On 8th of February, Simon Riggs committed patch:
Extend ALTER TABLE TO allow FOREIGN KEYS TO be added WITHOUT initial validation. FK constraints that are marked NOT VALID may later be VALIDATED, which uses an ShareUpdateExclusiveLock ON CONSTRAINT TABLE AND RowShareLock ON referenced TABLE. Significantly reduces LOCK strength AND duration WHEN adding FKs. NEW state visible FROM psql. Simon Riggs, WITH reviews FROM Marko Tiikkaja AND Robert Haas
On 28th of July, Simon Riggs committed patch which:
Log Message: ----------- Reduce LOCK levels OF CREATE TRIGGER AND SOME ALTER TABLE, CREATE RULE actions. Avoid hard-coding lockmode used FOR many altering DDL commands, allowing easier future changes OF LOCK levels. Implementation OF initial analysis ON DDL sub-commands, so that many LOCK levels are now at ShareUpdateExclusiveLock OR ShareRowExclusiveLock, allowing certain DDL NOT TO block reads/writes. FIRST OF NUMBER OF planned changes IN this area; additional docs required WHEN FULL project complete.
Continue reading Waiting for 9.1 – Reduced lock levels for ALTER TABLE