PostgreSQL 9.6 统计信息收集进程pgstat，增加了等待事件信息的收集，并且用户可以获得backend的等待事件信息。
目前支持的等待事件分类如下
src/include/pgstat.h
/* ----------
* Wait Classes
* ----------
*/
typedef enum WaitClass
{
WAIT_UNDEFINED,
WAIT_LWLOCK_NAMED,
WAIT_LWLOCK_TRANCHE,
WAIT_LOCK,
WAIT_BUFFER_PIN
} WaitClass;支持的获取等待事件类别和等待事件信息的函数
src/backend/postmaster/pgstat.c
/* ----------
* pgstat_get_wait_event_type() -
*
* Return a string representing the current wait event type, backend is
* waiting on.
*/
const char *
pgstat_get_wait_event_type(uint32 wait_event_info)
{
uint8 classId;
const char *event_type;
/* report process as not waiting. */
if (wait_event_info == 0)
return NULL;
wait_event_info = wait_event_info >> 24;
classId = wait_event_info & 0XFF;
switch (classId)
{
case WAIT_LWLOCK_NAMED:
event_type = "LWLockNamed";
break;
case WAIT_LWLOCK_TRANCHE:
event_type = "LWLockTranche";
break;
case WAIT_LOCK:
event_type = "Lock";
break;
case WAIT_BUFFER_PIN:
event_type = "BufferPin";
break;
default:
event_type = "???";
break;
}
return event_type;
}
/* ----------
* pgstat_get_wait_event() -
*
* Return a string representing the current wait event, backend is
* waiting on.
*/
const char *
pgstat_get_wait_event(uint32 wait_event_info)
{
uint8 classId;
uint16 eventId;
const char *event_name;
/* report process as not waiting. */
if (wait_event_info == 0)
return NULL;
eventId = wait_event_info & ((1 << 24) - 1);
wait_event_info = wait_event_info >> 24;
classId = wait_event_info & 0XFF;
switch (classId)
{
case WAIT_LWLOCK_NAMED:
case WAIT_LWLOCK_TRANCHE:
event_name = GetLWLockIdentifier(classId, eventId);
break;
case WAIT_LOCK:
event_name = GetLockNameFromTagType(eventId);
break;
case WAIT_BUFFER_PIN:
event_name = "BufferPin";
break;
default:
event_name = "unknown wait event";
break;
}
return event_name;
}
详细的等待信息归类和信息见手册
https://www.postgresql.org/docs/9.6/static/monitoring-stats.html
在pg_stat_activity动态视图中支持的等待事件字段信息如下
wait_event_type
The type of event for which the backend is waiting, if any; otherwise NULL.
Possible values are:
LWLockNamed:
The backend is waiting for a specific named lightweight lock. Each such lock protects a particular data structure in shared memory. wait_event will contain the name of the lightweight lock.
LWLockTranche:
The backend is waiting for one of a group of related lightweight locks. All locks in the group perform a similar function; wait_event will identify the general purpose of locks in that group.
Lock:
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.
BufferPin:
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.wait_event
Wait event name if backend is currently waiting, otherwise NULL.
See wait_event for details.等待事件的归类以及对应的等待信息解释
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.
