being disabled and dating - Invalidating stale

Because this operation adds a delay to the next query against each table, potentially expensive for large tables with many partitions, try to avoid using this option for day-to-day operations in a production environment.

invalidating stale-61invalidating stale-11invalidating stale-20

Therefore, if some other entity modifies information used by Impala in the metastore that Impala and Hive share, the information cached by Impala must be updated.

However, this does not mean that all metadata updates require an Impala update.

This tells the Item class how it should handle a miss, and what it should do while another class is processing data.

The example below tells the Item class that it should switch from the default method of precomputing a value before it expires and that it should instead wait until the expiration and continue using stale values while another process regenerates the data.

These features are all ways to deal with stale data in such a way that only one request has to regenerate it.

The default method is by triggering a single cache miss in advance so that a single process will regenerate the data before the data actually expires.

Required after a table is created through the Hive shell, before the table is available for Impala queries.

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.

Unfortunately by this point the system load will also have risen considerably, making that five second processing time rise to higher and higher numbers.

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