6.5 Query Server Restarts and Metadata Persistence

You can refresh the Query Server metadata using Cloudera Manager, Apache Ambari, or a PL/SQL API.

Upon restart:

• All external tables are available, however Query Server does not support tables that store data. If data is inserted into these tables, the tables are truncated upon restart.
• All metadata including tables, views, security profiles, privileges and roles are preserved.

The following key metadata can be saved so that they can be restored after a Query Server restart:

• Table statistics

  Gathering statistics can be an expensive operation. Table Statistics are gathered automatically after each metadata synchronization. Subsequent statistics gathering may be captured using the following PL/SQL package procedure and parameters:

  DBMS_BDSQS.GATHER_EXTERNAL_TABLE_STATS(
    tabname => <table-name>,
    estimate_percent => dbms_stats.auto_sample_size);

  Note:

  Stats gathered using dbms_bdsqs.gather_external_table_stats will persist a restart. See the DBMS_BDSQS PL/SQL Package.
• All external tables and views.