Cache And Uncache Tables

Description

Spark SQL can cache tables using an in-memory columnar format by calling cache_table(). Spark SQL will scan only required columns and will automatically tune compression to minimize memory usage and GC pressure. You can call uncache_table() to remove the table from memory. Similarly you can call clear_cache() to remove all cached tables from the in-memory cache. Finally, use is_cached() to test whether or not a table is cached.

Usage

cache_table(sc, table)

clear_cache(sc)

is_cached(sc, table)

uncache_table(sc, table)

Arguments

Value

• cache_table(): If successful, TRUE, otherwise FALSE.

• clear_cache(): NULL, invisibly.

• is_cached(): A logical(1) vector indicating TRUE if the table is cached and FALSE otherwise.

• uncache_table(): NULL, invisibly.

See Also

create_table(), get_table(), list_tables(), refresh_table(), table_exists(), uncache_table()

Examples

## Not run: 
sc <- sparklyr::spark_connect(master = "local")
mtcars_spark <- sparklyr::copy_to(dest = sc, df = mtcars)

# By default the table is not cached
is_cached(sc = sc, table = "mtcars")

# We can manually cache the table
cache_table(sc = sc, table = "mtcars")
# And now the table is cached
is_cached(sc = sc, table = "mtcars")

# We can uncache the table
uncache_table(sc = sc, table = "mtcars")
is_cached(sc = sc, table = "mtcars")

## End(Not run)

Create A Table

Description

Creates a table, in the hive warehouse, from the given path and returns the corresponding DataFrame. The table will contain the contents of the file that is in the path parameter.

Usage

create_table(sc, table, path, source, ...)

Arguments

Details

The default data source type is parquet. This can be changed using source or setting the configuration option spark.sql.sources.default when creating the spark session using or after you have created the session using

config <- sparklyr::spark_config()
config[["spark.sql.sources.default"]] <- "csv"

Value

A tbl_spark.

See Also

cache_table(), get_table(), list_tables(), refresh_table(), table_exists(), uncache_table()

Get The Current Database

Description

Returns the current database in this session. By default your session will be connected to the "default" database (named "default") and to change database you can use set_current_database().

Usage

current_database(sc)

Arguments

Value

character(1), the current database name.

See Also

set_current_database(), database_exists(), list_databases()

Examples

## Not run: 
sc <- sparklyr::spark_connect(master = "local")
current_database(sc = sc)

## End(Not run)

Check If A Database Exists

Description

Check if the database with the specified name exists. This will check the list of hive databases in the current session to see if the database exists.

Usage

database_exists(sc, name)

Arguments

Value

A logical(1) vector indicating TRUE if the database exists and FALSE otherwise.

See Also

current_database(), set_current_database(), list_databases()

Examples

## Not run: 
sc <- sparklyr::spark_connect(master = "local")
database_exists(sc = sc, name = "default")
database_exists(sc = sc, name = "fake_database")

## End(Not run)

Temporary View

Description

• drop_global_temp_view(): Drops the global temporary view with the given view name in the catalog.

• drop_temp_view(): Drops the local temporary view with the given view name in the catalog. Local temporary view is session-scoped. Its lifetime is the lifetime of the session that created it, i.e. it will be automatically dropped when the session terminates. It's not tied to any databases.

Usage

drop_global_temp_view(sc, view)

drop_temp_view(sc, view)

Arguments

Value

A logical(1) vector indicating whether the temporary view was dropped (TRUE) or not (FALSE).

See Also

list_tables()

Examples

## Not run: 
sc <- sparklyr::spark_connect(master = "local")
mtcars_spark <- sparklyr::copy_to(dest = sc, df = mtcars)

# We can check which temporary tables are in scope
list_tables(sc = sc)

# And then drop those we wish to drop
drop_temp_view(sc = sc, view = "mtcars")

## End(Not run)

Check If A Function Exists

Description

Check if the function with the specified name exists in the specified database.

Usage

function_exists(sc, fn, database = NULL)

Arguments

Details

function_exists() includes in-built functions such as abs. To see if a built-in function exists you must use the unqualified name. If you create a function you can use the qualified name. If you want to check if a built-in function exists specify the database as NULL.

Value

A logical(1) vector indicating TRUE if the function exists within the specified database and FALSE otherwise.

Examples

## Not run: 
sc <- sparklyr::spark_connect(master = "local")
function_exists(sc = sc, fn = "abs")

## End(Not run)

Get A Function

Description

Get the function with the specified name.

Usage

get_function(sc, fn, database = NULL)

Arguments

Details

If you are trying to get an in-built function then use the unqualified name and pass NULL as the database name.

Value

A spark_jobj which includes the class name, database, description, whether it is temporary and the name of the function.

See Also

function_exists(), list_functions()

Examples

## Not run: 
sc <- sparklyr::spark_connect(master = "local")
get_function(sc = sc, fn = "Not")

## End(Not run)

Get A Table

Description

Get the table or view with the specified name in the specified database. You can use this to find the table's description, database, type and whether it is a temporary table or not.

