Maintenance Command

    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.

    MERGE

    Execute Level Compaction and unsequence Compaction task. Currently IoTDB supports the following two types of SQL to manually trigger the compaction process of data files:

    • Execute the level compaction first and then execute the unsequence compaction. In unsequence compaction process, this command is executed very fast by rewriting the overlapped Chunks only, while there is some redundant data on the disk eventually.
    • FULL MERGE Execute the level compaction first and then execute the unsequence compaction. In unsequence compaction process, this command is executed slow due to it takes more time to rewrite all data in overlapped files. However, there won’t be any redundant data on the disk eventually.
    1. IoTDB> FULL MERGE

    Clear the cache of chunk, chunk metadata and timeseries metadata to release the memory footprint.

    SET STSTEM TO READONLY / WRITABLE

    Manually set IoTDB system to read-only or writable mode.

    1. IoTDB> SET SYSTEM TO READONLY

    Timeout

    IoTDB supports session and query level 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 session_timeout_threshold parameter in IoTDB configuration file.

    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.

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

    In addition to waiting for the query to time out passively, IoTDB also supports stopping the query actively:

      You can abort the specified query by specifying queryId. If queryId is not specified, all executing queries will be killed.

      The maximum display length of statement is 64 characters. For statements with more than 64 characters, the intercepted part will be displayed.