conf directory of server, and set the schema_engine_mode to
Rocksdb_based. Restart the IoTDB, the system will use RSchemaRegion to manage the metadata.
####################
### Schema Engine Configuration
####################
# Choose the mode of schema engine. The value could be Memory,Schema_File and Rocksdb_based. If the provided value doesn't match any pre-defined value, Memory mode will be used as default.
# Datatype: string
schema_engine_mode=Rocksdb_based
When rocksdb is specified as the metadata storage type, configuration parameters of rocksDB are open to the public as file. You can modify the configuration file schema-rocksdb.properties to adjust parameters according to your own requirements, such as block cache. If there is no special requirement, use the default value.
Function Support
The module is still being improved, and some functions are not supported at the moment. The function modules are supported as follows:
| function | support |
|---|---|
| timeseries addition and deletion | yes |
| query the wildcard path(* and **) | yes |
| tag addition and deletion | yes |
| aligned timeseries | yes |
| wildcard node name(*) | no |
| meta template | no |
| tag index | no |
| continuous query | no |
Appendix: Interface support
The external interface, that is, the client can sense, related SQL is not supported;
The internal interface, that is, the invocation logic of other modules within the service, has no direct dependence on the external SQL;
| interface | type | support | comment |
|---|---|---|---|
| createTimeseries | external | yes | |
| createAlignedTimeSeries | external | yes | |
| showTimeseries | external | part of the support | not support LATEST |
| changeAlias | external | yes | |
| upsertTagsAndAttributes | external | yes | |
| addAttributes | external | yes | |
| addTags | external | yes | |
| dropTagsOrAttributes | external | yes | |
| setTagsOrAttributesValue | external | yes | |
| renameTagOrAttributeKey | external | yes | |
| *template | external | no | |
| *trigger | external | no | |
| deleteSchemaRegion | internal | yes | |
| autoCreateDeviceMNode | internal | no | |
| isPathExist | internal | yes | |
| getAllTimeseriesCount | internal | yes | |
| getDevicesNum | internal | yes | |
| getNodesCountInGivenLevel | internal | conditional support | path does not support wildcard |
| getMeasurementCountGroupByLevel | internal | yes | |
| getNodesListInGivenLevel | internal | conditional support | path does not support wildcard |
| getChildNodePathInNextLevel | internal | conditional support | path does not support wildcard |
| getChildNodeNameInNextLevel | internal | conditional support | path does not support wildcard |
| getBelongedDevices | internal | yes | |
| getMatchedDevices | internal | yes | |
| getMeasurementPaths | internal | yes | |
| getMeasurementPathsWithAlias | internal | yes | |
| getAllMeasurementByDevicePath | internal | yes | |
| getDeviceNode | internal | yes | |
| getMeasurementMNodes | internal | yes | |
| getSeriesSchemasAndReadLockDevice | internal | yes |