gorthx on Twitter pg_stat_get_backend_activity ( integer ) text. The pg_statio_user_indexes and pg_statio_sys_indexes views contain the same information, but filtered to only show user and system indexes respectively. Waiting to read or update information about synchronous replicas. , LWTRANCHE_MXACTMEMBER_BUFFERS, LWTRANCHE_ASYNC_BUFFERS, LWTRANCHE_OLDSERXID_BUFFERS, LWTRANCHE_WAL_INSERT, LWTRANCHE_BUFFER_CONTENT, LWTRANCHE_BUFFER_IO_IN_PROGRESS, LWTRANCHE . Waiting in main loop of WAL receiver process. This includes the sync time when wal_sync_method is either open_datasync or open_sync. The server process is waiting for a lightweight lock. Waiting for data to reach durable storage while assigning a new WAL sync method. The parameter track_wal_io_timing enables monitoring of WAL write times. proc: Waiting to read or update the fast-path lock information. Presently, accesses to tables and indexes in both disk-block and individual-row terms are counted. Number of temporary files created by queries in this database. The pg_stat_bgwriter view will always have a single row, containing global data for the cluster. Waiting to acquire a speculative insertion lock. Waiting to update limit on notification message storage. This is consistent with the goal of measuring synchronous commit and transaction visibility delays for recent write transactions. Therefore, a bitmap scan increments the pg_stat_all_indexes.idx_tup_read count(s) for the index(es) it uses, and it increments the pg_stat_all_tables.idx_tup_fetch count for the table, but it does not affect pg_stat_all_indexes.idx_tup_fetch. See, One row for each table in the current database, showing statistics about accesses to that specific table. Waiting to read or update background worker state. It works like this: There are also several other views, listed in Table28.2, available to show the results of statistics collection. Waiting to read or update the state of logical replication workers. The columns wal_distance, block_distance and io_depth show current values, and the other columns show cumulative counters that can be reset with the pg_stat_reset_shared function. Table28.26.pg_stat_database_conflicts View, Number of queries in this database that have been canceled due to dropped tablespaces, Number of queries in this database that have been canceled due to lock timeouts, Number of queries in this database that have been canceled due to old snapshots, Number of queries in this database that have been canceled due to pinned buffers, Number of queries in this database that have been canceled due to deadlocks. The function pg_stat_get_backend_idset provides a convenient way to generate one row for each active backend for invoking these functions. 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 rows returned by queries in this database, Number of rows fetched by queries 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. being read from storage. See, Time when the current transaction was started. Waiting for a read during recheck of the data directory lock file. Waiting to access a shared tuple store during parallel query. The pg_statio_all_indexes view will contain one row for each index in the current database, showing statistics about I/O on that specific index. See, One row for each index in the current database, showing statistics about I/O on that specific index. idle in transaction: The backend is in a transaction, but is not currently executing a query. lock_manager Each such lock protects a particular data structure in shared memory. Resetting these counters can cause autovacuum to not perform necessary work, which can cause problems such as table bloat or out-dated table statistics. Amount of transaction data decoded for sending transactions to the decoding output plugin while decoding changes from WAL for this slot. Waiting for a write of a timeline history file received via streaming replication. Waiting for a new WAL segment created by copying an existing one to reach durable storage. Resets statistics for a single table or index in the current database or shared across all databases in the cluster to zero. The pg_stat_database view will contain one row for each database in the cluster, plus one for shared objects, showing database-wide statistics. David Christensen on Twitter. Possible values are: Last write-ahead log location sent on this connection, Last write-ahead log location written to disk by this standby server, Last write-ahead log location flushed to disk by this standby server, Last write-ahead log location replayed into the database on this standby server, 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 to ensure that a table selected for autovacuum still needs vacuuming. The pg_stat_ssl view will contain one row per backend or WAL sender process, showing statistics about SSL usage on this connection. Waiting to access the multixact member SLRU cache. Lock: The backend is waiting for a heavyweight lock. Resets statistics for a single function in the current database to zero. For an asynchronous standby, the replay_lag column approximates the delay before recent transactions became visible to queries. Waiting to access the shared per-process data structures (typically, to get a snapshot or report a session's transaction ID). Synchronous state of this standby server. OID of the database this