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Dongjoon Hyun b421bf0196 [SPARK-32517][CORE] Add StorageLevel.DISK_ONLY_3 
### What changes were proposed in this pull request?

This PR aims to add `StorageLevel.DISK_ONLY_3` as a built-in `StorageLevel`.

### Why are the changes needed?

In a YARN cluster, HDFS uaually provides storages with replication factor 3. So, we can save the result to HDFS to get `StorageLevel.DISK_ONLY_3` technically. However, disaggregate clusters or clusters without storage services are rising. Previously, in that situation, the users were able to use similar `MEMORY_AND_DISK_2` or a user-created `StorageLevel`. This PR aims to support those use cases officially for better UX.

### Does this PR introduce _any_ user-facing change?

Yes. This provides a new built-in option.

### How was this patch tested?

Pass the GitHub Action or Jenkins with the revised test cases.

Closes #29331 from dongjoon-hyun/SPARK-32517.

Authored-by: Dongjoon Hyun <dongjoon@apache.org>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>
2020-08-10 07:33:06 -07:00

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global 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.

Description

CACHE TABLE statement caches contents of a table or output of a query with the given storage level. If a query is cached, then a temp view will be created for this query. This reduces scanning of the original files in future queries.

Syntax

CACHE [ LAZY ] TABLE table_identifier
    [ OPTIONS ( 'storageLevel' [ = ] value ) ] [ [ AS ] query ]

Parameters

  • LAZY

    Only cache the table when it is first used, instead of immediately.

  • table_identifier

    Specifies the table or view name to be cached. The table or view name may be optionally qualified with a database name.

    Syntax: [ database_name. ] table_name

  • OPTIONS ( 'storageLevel' [ = ] value )

    OPTIONS clause with storageLevel key and value pair. A Warning is issued when a key other than storageLevel is used. The valid options for storageLevel are:

    • NONE
    • DISK_ONLY
    • DISK_ONLY_2
    • DISK_ONLY_3
    • 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

    An Exception is thrown when an invalid value is set for storageLevel. If storageLevel is not explicitly set using OPTIONS clause, the default storageLevel is set to MEMORY_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

Examples

CACHE TABLE testCache OPTIONS ('storageLevel' 'DISK_ONLY') SELECT * FROM testData;

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