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spark-instrumented-optimizer/docs/sql-ref-syntax-aux-cache-cache-table.md
ulysses 184074de22 [SPARK-31999][SQL] Add REFRESH FUNCTION command 
### What changes were proposed in this pull request?

In Hive mode, permanent functions are shared with Hive metastore so that functions may be modified by other Hive client. With in long-lived spark scene, it's hard to update the change of function.

Here are 2 reasons:
* Spark cache the function in memory using `FunctionRegistry`.
* User may not know the location or classname of udf when using `replace function`.

Note that we use v2 command code path to add new command.

### Why are the changes needed?

Give a easy way to make spark function registry sync with Hive metastore.
Then we can call
```
refresh function functionName
```

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

Yes, new command.

### How was this patch tested?

New UT.

Closes #28840 from ulysses-you/SPARK-31999.

Authored-by: ulysses <youxiduo@weidian.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>
2020-07-22 19:05:50 +00:00

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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
    • 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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