backend is connected to, Name of the database this backend is connected to. Waiting for a write when creating a new WAL segment by copying an existing one. Discards the current statistics snapshot or cached information. This has no effect in a quorum-based synchronous replication. Waiting for the page number needed to continue a parallel B-tree scan to become available. The pg_stat_database view will contain one row for each database in the cluster, showing database-wide statistics. Waiting to write a protocol message to a shared message queue. Normally, WAL files are archived in order, oldest to newest, but that is not guaranteed, and does not hold under special circumstances like when promoting a standby or after crash recovery. In such cases, an older set of per-backend statistics access functions can be used; these are shown in Table28.20. Waiting to elect a Parallel Hash participant to allocate more batches. ), 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 to retrieve messages from the shared catalog invalidation queue. If state is active this field shows the currently executing query. Returns the OID of the database this backend is connected to. See. See Table28.4. Thanks for letting us know this page needs work. This field is truncated like client_dn. These numbers do not act as stated above; instead they update continuously throughout the transaction. Waiting for WAL buffers to be written to disk. Each buffer header also contains an LWLock, the "buffer content lock", that *does* represent the right to access the data: in the buffer. Waiting to perform an operation on a list of locks held by serializable transactions. Copyright 1996-2023 The PostgreSQL Global Development Group, PostgreSQL 15.2, 14.7, 13.10, 12.14, and 11.19 Released, 28.2.1. Priority of this standby server for being chosen as the synchronous standby in a priority-based synchronous replication. Similarly, information about the current queries of all sessions is collected when any such information is first requested within a transaction, and the same information will be displayed throughout the transaction. Host name of the connected client, as reported by a reverse DNS lookup of, TCP port number that the client is using for communication with this backend, or. Extensions can register their specific waits ( Extension ). Waiting for the page number needed to continue a parallel B-tree scan to become available. These files are stored in the directory named by the stats_temp_directory parameter, pg_stat_tmp by default. The server process is waiting for activity on a socket connected to a user application. For details such as the functions' names, consult the definitions of the standard views. Waiting to acquire a lock on a non-relation database object. operations, Large or bloated indexes that require the engine to read more pages than necessary into the shared buffer pool, Lack of indexes that forces the DB engine to read more pages from the tables than necessary, Checkpoints occurring too frequently or needing to flush too many modified pages, Sudden spikes for database connections trying to perform operations on the same page. Waiting in main loop of logical replication launcher process. Waiting for data to reach durable storage while adding a line to the data directory lock file. Waiting in main loop of logical replication apply process. Here is an example of how wait events can be viewed: The pg_stat_replication view will contain one row per WAL sender process, showing statistics about replication to that sender's connected standby server. Waiting for a WAL file to reach durable storage. When using the cumulative statistics views and functions to monitor collected data, it is important to realize that the information does not update instantaneously. The pg_stat_user_indexes and pg_stat_sys_indexes views contain the same information, but filtered to only show user and system indexes respectively. Postgres Locking: When is it Concerning? pg_stat_get_backend_client_port ( integer ) integer. Waiting for I/O on a multixact offset SLRU buffer. (For example, in psql you could issue \d+ pg_stat_activity.) The server process is idle. Other ways of looking at the statistics can be set up by writing queries that use the same underlying statistics access functions used by the standard views shown above. TCP port number that the client is using for communication with this WAL sender, or, Time when this process was started, i.e., when the client connected to this WAL sender. Waiting for startup process to send initial data for streaming replication. (To prevent ordinary users from hiding their activity from the administrator, only superusers are allowed to change these parameters with SET.). Last write-ahead log location already received and written to disk, but not flushed. Amount of decoded transaction data spilled to disk while performing decoding of changes from WAL for this slot. Logical decoding plugins may optionally emit tracking messages; if they do not, the tracking mechanism will simply display NULL lag. Waiting for activity from a child process while executing a. Waiting for a write of a serialized historical catalog snapshot. Waiting for an elected Parallel Hash participant to decide on future batch growth. Type of current backend. The functions for per-function statistics take a function OID. . Waiting for truncate of mapping data during a logical rewrite. See Table28.5 through Table28.13. Waiting for a read during reorder buffer management. See, One row per WAL sender process, showing statistics about replication to that sender's connected standby server. Waiting for background worker to shut down. 