Hey Xuelin, which data item in the Web UI did you check?
On 1/7/15 5:37 PM, Xuelin Cao wrote:
Hi,
Curious and curious. I'm puzzled by the Spark SQL cached table.
Theoretically, the cached table should be columnar table, and only
scan the column that included in my SQL.
However, in my test, I always see the whole table is scanned even
though I only "select" one column in my SQL.
Here is my code:
/val sqlContext = new org.apache.spark.sql.SQLContext(sc)
/
/import sqlContext._
/
/sqlContext.jsonFile("/data/ad.json").registerTempTable("adTable")
/
/sqlContext.cacheTable("adTable") //The table has > 10 columns/
/
/
///First run, cache the table into memory//
/
/sqlContext.sql("select * from adTable").collect/
/
/
///Second run, only one column is used. It should only scan a small
fraction of data//
/
/sqlContext.sql("select adId from adTable").collect /
/sqlContext.sql("select adId from adTable").collect
/
/sqlContext.sql("select adId from adTable").collect/
What I found is, every time I run the SQL, in WEB UI, it shows
the total amount of input data is always the same --- the total amount
of the table.
Is anything wrong? My expectation is:
1. The cached table is stored as columnar table
2. Since I only need one column in my SQL, the total amount of
input data showed in WEB UI should be very small
But what I found is totally not the case. Why?
Thanks
