CacheTableCommand Runnable Logical Command¶

When <>, CacheTableCommand creates a DataFrame followed by registering a temporary view for the optional query.

CACHE LAZY? TABLE [table] (AS? [query])?

CacheTableCommand requests the session-specific Catalog to cache the table.

Note

CacheTableCommand uses SparkSession to access the Catalog.

If the caching is not LAZY (which is not by default), CacheTableCommand creates a DataFrame for the table and counts the rows (that will trigger the caching).

Note

CacheTableCommand uses a Spark SQL pattern to trigger DataFrame caching by executing count operation.

val q = "CACHE TABLE ids AS SELECT * from range(5)"
scala> println(sql(q).queryExecution.logical.numberedTreeString)
00 CacheTableCommand `ids`, false
01    +- 'Project [*]
02       +- 'UnresolvedTableValuedFunction range, [5]

// ids table is already cached but let's use it anyway (and see what happens)
val q2 = "CACHE LAZY TABLE ids"
scala> println(sql(q2).queryExecution.logical.numberedTreeString)
17/05/17 06:16:39 WARN CacheManager: Asked to cache already cached data.
00 CacheTableCommand `ids`, true