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. Waiting to retrieve or remove messages from shared invalidation queue. Waiting for a read during reorder buffer management. Waiting for a write during a file copy operation. 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. Waiting to find or allocate space in shared memory. LWLock:BufferIO. Please refer to your browser's Help pages for instructions. Lag times work automatically for physical replication. Waiting between writes while performing a checkpoint. This is consistent with the goal of measuring synchronous commit and transaction visibility delays for recent write transactions. Waiting in main loop of logical apply process. Thus, the server expects something to happen that is independent of its internal processes. Waiting in main loop of the archiver process. Waiting to add a message in shared invalidation queue. From the Actions drop-down menu, choose Create Read Replica. Monitoring systems should choose whether to represent this as missing data, zero or continue to display the last known value. PostgreSQL 's statistics collector is a subsystem that supports collection and reporting of information about server activity. Waiting for a serialized historical catalog snapshot to reach durable storage. Use partitioned tables (which also have partitioned indexes). Waiting for a relation data file to be extended. Verify whether you have unused indexes, then remove them. For example, to show the PIDs and current queries of all backends: Table28.20. Waiting in main loop of background writer process background worker. Number of backends currently connected to this database, or NULL for shared objects. Postgres Source Code Docs: Locking Overview. Waiting for a replication slot control file to reach durable storage. Ordinary users can only see all the information about their own sessions (sessions belonging to a role that they are a member of). Waiting to read or update vacuum-related information for a B-tree index. Waiting to elect a Parallel Hash participant to allocate more buckets. Waiting to access the list of finished serializable transactions. pg_stat_get_activity ( integer ) setof record. > However, someone with deeper knowledge of page pinning and buffer manager > internals could certainly devise a better solution. Waiting for a read while adding a line to the data directory lock file. 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. The latter will be less if any dead or not-yet-committed rows are fetched using the index, or if any heap fetches are avoided by means of an index-only scan. 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. See, One row for each tracked function, showing statistics about executions of that function. Number of blocks zeroed during initializations, Number of times disk blocks were found already in the SLRU, so that a read was not necessary (this only includes hits in the SLRU, not the operating system's file system cache), Number of disk blocks written for this SLRU, Number of blocks checked for existence for this SLRU, Number of flushes of dirty data for this SLRU. Waiting to allocate or assign a transaction id. Waiting to read or update shared multixact state. Increase the number of wal_buffers available to the database. finish their input/output (I/O) operations when concurrently trying to access a page. I am not the DBA, but receive reports occasionally when an application is causing load on the system. 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 read or update the fast-path lock information. disabled: This state is reported if track_activities is disabled in this backend. 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. Waiting for a write of a WAL page during bootstrapping. Waiting for other Parallel Hash participants to finish partitioning the outer relation. The server process is waiting for some condition defined by an extension module. 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. See Table28.5 through Table28.13. pg_stat_get_backend_xact_start ( integer ) timestamp with time zone. Waiting to replace a page in WAL buffers. If the argument is NULL, reset statistics for all subscriptions. If this field is null, it indicates that the client is connected via a Unix socket on the server machine. Calling, Reset statistics for a single table or index in the current database to zero (requires superuser privileges by default, but EXECUTE for this function can be granted to others), Reset statistics for a single function in the current database to zero (requires superuser privileges by default, but EXECUTE for this function can be granted to others), Set of currently active backend ID numbers (from 1 to the number of active backends), Time when the most recent query was started, IP address of the client connected to this backend, TCP port number that the client is using for communication, Wait event type name if backend is currently waiting, otherwise NULL. 