Prosvjed invalidating, in·val·i·date
If you specify a table name, only the metadata for that one table is flushed. Therefore, if some other entity modifies information used by Impala in the metastore that Thaidarling dating and Hive share, the information cached by Impala must be updated.
Kudu tables have less reliance on the metastore database, and require less metadata caching on the Impala side. For a huge table, that process could take a noticeable amount of time; thus you might prefer to use REFRESH where practical, to avoid an unpredictable delay later, for example if the next reference to the table is during a benchmark test.
However, this does not mean that all metadata updates require an Impala update. Neither statement is needed when data is added to, removed, or updated in a Kudu table, even if the changes are made directly to Kudu through a client program using the Kudu API.
If you used Impala version 1. A table could have data spread across multiple directories, or in unexpected paths, if it uses partitioning or specifies a LOCATION attribute for individual partitions or the entire table.
See New Features in Impala 1.
The user ID that the impalad daemon runs under, typically the impala user, must have execute permissions for all the relevant directories holding table data. Database and table metadata is typically modified by: Much of the metadata for Kudu tables is handled by the underlying storage layer.
Impala reports any lack of write permissions as an INFO message in the log file, in case that represents an oversight. Now, newly created or altered objects are picked up automatically by all Impala nodes.
For example, information about partitions in Kudu tables is managed by Kudu, and Impala does not cache any block locality metadata for Kudu tables. To accurately respond to queries, Impala must have current metadata about those databases and tables that clients query directly.
Required after a table is created through the Hive shell, before the table is available for Impala queries.
REFRESH reloads the metadata immediately, but only loads the block location data for newly added data files, making it a less expensive operation overall. See The Impala Catalog Service for more information on the catalog service.
The next time the current Impala node performs a query against a table whose metadata is invalidated, Impala reloads the associated metadata before the query proceeds.