Postgresql 锁查看

之前版本 PostgreSQL 的 pg_stat_activity 视图的 waiting 字段判断会话是否等待锁资源（通俗地讲， waiting 值为true表示申请不到锁资源处于等待状态），但是并不会给出具体的锁的信息，9.6 版本之后 pg_stat_activity 视图的 waiting 字段被 wait_event_type 和 wait_event 字段取代，这两个字段分别代表等待事件的类型、等待事件名称；

SELECT pid, wait_event_type, wait_event FROM pg_stat_activity；

Wait Event Type	Wait Event Name	Description
LWLockNamed	ShmemIndexLock	Waiting to find or allocate space in shared memory.
	OidGenLock	Waiting to allocate or assign an OID.
	XidGenLock	Waiting to allocate or assign a transaction id.
	ProcArrayLock	Waiting to get a snapshot or clearing a transaction id at transaction end.
	SInvalReadLock	Waiting to retrieve or remove messages from shared invalidation queue.
	SInvalWriteLock	Waiting to add a message in shared invalidation queue.
	WALBufMappingLock	Waiting to replace a page in WAL buffers.
	WALWriteLock	Waiting for WAL buffers to be written to disk.
	ControlFileLock	Waiting to read or update the control file or creation of a new WAL file.
	CheckpointLock	Waiting to perform checkpoint.
	CLogControlLock	Waiting to read or update transaction status.
	SubtransControlLock	Waiting to read or update sub-transaction information.
	MultiXactGenLock	Waiting to read or update shared multixact state.
	MultiXactOffsetControlLock	Waiting to read or update multixact offset mappings.
	MultiXactMemberControlLock	Waiting to read or update multixact member mappings.
	RelCacheInitLock	Waiting to read or write relation cache initialization file.
	CheckpointerCommLock	Waiting to manage fsync requests.
	TwoPhaseStateLock	Waiting to read or update the state of prepared transactions.
	TablespaceCreateLock	Waiting to create or drop the tablespace.
	BtreeVacuumLock	Waiting to read or update vacuum-related information for a Btree index.
	AddinShmemInitLock	Waiting to manage space allocation in shared memory.
	AutovacuumLock	Autovacuum worker or launcher waiting to update or read the current state of autovacuum workers.
	AutovacuumScheduleLock	Waiting to ensure that the table it has selected for a vacuum still needs vacuuming.
	SyncScanLock	Waiting to get the start location of a scan on a table for synchronized scans.
	RelationMappingLock	Waiting to update the relation map file used to store catalog to filenode mapping.
	AsyncCtlLock	Waiting to read or update shared notification state.
	AsyncQueueLock	Waiting to read or update notification messages.
	SerializableXactHashLock	Waiting to retrieve or store information about serializable transactions.
	SerializableFinishedListLock	Waiting to access the list of finished serializable transactions.
	SerializablePredicateLockListLock	Waiting to perform an operation on a list of locks held by serializable transactions.
	OldSerXidLock	Waiting to read or record conflicting serializable transactions.
	SyncRepLock	Waiting to read or update information about synchronous replicas.
	BackgroundWorkerLock	Waiting to read or update background worker state.
	DynamicSharedMemoryControlLock	Waiting to read or update dynamic shared memory state.
	AutoFileLock	Waiting to update the postgresql.auto.conf file.
	ReplicationSlotAllocationLock	Waiting to allocate or free a replication slot.
	ReplicationSlotControlLock	Waiting to read or update replication slot state.
	CommitTsControlLock	Waiting to read or update transaction commit timestamps.
	CommitTsLock	Waiting to read or update the last value set for the transaction timestamp.
	ReplicationOriginLock	Waiting to setup, drop or use replication origin.
	MultiXactTruncationLock	Waiting to read or truncate multixact information.
LWLockTranche	clog	Waiting for I/O on a clog (transaction status) buffer.
	commit_timestamp	Waiting for I/O on commit timestamp buffer.
	subtrans	Waiting for I/O a subtransaction buffer.
	multixact_offset	Waiting for I/O on a multixact offset buffer.
	multixact_member	Waiting for I/O on a multixact_member buffer.
	async	Waiting for I/O on an async (notify) buffer.
	oldserxid	Waiting to I/O on an oldserxid buffer.
	wal_insert	Waiting to insert WAL into a memory buffer.
	buffer_content	Waiting to read or write a data page in memory.
	buffer_io	Waiting for I/O on a data page.
	replication_origin	Waiting to read or update the replication progress.
	replication_slot_io	Waiting for I/O on a replication slot.
	proc	Waiting to read or update the fast-path lock information.
	buffer_mapping	Waiting to associate a data block with a buffer in the buffer pool.
	lock_manager	Waiting to add or examine locks for backends, or waiting to join or exit a locking group (used by parallel query).
	predicate_lock_manager	Waiting to add or examine predicate lock information.
Lock	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	BufferPin	Waiting to acquire a pin on a buffer.

 

备注：通过以上表格， wait_event_type 主要分类四类：

• LWLockNamed：表示backend后台进程等待某种特定的轻量级锁；
• LWLockTranche：表示backend后台进程等待一组相关轻量级锁；
• Lock：表示backend后台进程等待重量级的锁，通常是指 relation、tuple、page、transactionid 等子类型锁；
• BufferPin：表示server process 后台进程等待 buffer pin，手册上解释为 Waiting to acquire a pin on a buffer，比较难理解，以后想想如何模拟此场景。