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 data to reach durable storage while creating the data directory lock file. See. Waiting for a write while initializing a new WAL file. These access functions use a backend ID number, which ranges from one to the number of currently active backends. The pg_stat_ssl view will contain one row per backend or WAL sender process, showing statistics about SSL usage on this connection. In such cases, an older set of per-backend statistics access functions can be used; these are shown in Table28.35. Presently, the collector can count accesses to tables and indexes in both disk-block and individual-row terms. However, current-query information collected by track_activities is always up-to-date. Sometimes it may be more convenient to obtain just a subset of this information. Buffer pin waits can be protracted if another process holds an open cursor that last read data from the buffer in question. Waiting to send bytes to a shared message queue. This lock is used to handle multiple sessions that all require access to the same Waiting to replace a page in WAL buffers. The LWLock that this article will introduce is a lightweight lock (Lightweight Lock) based on SpinLock. Waiting for any activity when processing replies from WAL receiver in WAL sender process. The pg_stat_user_functions view will contain one row for each tracked function, showing statistics about executions of that function. Waiting to access the multixact offset SLRU cache. Returns the IP address of the client connected to this backend. Waiting for the group leader to clear the transaction ID at end of a parallel operation. * The BM_IO_IN_PROGRESS flag acts as a kind of lock, used to wait for I/O on a: buffer to complete (and in releases before 14, it was accompanied by a: per-buffer LWLock). Possible values are: async: This standby server is asynchronous. pg_stat_get_backend_dbid ( integer ) oid. Topics Relevant engine versions Context Causes Actions Relevant engine versions A process acquires an LWLock in a shared mode to read from the buffer and an exclusive mode to write to the buffer. Waiting in a cost-based vacuum delay point. See, Only one row, showing statistics about the WAL receiver from that receiver's connected server. PostgreSQL also supports reporting dynamic information about exactly what is going on in the system right now, such as the exact command currently being executed by other server processes, and which other connections exist in the system. Each individual server process flushes out accumulated statistics to shared memory just before going idle, but not more frequently than once per PGSTAT_MIN_INTERVAL milliseconds (1 second unless altered while building the server); so a query or transaction still in progress does not affect the displayed totals and the displayed information lags behind actual activity. Waiting for a read when creating a new WAL segment by copying an existing one. Waiting in WAL receiver to establish connection to remote server. The pg_stat_subscription view will contain one row per subscription for main worker (with null PID if the worker is not running), and additional rows for workers handling the initial data copy of the subscribed tables. Waiting to acquire an exclusive pin on a buffer. You By default the query text is truncated at 1024 bytes; this value can be changed via the parameter track_activity_query_size. Waiting to select the starting location of a synchronized table scan. Waiting for WAL to reach durable storage during bootstrapping. The argument can be one of CommitTs, MultiXactMember, MultiXactOffset, Notify, Serial, Subtrans, or Xact to reset the counters for only that entry. Top-level transaction identifier of this backend, if any. Using pg_stat_reset() also resets counters that autovacuum uses to determine when to trigger a vacuum or an analyze. Buffer pin waits can be protracted if another process holds an open cursor which last read data from the buffer in question. The IO:DataFileRead wait event occurs while data is Waiting to apply WAL during recovery because of a delay setting. Waiting to add a message to the shared catalog invalidation queue. Waiting for SSL while attempting connection. Here is an example of how wait events can be viewed. Its The reported lag times are not predictions of how long it will take for the standby to catch up with the sending server assuming the current rate of replay. This standby's xmin horizon reported by hot_standby_feedback. Waiting for stats dynamic shared memory allocator access, Waiting for stats shared memory hash table access, Waiting for shared memory stats data access. Waiting for a write while creating the data directory lock file. Waiting for a read from a relation data file. All temporary files are counted, regardless of why the temporary file was created (e.g., sorting or hashing), and regardless of the log_temp_files setting. Waiting for mapping data to reach durable storage during a logical rewrite. The latter will be less if any dead or not-yet-committed rows are fetched using the index, or if any heap fetches are avoided by means of an index-only scan. Waiting in main loop of WAL writer process. The pg_stat_database_conflicts view will contain one row per database, showing database-wide statistics about query cancels occurring due to conflicts with recovery on standby servers. The pg_stat_user_functions view will contain one row for each tracked function, showing statistics about executions of that function. Table28.19.pg_stat_subscription_stats View, Number of times an error occurred while applying changes, Number of times an error occurred during the initial table synchronization. Total amount of time spent writing WAL buffers to disk via XLogWrite request, in milliseconds (if track_wal_io_timing is enabled, otherwise zero). Indexes can be used by simple index scans, bitmap index scans, and the optimizer. Waiting to allocate or free a replication slot. Number of transactions spilled to disk once the memory used by logical decoding to decode changes from WAL has exceeded logical_decoding_work_mem. 