3rd October 2019: PostgreSQL 12 Released!
Supported Versions: Current (12) / 11 / 10 / 9.6 / 9.5 / 9.4
Development Versions: devel
Unsupported versions: 9.3 / 9.2 / 9.1 / 9.0 / 8.4 / 8.3 / 8.2 / 8.1 / 8.0 / 7.4 / 7.3 / 7.2
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9.7. Locking and Indexes

Though PostgreSQL provides nonblocking read/write access to table data, nonblocking read/write access is not currently offered for every index access method implemented in PostgreSQL.

The various index types are handled as follows:

GiST and R-Tree indexes

Share/exclusive index-level locks are used for read/write access. Locks are released after statement is done.

Hash indexes

Share/exclusive page-level locks are used for read/write access. Locks are released after page is processed.

Page-level locks provide better concurrency than index-level ones but are subject to deadlocks.

B-tree indexes

Short-term share/exclusive page-level locks are used for read/write access. Locks are released immediately after each index tuple is fetched/inserted.

B-tree indexes provide the highest concurrency without deadlock conditions.

In short, B-tree indexes are the recommended index type for concurrent applications.