Composite Index using JPA

Question

I am new to JPA and the concept of Indexing.

I have defined composite index using JPA:

 @Table(name = "table_name", indexes = { @Index(name = "my_index", columnList = "id, user_id") })

My question is can I use the index to retrieve data from database using a service.

Index is used by database, you just should create it, nothing more. — J-Alex, Jun 01 '17 at 16:10

J-Alex · Accepted Answer · 2017-06-01T18:39:51.353

1

Lets shortly clarify what's index and why it's used:

Index is used to increase performance of select statements by using binary search on additionally created data structure which stores values and pointer to original record.

Cons:

Slowdowns the create, update, delete queries if you're updating the indexed column, because index is also updated with the data.
Requires additional disk space.

The primary key of the table is always indexed by default.

Therefore, cannot explicitly use indexes, but your database does.

You can find excellend explanation of indexing here

edited Jun 01 '17 at 18:39

answered Jun 01 '17 at 16:28

J-Alex

"Requires additional disk space." as well as RAM? – harshavmb Jun 01 '17 at 16:35
Yes, the data is also cached, and consumes memory, but also uses virtual memory – J-Alex Jun 01 '17 at 16:45

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