Waiting for a read from a replication slot control file. Waiting to apply WAL at recovery because it is delayed. PostgreSQL is one of the most popular open-source databases in the world and has successful implementations across several mission-critical environments across various domains, using real-time high-end OLTP applications performing millions and billions of transactions per day. Time at which the last data page checksum failure was detected in this database (or on a shared object), or NULL if data checksums are not enabled. Waiting in main loop of WAL writer process. Waiting to read or update old snapshot control information. Waiting for the page number needed to continue a parallel B-tree scan to become available. Re: Improve WALRead() to suck data directly from WAL buffers when possible - Mailing list pgsql-hackers See, OID of the database this backend is connected to, Name of the database this backend is connected to, Name of the user logged into this backend, Name of the application that is connected to this backend. Waiting in main loop of syslogger process. Waiting for a write to a relation data file. finish their input/output (I/O) operations when concurrently trying to access a page. Waiting to receive bytes from a shared message queue. See, Time when the current transaction was started. The pg_stat_activity view will have one row per server process, showing information related to the current activity of that process. See, One row for each table in the current database, showing statistics about accesses to that specific table. to report a documentation issue. See, At least one row per subscription, showing information about the subscription workers. This documentation is for an unsupported version of PostgreSQL. Waiting for data to reach durable storage while adding a line to the data directory lock file. Returns the IP address of the client connected to this backend. Waiting for WAL files required for a backup to be successfully archived. Waiting for SLRU data to reach durable storage following a page write. Port number of the PostgreSQL instance this WAL receiver is connected to. Waiting to acquire a speculative insertion lock. Waiting in WAL receiver to establish connection to remote server. wait_event will identify the specific wait point. Waiting for a replication origin to become inactive to be dropped. Waiting to elect a Parallel Hash participant to allocate a hash table. If the state is active and wait_event is non-null, it means that a query is being executed, but is being blocked somewhere in the system. The pg_stat_ssl view will contain one row per backend or WAL sender process, showing statistics about SSL usage on this connection. In contrast, when starting from an unclean shutdown (e.g., after an immediate shutdown, a server crash, starting from a base backup, and point-in-time recovery), all statistics counters are reset. Waiting to insert WAL data into a memory buffer. A process acquires an LWLock in a shared mode to read from the buffer and . Waiting for a read during recheck of the data directory lock file. These numbers do not act as stated above; instead they update continuously throughout the transaction. The pg_statio_all_tables view will contain one row for each table in the current database (including TOAST tables), showing statistics about I/O on that specific table. Waiting to retrieve messages from the shared catalog invalidation queue. Waiting for stats dynamic shared memory allocator access, Waiting for stats shared memory hash table access, Waiting for shared memory stats data access. Avoid PostgreSQL LWLock:buffer_content locks in Amazon Aurora: Tips and Waiting for a replication slot control file to reach durable storage while restoring it to memory. See, One row only, showing statistics about the WAL archiver process's activity. Waiting for a relation data file to be truncated. Use partitioned tables (which also have partitioned indexes). 28.2. The Cumulative Statistics System - PostgreSQL Documentation Waiting for recovery conflict resolution for dropping a tablespace. a page) has to be retrieved outside the shared buffer pool. Waiting to replace a page in WAL buffers. Number of transactions in this database that have been committed, Number of transactions in this database that have been rolled back, Number of disk blocks read in this database, Number of times disk blocks were found already in the buffer cache, so that a read was not necessary (this only includes hits in the PostgreSQL buffer cache, not the operating system's file system cache), Number of live rows fetched by sequential scans and index entries returned by index scans in this database, Number of live rows fetched by index scans in this database, Number of rows inserted by queries in this database, Number of rows updated by queries in this database, Number of rows deleted by queries in this database, Number of queries canceled due to conflicts with recovery in this database. Per-Backend Statistics Functions, pg_stat_get_backend_idset () setof integer. Last write-ahead log location already received and written to disk, but not flushed. When the buffer manager receives a request, PostgreSQL uses the