PG-Locks

表级锁

	ACCESS SHARE	ROW SHARE	ROW EXCLUSIVE	SHARE UPDATE EXCLUSIVE	SHARE	SHARE ROW EXCLUSIVE	EXCLUSIVE	ACCESS EXCLUSIVE	持锁语句	描述
ACCESS SHARE								×	SELECT
ROW SHARE							×	×	SELECT FOR UPDATE SELECT FOR SHARE
ROW EXCLUSIVE					×	×	×	×	INSERT/UPDATE/DELETE
SHARE UPDATE EXCLUSIVE				×	×	×	×	×	CREATE INDEX CURRENTLY/ ANALYZE/ ALTER TABLE/VALIDATE/ VACUUM(not full)	避免并发schema changes 和VACUUM
SHARE			×	×		×	×	×	CREATE INDEX（without CURRENTLY）	避免并发data changes
SHARE ROW EXCLUSIVE		×	×	×	×	×	×	×	CREATE TRIGGER	避免并发data changes，并且是self-exclusive 的，同一时间只能有一个session持有该锁
EXCLUSIVE		×	×	×	×	×	×	×	REFRESH MATERIALIZED VIEW CONCURRENTLY
ACCESS EXCLUSIVE	×	×	×	×	×	×	×	×	DROP/TRUNCATE/REINDEX/CLUSTER VACUUM FULL等	同一时间只允许一个session持有，prevents concurrent transactions from reading and writeing

应用层并发控制