Types of Locks

Yellowbrick provides various lock modes to control concurrent access to data in tables. The list of Table Level Locks is given below:

Table Level Locks

Access Share (AccessShareLock)

The SELECT command acquires a lock of this mode on referenced tables. In general, any query that only reads a table and does not modify it will acquire this lock mode.

Share Update Exclusive (ShareUpdateExclusiveLock)

Acquired by VACUUM (without FULL), ANALYZE,UPDATE and ALTER TABLE variants. This mode protects a table against concurrent schema changes and VACUUM runs.

Access Exclusive (AccessExclusiveLock)

Acquired by the DROP TABLE, TRUNCATE. ALTER TABLE also acquire a lock at this level. This mode guarantees that the holder is the only transaction accessing the table in any way.

Row Exclusive (RowExclusiveLock)

The commands UPDATE, DELETE and INSERTacquire this lock mode on the target table. In general, this lock mode will be acquired by any command that modifies data in a table.

Conflicting Table Level Lock Modes