PostgreSQL V9.6 LWLock实现分析(三)

表X-XX

Wait Event Type

Wait Event Name

Description

Lock[1]	relation	Waiting to acquire a lock on a relation.
	extend	Waiting to extend a relation.
	page	Waiting to acquire a lock on page of a relation.
	tuple	Waiting to acquire a lock on a tuple.
	transactionid	Waiting for a transaction to finish.
	virtualxid	Waiting to acquire a virtual xid lock.
	speculative token	Waiting to acquire a speculative insertion lock.
	object	Waiting to acquire a lock on a non-relation database object.
	userlock	Waiting to acquire a userlock.
	advisory	Waiting to acquire an advisory user lock.
BufferPin[2]	BufferPin	Waiting to acquire a pin on a buffer.

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[1] The backend is waiting for a heavyweight lock. Heavyweight locks, also known as lock manager locks or simply locks, primarily protect SQL-visible objects such as tables. However, they are also used to ensure mutual exclusion for certain internal operations such as relation extension. wait_event will identify the type of lock awaited.

[2] The server process is waiting to access to a data buffer during a period when no other process can be examining that buffer. Buffer pin waits can be protracted if another process holds an open cursor which last read data from the buffer in question