buffer_tag of the desired page. In particular, when the standby has caught up completely, pg_stat_replication shows the time taken to write, flush and replay the most recent reported WAL location rather than zero as some users might expect. This view will only contain information on standby servers, since conflicts do not occur on master servers. Resets statistics of the replication slot defined by the argument. BufferCacheHitRatio and LWLock:BufferIO wait Waiting to acquire an exclusive pin on a buffer. Possible values are: Top-level transaction identifier of this backend, if any. Waiting for a serialized historical catalog snapshot to reach durable storage. Waiting to access a shared tuple store during parallel query. Waiting in main loop of archiver process. LWLock: The backend is waiting for a lightweight lock. Waiting to read or update transaction commit timestamps. Waiting to read or update the replication progress. These files are stored in the directory named by the stats_temp_directory parameter, pg_stat_tmp by default. Number of transactions spilled to disk once the memory used by logical decoding to decode changes from WAL has exceeded logical_decoding_work_mem. These times represent the commit delay that was (or would have been) introduced by each synchronous commit level, if the remote server was configured as a synchronous standby. Waiting for a write of a timeline history file received via streaming replication. The pg_statio_user_tables and pg_statio_sys_tables views contain the same information, but filtered to only show user and system tables respectively. Returns the time when the backend's current transaction was started. LWLock:buffer_mapping. Resets statistics for a single function in the current database to zero. This is used by system processes waiting for activity in their main processing loop. The WALWriteLock wait occurs while PostgreSQL flushes WAL records to disk or during a WAL segment switch.. How to reduce this wait . So the statistics will show static information as long as you continue the current transaction. Waiting in main loop of syslogger process. To reduce confusion for users expecting a different model of lag, the lag columns revert to NULL after a short time on a fully replayed idle system. Waiting for the relation map file to reach durable storage. BK_1935: "IObuffer_locks,ControlLock()"IOControlLockControlLockIOSlruSharedData Activity: The server process is idle. potential: This standby server is now asynchronous, but can potentially become synchronous if one of current synchronous ones fails. Waiting for a read while adding a line to the data directory lock file. The easiest way to create a cross-Region replica for Amazon RDS for PostgreSQL is by completing the following steps: On the Amazon RDS console, choose your Amazon RDS for PostgreSQL source instance. Waiting for a write of a newly created timeline history file. The server process is waiting for a timeout to expire. Waiting for I/O on a commit timestamp SLRU buffer. Every PostgreSQL process collects statistics locally, then updates the shared data at appropriate intervals. Waiting for the page number needed to continue a parallel B-tree scan to become available. idle in transaction (aborted): This state is similar to idle in transaction, except one of the statements in the transaction caused an error. There are also several other views, listed in Table28.2, available to show the results of statistics collection. See, One row for each tracked function, showing statistics about executions of that function. The pg_stat_bgwriter view will always have a single row, containing global data for the cluster. Waiting in main loop of logical replication apply process. OID of the user logged into this WAL sender process, Name of the user logged into this WAL sender process, Name of the application that is connected to this WAL sender. The server process is waiting for exclusive access to a data buffer. Waiting for a two phase state file to reach durable storage. 5mins of Postgres E25: Postgres lock monitoring, LWLocks and the log See. However, current-query information collected by track_activities is always up-to-date. Number of times transactions were spilled to disk while decoding changes from WAL for this slot. Waits for a buffer pin ( BufferPin ). The pg_stat_slru view will contain one row for each tracked SLRU cache, showing statistics about access to cached pages. workload into more reader nodes. pg_stat_get_backend_client_port ( integer ) integer. The argument can be bgwriter to reset all the counters shown in the pg_stat_bgwriter view, archiver to reset all the counters shown in the pg_stat_archiver view, wal to reset all the counters shown in the pg_stat_wal view or recovery_prefetch to reset all the counters shown in the pg_stat_recovery_prefetch view. ), Reset some cluster-wide statistics counters to zero, depending on the argument (requires superuser privileges by default, but EXECUTE for this function can be granted to others). Before PostgreSQL 8.1, all operations of the shared buffer manager itself were protected by a single system-wide lock, the BufMgrLock, which unsurprisingly proved to be a source of contention.