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CACHE TABLE |
CACHE TABLE |
Licensed to the Apache Software Foundation (ASF) under one or more
contributor license agreements. See the NOTICE file distributed with
this work for additional information regarding copyright ownership.
The ASF licenses this file to You under the Apache License, Version 2.0
(the "License"); you may not use this file except in compliance with
the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
|
CACHE TABLE
statement caches contents of a table or output of a query with the given storage level. This reduces scanning of the original files in future queries.
{% highlight sql %} CACHE [ LAZY ] TABLE table_name [ OPTIONS ( 'storageLevel' [ = ] value ) ] [ [ AS ] query ] {% endhighlight %}
LAZY
- Only cache the table when it is first used, instead of immediately.
table_name
- The name of the table to be cached.
OPTIONS ( 'storageLevel' [ = ] value )
-
OPTIONS
clause withstorageLevel
key and value pair. A Warning is issued when a key other thanstorageLevel
is used. The valid options forstorageLevel
are:NONE
DISK_ONLY
DISK_ONLY_2
MEMORY_ONLY
MEMORY_ONLY_2
MEMORY_ONLY_SER
MEMORY_ONLY_SER_2
MEMORY_AND_DISK
MEMORY_AND_DISK_2
MEMORY_AND_DISK_SER
MEMORY_AND_DISK_SER_2
OFF_HEAP
storageLevel
. IfstorageLevel
is not explicitly set usingOPTIONS
clause, the defaultstorageLevel
is set toMEMORY_AND_DISK
.
query
- A query that produces the rows to be cached. It can be in one of following formats:
- a
SELECT
statement - a
TABLE
statement - a
FROM
statement
- a
{% highlight sql %} CACHE TABLE testCache OPTIONS ('storageLevel' 'DISK_ONLY') SELECT * FROM testData; {% endhighlight %}