In this recipe, we will be discussing how to create an online index that will not block the base table for the incoming transactions.
In general, while creating/dropping an index, it will block the table to avoid further write operations into the index. Until the index operation is complete, the whole table will be locked for write operations, which will be an outage to the application. To avoid this table lock problem, PostgreSQL provides an option called concurrent, which will avoid this blocking behavior. It will also keep this index status as invalid until its creation is successfully completed. Building an index concurrently takes more time, as the operation needs to allow the incoming write operations.