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. For client backends, this is the time the client connected to the server. Definition: lwlock.h:190. potential: This standby server is now asynchronous, but can potentially become synchronous if one of current synchronous ones fails. See, Only one row, showing statistics about blocks prefetched during recovery. Re: Improve WALRead() to suck data directly from WAL buffers when possible - Mailing list pgsql-hackers 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 fsync call (normally the background writer handles those even when the backend does its own write). Serial number of the client certificate, or NULL if no client certificate was supplied or if SSL is not in use on this connection. (The path case can be distinguished because it will always be an absolute path, beginning with /.). Possible values are: Top-level transaction identifier of this backend, if any. Waiting to read or update the progress of one replication origin. See, At least one row per subscription, showing information about the subscription workers. Waiting in background writer process, hibernating. The server process is waiting for an I/O operation to complete. Waiting to read or update sub-transaction information. Waiting for a write of mapping data during a logical rewrite. If state is active this field shows the identifier of the currently executing query. Doing this helps Waiting to insert WAL into a memory buffer. IO: The server process is waiting for a IO to complete. streaming: This WAL sender is streaming changes after its connected standby server has caught up with the primary. This category is useful for modules to track custom waiting points. See Section30.5 for more information about the internal WAL function XLogWrite. streaming: This WAL sender is streaming changes after its connected standby server has caught up with the primary. Statistics Collection Configuration, One row per server process, showing information related to the current activity of that process, such as state and current query. fastpath function call: The backend is executing a fast-path function. The next use of statistical information will cause a new snapshot to be fetched. Waiting for a read from a replication slot control file. A process can wait for the data needed from a client ( Client) or another process ( IPC ). Waiting to send bytes to a shared message queue. Waiting to access the transaction status SLRU cache. Waiting for logical rewrite mappings to reach durable storage. Time when this process was started. In all other states, it shows the identifier of last query that was executed. Waiting to access predicate lock information used by serializable transactions. See, One row per subscription, showing statistics about errors. Waiting for activity from child process when executing. Extension: The server process is waiting for activity in an extension module. 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. See, One row per database, showing database-wide statistics. Table28.17.pg_stat_recovery_prefetch View, Number of blocks prefetched because they were not in the buffer pool, Number of blocks not prefetched because they were already in the buffer pool, Number of blocks not prefetched because they would be zero-initialized, Number of blocks not prefetched because they didn't exist yet, Number of blocks not prefetched because a full page image was included in the WAL, Number of blocks not prefetched because they were already recently prefetched, How many bytes ahead the prefetcher is looking, How many blocks ahead the prefetcher is looking, How many prefetches have been initiated but are not yet known to have completed, Process ID of the subscription worker process, OID of the relation that the worker is synchronizing; null for the main apply worker, Last write-ahead log location received, the initial value of this field being 0. IP address of the client connected to this WAL sender. A backend process wants to read a page into shared memory. Table28.31.pg_statio_all_sequences View, Number of disk blocks read from this sequence. Returns the time when this process was started. also pending an I/O operation, The ratio between the size of the shared buffer pool (defined by the shared_buffers parameter) and the This view will only contain information on standby servers, since conflicts do not occur on master servers. Waiting to access the list of finished serializable transactions. The pg_stat_all_tables view will contain one row for each table in the current database (including TOAST tables), showing statistics about accesses to that specific table.

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