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pg_stat_activity View explanation in postgresSql

The pg_stat_activity view will have one row per server process, showing information related to the current activity of that process.

Note: The waiting and state columns are independent. If a backend is in the active state, it may or may not be waiting. If the state is active and waiting is true, it means that a query is being executed, but is being blocked by a lock somewhere in the system.

Column
Type
Description
datid
oid
OID of the database this backend is connected to
datname
name
Name of the database this backend is connected to
pid
integer
Process ID of this backend
usesysid
oid
OID of the user logged into this backend
usename
name
Name of the user logged into this backend
application_name
text
Name of the application that is connected to this backend
client_addr
inet
IP address of the client connected to this backend. If this field is null, it indicates either that the client is connected via a Unix socket on the server machine or that this is an internal process such as autovacuum.
client_hostname
text
Host name of the connected client, as reported by a reverse DNS lookup of client_addr. This field will only be non-null for IP connections, and only when log_hostname is enabled.
client_port
integer
TCP port number that the client is using for communication with this backend, or -1 if a Unix socket is used
backend_start
timestamp with time zone
Time when this process was started, i.e., when the client connected to the server
xact_start
timestamp with time zone
Time when this process' current transaction was started, or null if no transaction is active. If the current query is the first of its transaction, this column is equal to the query_start column.
query_start
timestamp with time zone
Time when the currently active query was started, or if state is not active, when the last query was started
state_change
timestamp with time zone
Time when the state was last changed
wait_event_type
text
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_eventwill 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
text
Wait event name if backend is currently waiting, otherwise NULL. See Table 28-4 for details.
state
text
Current overall state of this backend. Possible values are:
  • active: The backend is executing a query.
  • idle: The backend is waiting for a new client command.
  • idle in transaction: The backend is in a transaction, but is not currently executing a query.
  • idle in transaction (aborted): This state is similar to idle in transaction, except one of the statements in the transaction caused an error.
  • fastpath function call: The backend is executing a fast-path function.
  • disabled: This state is reported if track_activities is disabled in this backend.
backend_xid
xid
Top-level transaction identifier of this backend, if any.
backend_xmin
xid
The current backend's xmin horizon.
query
text
Text of this backend's most recent query. If state is active this field shows the currently executing query. In all other states, it shows the last query that was executed.
The pg_stat_activity view will have one row per server process, showing information related to the current activity of that process.
Note: The wait_event and state columns are independent. If a backend is in the activestate, it may or may not be waiting on some event. If the state is active and wait_eventis non-null, it means that a query is being executed, but is being blocked somewhere in the system.
current running query find out
database1=# SELECT count(*) as cnt, usename, current_query FROM pg_stat_activity GROUP BY usename,current_query ORDER BY cnt DESC;

 cnt |    usename    | current_query
-----+---------------+---------------
   7 | freddykrueger | <IDLE>
   3 | freddykrueger | SELECT name FROM users WHERE id=50;
   1 | postgres      | <IDLE>
(3 rows)
Here is an example of how wait events can be viewed
SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event is NOT NULL;
 pid  | wait_event_type |  wait_event
------+-----------------+---------------
 2540 | Lock            | relation
 6644 | LWLockNamed     | ProcArrayLock
(2 rows)
Note: For tranches registered by extensions, the name is specified by extension and this will be displayed as wait_event. It is quite possible that user has registered the tranche in one of the backends (by having allocation in dynamic shared memory) in which case other backends won't have that information, so we display extension for such cases.
wait_event Description:
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 B-tree 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.
OldSnapshotTimeMapLock
Waiting to read or update old snapshot control 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.

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