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:
Short-term share/exclusive page-level locks are used for read/write access. Locks are released immediately after each index tuple is fetched or inserted. B-tree indexes provide the highest concurrency without deadlock conditions.
Share/exclusive index-level locks are used for read/write access. Locks are released after the statement (command) is done.
Share/exclusive page-level locks are used for read/write access. Locks are released after the page is processed. Page-level locks provide better concurrency than index-level ones but are liable to deadlocks.
In short, B-tree indexes are the recommended index type for concurrent applications.
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