In HDFS, the data is stored in blocks. But scanning which data is stored in which block is time consuming. Compact indexing stores the indexed column's value and its blockId. So the query will not go to the table. Instead, the query will directly go to the compact index, where the column value and blockId are stored. No need to scan all the blocks to find data! So, while performing a query, it will first check the index and then go directly into that block.
Compact index
Get Modern Big Data Processing with Hadoop now with the O’Reilly learning platform.
O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.
