Maintenance Command

FLUSH

Persist all the data points in the memory table of the database to the disk, and seal the data file. In cluster mode, we provide commands to persist the specified database cache of local node and persist the specified database cache of the cluster.

Note: This command does not need to be invoked manually by the client. IoTDB has WAL to ensure data security and IoTDB will flush when appropriate. Frequently call flush can result in small data files that degrade query performance.

  1. IoTDB> FLUSH 
  2. IoTDB> FLUSH ON LOCAL
  3. IoTDB> FLUSH ON CLUSTER
  4. IoTDB> FLUSH root.ln
  5. IoTDB> FLUSH root.sg1,root.sg2 ON LOCAL
  6. IoTDB> FLUSH root.sg1,root.sg2 ON CLUSTER

CLEAR CACHE

Clear the cache of chunk, chunk metadata and timeseries metadata to release the memory footprint. In cluster mode, we provide commands to clear local node cache and clear the cluster cache.

  1. IoTDB> CLEAR CACHE
  2. IoTDB> CLEAR CACHE ON LOCAL
  3. IoTDB> CLEAR CACHE ON CLUSTER

SET SYSTEM TO READONLY / RUNNING

Manually set IoTDB system to running, read-only mode. In cluster mode, we provide commands to set the local node status and set the cluster status, valid for the entire cluster by default.

  1. IoTDB> SET SYSTEM TO RUNNING
  2. IoTDB> SET SYSTEM TO READONLY ON LOCAL
  3. IoTDB> SET SYSTEM TO READONLY ON CLUSTER

Kill Query

IoTDB supports setting session connection timeouts and query timeouts, and also allows to stop the executing query manually.

Session timeout

Session timeout controls when idle sessions are closed. An idle session is one that had not initiated any query or non-query operations for a period of time.

Session timeout is disabled by default and can be set using the dn_session_timeout_threshold parameter in IoTDB configuration file.

Query timeout

For queries that take too long to execute, IoTDB will forcibly interrupt the query and throw a timeout exception, as shown in the figure:

  1. IoTDB> select * from root;
  2. Msg: 701 Current query is time out, please check your statement or modify timeout parameter.

The default timeout of a query is 60000 ms，which can be customized in the configuration file through the query_timeout_threshold parameter.

If you use JDBC or Session, we also support setting a timeout for a single query（Unit: ms）：

  1. ((IoTDBStatement) statement).executeQuery(String sql, long timeoutInMS)
  2. session.executeQueryStatement(String sql, long timeout)

If the timeout parameter is not configured or with a negative number, the default timeout time will be used. If value 0 is used, timeout function will be disabled.

Query abort

Not supported yet