Waiting for a serialized historical catalog snapshot to reach durable storage. In all other states, it shows the last query that was executed. The functions for per-function statistics take a function OID. For example, to show the PIDs and current queries of all backends: Table28.20. Waiting for a new WAL segment created by copying an existing one to reach durable storage. The next use of statistical information will cause a new snapshot to be fetched. Waiting to access the multixact member SLRU cache. Waiting for other Parallel Hash participants to finish hashing the inner relation. Waiting to read while creating the data directory lock file. Current WAL sender state. For client backends, this is the time the client connected to the server. Waiting to allocate a new transaction ID. Waiting to replace a page in WAL buffers. The pg_stat_wal_receiver view will contain only one row, showing statistics about the WAL receiver from that receiver's connected server. Number of disk blocks read from this table, Number of disk blocks read from all indexes on this table, Number of buffer hits in all indexes on this table, Number of disk blocks read from this table's TOAST table (if any), Number of buffer hits in this table's TOAST table (if any), Number of disk blocks read from this table's TOAST table indexes (if any), Number of buffer hits in this table's TOAST table indexes (if any). The function pg_stat_get_backend_idset provides a convenient way to generate one row for each active backend for invoking these functions. Waiting between writes while performing a checkpoint. Waiting for a serialized historical catalog snapshot to reach durable storage. Extensions can add LWLock types to the list shown in Table28.12. Waiting for a write while creating the data directory lock file. idle in transaction: The backend is in a transaction, but is not currently executing a query. If the standby server has entirely caught up with the sending server and there is no more WAL activity, the most recently measured lag times will continue to be displayed for a short time and then show NULL. The pg_statio_ views are primarily useful to determine the effectiveness of the buffer cache. Extensions can register their specific waits ( Extension ). If this field is null, it indicates that the client is connected via a Unix socket on the server machine. See Table28.4. When the number of actual disk reads is much smaller than the number of buffer hits, then the cache is satisfying most read requests without invoking a kernel call. Waiting for WAL from a stream at recovery. Waiting for a read while adding a line to the data directory lock file. finish their input/output (I/O) operations when concurrently trying to access a page. wait_event will identify the specific wait point. Waiting in WAL receiver to establish connection to remote server. Pointers to free buffers and to the next victim are protected by one buffer strategy lock spinlock. Waiting for the control file to reach durable storage. Using pg_stat_reset() also resets counters that autovacuum uses to determine when to trigger a vacuum or an analyze. Autovacuum worker or launcher waiting to update or read the current state of autovacuum workers. Please refer to your browser's Help pages for instructions. Waiting for other Parallel Hash participants to finish inserting tuples into new buckets. Resets all statistics counters for the current database to zero. ), 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). Waiting for parallel bitmap scan to become initialized. Time elapsed between flushing recent WAL locally and receiving notification that this standby server has written, flushed and applied it. This can be used to gauge the delay that, Time elapsed between flushing recent WAL locally and receiving notification that this standby server has written, flushed and applied it. Waiting for a write during reorder buffer management. See, One row per subscription, showing statistics about errors. A transaction can also see its own statistics (as yet untransmitted to the collector) in the views pg_stat_xact_all_tables, pg_stat_xact_sys_tables, pg_stat_xact_user_tables, and pg_stat_xact_user_functions. (See Chapter20 for details about setting configuration parameters.). Distinguished Name (DN) field from the client certificate used, or NULL if no client certificate was supplied or if SSL is not in use on this connection. Host name of the connected client, as reported by a reverse DNS lookup of client_addr. Waiting for a replication origin to become inactive to be dropped. Connection string used by this WAL receiver, with security-sensitive fields obfuscated. LWTRANCHE_BUFFER_CONTENT @ LWTRANCHE_BUFFER_CONTENT. pg_stat_get_activity, the underlying function of the pg_stat_activity view, returns a set of records containing all the available information about each backend process. Waiting in main loop of syslogger process. Waiting in main loop of checkpointer process. When a buffer is read from disk (or written to disk), an IO in progress lock is also acquired, which indicates to other processes that the page is being read (or written) they can queue up if they need to do something with this page. Principal used to authenticate this connection, or NULL if GSSAPI was not used to authenticate this connection. Waiting to elect a Parallel Hash participant to allocate more buckets. See, One row per database, showing database-wide statistics about query cancels due to conflict with recovery on standby servers. to keep index reordering low and reduces its impact. Waiting to read or update vacuum-related information for a B-tree index. This field is truncated if the principal is longer than NAMEDATALEN (64 characters in a standard build). This can