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This clause changes the behavior of SELECT locking clauses in the presence of locked rows: instead of causing a process to block waiting for the locks held by other processes (or raise an error, with NOWAIT), SKIP LOCKED makes the new reader skip over such rows. While this is not appropriate behavior for general purposes, there are some cases in which it is useful, such as queue-like tables. Catalog version bumped because this patch changes the representation of stored rules. Reviewed by Craig Ringer (based on a previous attempt at an implementation by Simon Riggs, who also provided input on the syntax used in the current patch), David Rowley, and Álvaro Herrera. Author: Thomas Munro
31 lines
950 B
C
31 lines
950 B
C
/*-------------------------------------------------------------------------
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* lockwaitpolicy.h
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* Header file for LockWaitPolicy enum.
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*
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* Copyright (c) 2014, PostgreSQL Global Development Group
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*
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* src/include/utils/lockwaitpolicy.h
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*-------------------------------------------------------------------------
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*/
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#ifndef LOCKWAITPOLICY_H
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#define LOCKWAITPOLICY_H
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/*
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* This enum controls how to deal with rows being locked by FOR UPDATE/SHARE
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* clauses (i.e., NOWAIT and SKIP LOCKED clauses). The ordering here is
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* important, because the highest numerical value takes precedence when a
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* RTE is specified multiple ways. See applyLockingClause.
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*/
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typedef enum
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{
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/* Wait for the lock to become available (default behavior) */
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LockWaitBlock,
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/* Skip rows that can't be locked (SKIP LOCKED) */
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LockWaitSkip,
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/* Raise an error if a row cannot be locked (NOWAIT) */
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LockWaitError
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} LockWaitPolicy;
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#endif /* LOCKWAITPOLICY_H */
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