Though Postgres provides unblocking read/write access to table data, unblocked read/write access is not provided for every index access methods implemented in Postgres.
The various index types are handled as follows:
Share/exclusive index-level locks are used for read/write access. Locks are released after statement is done.
Share/exclusive page-level locks are used for read/write access. Locks are released after page is processed.
Page-level locks produces better concurrency than index-level ones but are subject to deadlocks.
Short-term share/exclusive page-level latches are used for read/write access. Latches are released immediately after the index tuple is inserted/fetched.
Btree indices provide the highest concurrency without deadlock conditions.
If you see anything in the documentation that is not correct, does not match your experience with the particular feature or requires further clarification, please use this form to report a documentation issue.