Usage

get_table(sc, table, database = NULL)

Arguments

Value

An object of class spark_jobj and shell_jobj.

See Also

cache_table(), create_table(), list_tables(), refresh_table(), table_exists(), uncache_table()

List Columns

Description

Returns a list of columns for the given table/view in the specified database. The result includes the name, description, dataType, whether it is nullable or if it is partitioned and if it is broken in buckets.

Usage

list_columns(sc, table, database = NULL)

Arguments

Value

A tibble with 6 columns:

• name - The name of the column.

• description - Description of the column.

• dataType - The column data type.

• nullable - Whether the column is nullable or not.

• isPartition - Whether the column is partitioned or not.

• isBucket - Whether the column is broken in buckets.

Examples

## Not run: 
sc <- sparklyr::spark_connect(master = "local")
mtcars_spark <- sparklyr::copy_to(dest = sc, df = mtcars)
list_columns(sc = sc, table = "mtcars")

## End(Not run)

List Databases

Description

Returns a list of databases available across all sessions. The result contains the name, description and locationUri of each database.

Usage

list_databases(sc)

Arguments

Value

A tibble containing 3 columns:

• name - The name of the database.

• description - Description of the database.

• locationUri - Path (in the form of a uri) to data files.

See Also

current_database(), database_exists(), set_current_database()

Examples

## Not run: 
sc <- sparklyr::spark_connect(master = "local")
list_databases(sc = sc)

## End(Not run)

List Functions

Description

Returns a list of functions registered in the specified database. This includes all temporary functions. The result contains the class name, database, description, whether it is temporary and the name of each function.

Usage

list_functions(sc, database = NULL)

Arguments

Value

A tibble containing 5 columns:

• name - Name of the function.

• database - Name of the database the function belongs to.

• description - Description of the function.

• className - The fully qualified class name of the function.

• isTemporary - Whether the function is temporary or not.

See Also

function_exists(), get_function()

Examples

## Not run: 
sc <- sparklyr::spark_connect(master = "local")
list_functions(sc = sc)
list_functions(sc = sc, database = "default")

## End(Not run)

List Tables In A Spark Connection

Description

Returns a list of tables/views in the current database. The result includes the name, database, description, table type and whether the table is temporary or not.

Usage

list_tables(sc, database = NULL)

Arguments

Value

A tibble containing 5 columns:

• name - The name of the table.

• database - Name of the database the table belongs to.

• description - Description of the table.

• tableType - The type of table (e.g. view/table)

• isTemporary - Whether the table is temporary or not.

See Also

cache_table(), create_table(), get_table(), refresh_table(), table_exists(), uncache_table()

Examples

## Not run: 
sc <- sparklyr::spark_connect(master = "local")
mtcars_spakr <- sparklyr::copy_to(dest = sc, df = mtcars)
list_tables(sc = sc)

## End(Not run)

Refreshing Data

Description

• recover_partitions(): Recovers all the partitions in the directory of a table and update the catalog. This only works for partitioned tables and not un-partitioned tables or views.

• refresh_by_path(): Invalidates and refreshes all the cached data (and the associated metadata) for any Dataset that contains the given data source path. Path matching is by prefix, i.e. "/" would invalidate everything that is cached.

• refresh_table(): Invalidates and refreshes all the cached data and metadata of the given table. For performance reasons, Spark SQL or the external data source library it uses might cache certain metadata about a table, such as the location of blocks. When those change outside of Spark SQL, users should call this function to invalidate the cache. If this table is cached as an InMemoryRelation, drop the original cached version and make the new version cached lazily.

Usage

recover_partitions(sc, table)

refresh_by_path(sc, path)

refresh_table(sc, table)

Arguments

Value

NULL, invisibly. These functions are mostly called for their side effects.

See Also

cache_table(), create_table(), get_table(), list_tables(), table_exists(), uncache_table()

Set The Current Database

Description

Sets the current default database in this session.

Usage

set_current_database(sc, name)

Arguments

Value

If successful, TRUE, otherwise errors.

See Also

current_database(), database_exists(), list_databases()

Examples

## Not run: 
sc <- sparklyr::spark_connect(master = "local")
set_current_database(sc = sc, name = "new_db")

## End(Not run)

Check If A Table Exists

Description

Check if the table or view with the specified name exists in the specified database. This can either be a temporary view or a table/view.

Usage

table_exists(sc, table, database = NULL)

Arguments

Details

If database is NULL, table_exists refers to a table in the current database (see current_database()).

Value

A logical(1) vector indicating TRUE if the table exists within the specified database and FALSE otherwise.

See Also

cache_table(), create_table(), get_table(), list_tables(), refresh_table(), uncache_table()

Examples

## Not run: 
sc <- sparklyr::spark_connect(master = "local")
mtcars_spark <- sparklyr::copy_to(dest = sc, df = mtcars)
table_exists(sc = sc, table = "mtcars")

## End(Not run)