How to use index?

1. Create index

The first step for utilizing index is index creation. You can create index using SQL (Data Definition Language) or Tajo API (Tajo Client API). For example, you can create a BST index on the lineitem table by submitting the following SQL to Tajo.

default> create index l_orderkey_idx on lineitem (l_orderkey);

If the index is created successfully, you can see the information about that index as follows:

default> \d lineitem

table name: default.lineitem
table path: hdfs://localhost:7020/tpch/lineitem
store type: CSV
number of rows: unknown
volume: 753.9 MB

l_orderkey    INT8
l_partkey     INT8
l_suppkey     INT8
l_linenumber  INT8
l_quantity    FLOAT4
l_extendedprice       FLOAT4
l_discount    FLOAT4
l_tax FLOAT4
l_returnflag  TEXT
l_linestatus  TEXT
l_shipdate    DATE
l_commitdate  DATE
l_receiptdate DATE
l_shipinstruct        TEXT
l_shipmode    TEXT
l_comment     TEXT

"l_orderkey_idx" TWO_LEVEL_BIN_TREE (l_orderkey ASC NULLS LAST )

For more information about index creation, please refer to the above links.

2. Enable/disable index scans

When an index is successfully created, you must enable the index scan feature as follows:

default> \set INDEX_ENABLED true

If you don’t want to use the index scan feature anymore, you can simply disable it as follows:

default> \set INDEX_ENABLED false


Once the index scan feature is enabled, Tajo currently always performs the index scan regardless of its efficiency. You should set this option when the expected number of retrieved tuples is sufficiently small.