be used to gauge the delay that synchronous_commit level remote_apply incurred while committing if this server was configured as a synchronous standby. This field is truncated if the DN field is longer than, Number of WAL files that have been successfully archived, Name of the last WAL file successfully archived, Time of the last successful archive operation, Number of failed attempts for archiving WAL files, Name of the WAL file of the last failed archival operation, Time of the last failed archival operation, Time at which these statistics were last reset, Number of scheduled checkpoints that have been performed, Number of requested checkpoints that have been performed, Total amount of time that has been spent in the portion of checkpoint processing where files are written to disk, in milliseconds, Total amount of time that has been spent in the portion of checkpoint processing where files are synchronized to disk, in milliseconds, Number of buffers written during checkpoints, Number of buffers written by the background writer, Number of times the background writer stopped a cleaning scan because it had written too many buffers, Number of buffers written directly by a backend, Number of times a backend had to execute its own. Lag times work automatically for physical replication. Its purpose is for the same page to be read into the shared buffer. See, One row for each table in the current database, showing statistics about accesses to that specific table. Waiting for SLRU data to reach durable storage following a page write. By default the query text is truncated at 1024 bytes; this value can be changed via the parameter track_activity_query_size. wait_event will identify the specific wait point. Waiting for other Parallel Hash participants to finish loading a hash table. The pg_stat_bgwriter view will always have a single row, containing global data for the cluster. Waiting to read or update multixact offset mappings. Such a system would show similar times while new WAL is being generated, but would differ when the sender becomes idle. Waiting for base backup to read from a file. The pg_stat_bgwriter view will always have a single row, containing global data for the cluster. pg_blocking_pids function. pg_stat_get_backend_userid ( integer ) oid. Waiting to retrieve messages from the shared catalog invalidation queue. Waiting for an update to the control file to reach durable storage. Postgres Locking: When is it Concerning? Amount of transaction data decoded for sending transactions to the decoding output plugin while decoding changes from WAL for this slot. You can split your catchup: This WAL sender's connected standby is catching up with the primary. PostgreSQL's cumulative statistics system supports collection and reporting of information about server activity. Waiting for mapping data to reach durable storage during a logical rewrite. Waiting for a buffered file to be truncated. Waiting for a read of a timeline history file. Resets statistics for a single table or index in the current database or shared across all databases in the cluster to zero. Waiting to read or update the state of prepared transactions. But access to that shared memory requires the protection of light-weight locks, which should last for only nanoseconds or microseconds while the memory access is actually occuring. This can be a host name, an IP address, or a directory path if the connection is via Unix socket. Time elapsed between flushing recent WAL locally and receiving notification that this standby server has written it (but not yet flushed it or applied it). Waiting for I/O on an async (notify) buffer. See, One row per database, showing database-wide statistics about query cancels due to conflict with recovery on standby servers. Listen The most possible reason for why you see LWLockTranche/buffer_mapping wait event in PostgreSQL Well, if you are here you probably came across an issue where your database had CPU spikes. What we have discussed in this episode of 5mins of Postgres. It also tracks the total number of rows in each table, and information about vacuum and analyze actions for each table. If the argument is NULL, all counters shown in the pg_stat_slru view for all SLRU caches are reset. Waiting to read or update dynamic shared memory allocation information. Lock: The backend is waiting for a heavyweight lock. The parameter track_io_timing enables monitoring of block read and write times. (For example, in psql you could issue \d+ pg_stat_activity.) Waiting for an elected Parallel Hash participant to decide on future batch growth. BK_1935: "IObuffer_locks,ControlLock()"IOControlLockControlLockIOSlruSharedData LWLock- buffer_mapping. See, One row for each backend (including autovacuum worker processes) running, One row for each WAL sender process streaming a base backup, showing current progress. (The path case can be distinguished because it will always be an absolute path, beginning with /.). The pg_statio_all_sequences view will contain one row for each sequence in the current database, showing statistics about I/O on that specific sequence. Waiting in main loop of background writer process. This counts top-level transactions only, and is not incremented for subtransactions. checksum_last_failure timestamp with time zone. The server process is waiting for a heavyweight lock. Current overall state of this backend. This lock is used to handle multiple sessions that all require access to the same Waiting to manage an extension's space allocation in shared memory. The pg_stat_user_tables and pg_stat_sys_tables views contain the same information, but filtered to only show user and system tables respectively. Timeout: The server process is waiting for a timeout to expire.