Managing Metadata in Impala

This section describes various knobs you can use to control how Impala manages its metadata in order to improve performance and scalability.

On-demand Metadata
With the on-demand metadata feature, the Impala coordinators pull metadata as needed from catalogd and cache it locally. The cached metadata gets evicted automatically under memory pressure.
Automatic Invalidation of Metadata Cache
To keep the size of metadata bounded, the Impala Catalog Server periodically scans all the tables and invalidates those not recently used.
Automatic Invalidation/Refresh of Metadata
In this release, you can invalidate or refresh metadata automatically after changes to databases, tables or partitions render metadata stale. You control the synching of tables or database metadata by basing the process on events. You learn how to access metrics and state information about the invalidate event processor.