Wait Events of Type Extension. Waiting to read or update old snapshot control information. Waiting to write a protocol message to a shared message queue. This is a feature, not a bug, because it allows you to perform several queries on the statistics and correlate the results without worrying that the numbers are changing underneath you. Choose the appropriate target Region. async: This standby server is asynchronous. 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_mapping: Waiting to associate a data block with a buffer in the buffer pool. The argument can be one of CommitTs, MultiXactMember, MultiXactOffset, Notify, Serial, Subtrans, or Xact to reset the counters for only that entry. 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. It can also count calls to user-defined functions and the total time spent in each one. pg_stat_reset_single_function_counters ( oid ) void. Returns the OID of the database this backend is connected to. Definition: lwlock.h:190. Waiting to read or update replication slot state. Prevent sudden database connection spikes by using a connection pool. The server process is idle. your workload peak time if you see LWLock:BufferIO coinciding with checksum_last_failure timestamp with time zone. Number of deadlocks detected in this database. wait_event will identify the type of lock awaited. Waiting for the group leader to clear the transaction ID at end of a parallel operation. 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. See, One row only, showing statistics about the WAL archiver process's activity. It also tracks the total number of rows in each table, and information about . These numbers do not act as stated above; instead they update continuously throughout the transaction. Waiting for a relation data file to be truncated. When using the statistics to monitor collected data, it is important to realize that the information does not update instantaneously. Waiting for the page number needed to continue a parallel B-tree scan to become available. pg_stat_get_backend_userid ( integer ) oid. Number of decoded transactions sent to the decoding output plugin for this slot. Waiting in WAL receiver to establish connection to remote server. Waiting for I/O on a clog (transaction status) buffer. wait_event will identify the specific wait point. This and other streaming counters for this slot can be used to tune logical_decoding_work_mem. Waiting to read or update vacuum-related information for a B-tree index. 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. The pg_stat_user_functions view will contain one row for each tracked function, showing statistics about executions of that function. Aurora PostgreSQL wait events PDF RSS The following table lists the wait events for Aurora PostgreSQL that most commonly indicate performance problems, and summarizes the most common causes and corrective actions. 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. Time when this process' current transaction was started, or null if no transaction is active. Extensions can add LWLock types to the list shown in Table28.12. wait_event will contain a name identifying the purpose of the lightweight lock. Waiting to acquire a speculative insertion lock. If this field is null, it indicates that this is an internal server process. Waiting to read or update information about synchronous replicas. Waiting for stats dynamic shared memory allocator access, Waiting for stats shared memory hash table access, Waiting for shared memory stats data access. A database-wide ANALYZE is recommended after the statistics have been reset. Waiting to manage space allocation in shared memory. Waiting for data to reach durable storage while assigning WAL sync method. Waiting to read or update the last value set for a transaction commit timestamp. The per-table and per-index functions take a table or index OID. Waiting in main loop of logical replication launcher process. Waiting for SLRU data to reach durable storage following a page write. PostgreSQL's cumulative statistics system supports collection and reporting of information about server activity. gorthx on Twitter See Table28.5 through Table28.13. pg_stat_get_backend_xact_start ( integer ) timestamp with time zone. The track_functions parameter controls exactly which functions are tracked. Waiting for a WAL file to reach durable storage. Waiting for a read from the control file. 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. Waiting to read or truncate multixact information. It works like this: Name of the user logged into this backend, Name of the application that is connected to this backend. Waiting for background worker to start up. The new locking scheme avoids grabbing system-wide exclusive locks in common code paths. Waiting for data to reach durable storage while adding a line to the data directory lock file. However, these statistics do not give the entire story: due to the way in which PostgreSQL handles disk I/O, data that is not in the PostgreSQL buffer cache might still reside in the kernel's I/O cache, and might therefore still be fetched without requiring a physical read. Alternatively, you can invoke pg_stat_clear_snapshot(), which will discard the current transaction's statistics snapshot (if any). Indexes can be used by simple index scans, bitmap index scans, and the optimizer. The LWLock that this article will introduce is a lightweight lock (Lightweight Lock) based on SpinLock. Waiting to read data from the client while establishing a GSSAPI session. For an asynchronous standby, the replay_lag column approximates the delay before recent transactions became visible to queries. The pg_stat_ssl view will contain one row per backend or WAL sender process, showing statistics about SSL usage on this connection. 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. Presently, the collector can count accesses to tables and indexes in both disk-block and individual-row terms. Waiting for an elected Parallel Hash participant to allocate the initial hash table. streaming: This WAL sender is streaming changes after its connected standby server has caught up with the primary. This field is truncated if the principal is longer than NAMEDATALEN (64 characters in a standard build). This is the only column in this view that returns a value reflecting current state; all other columns return the accumulated values since the last reset. Waiting for a relation data file to be extended. Returns the wait event type name if this backend is currently waiting, otherwise NULL. 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. Also, the collector itself emits a new report at most once per PGSTAT_STAT_INTERVAL milliseconds (500 ms unless altered while building the server). Waiting for a serialized historical catalog snapshot to reach durable storage. Lock: The backend is waiting for a heavyweight lock. Waiting to retrieve messages from the shared catalog invalidation queue. IPC: The server process is waiting for some activity from another process in the server. Waiting to associate a data block with a buffer in the buffer pool. 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 replication slot to become inactive so it can be dropped. PostgreSQL 's statistics collector is a subsystem that supports collection and reporting of information about server activity. See, One row for each tracked function, showing statistics about executions of that function. The pg_statio_ views are primarily useful to determine the effectiveness of the buffer cache. If a backend is in the active state, it may or may not be waiting on some event. Waiting for an elected Parallel Hash participant to allocate more batches. Waiting for the relation map file to reach durable storage. This has no effect in a quorum-based synchronous replication. postgres 26 Heap_Insert See, One row only, showing statistics about WAL activity. 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, Process ID of a backend or WAL sender process, Version of SSL in use, or NULL if SSL is not in use on this connection, Name of SSL cipher in use, or NULL if SSL is not in use on this connection, Number of bits in the encryption algorithm used, or NULL if SSL is not used on this connection, True if SSL compression is in use, false if not, or NULL if SSL is not in use on this connection, 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. Waiting in main loop of WAL writer process. Type of current backend. In order to write the disk block into buffer memory, the buffer cache's hash table entry needs updating. Client: The server process is waiting for some activity on a socket from user applications, and that the server expects something to happen that is independent from its internal processes. 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. Waiting to read or update dynamic shared memory allocation information. Waiting for activity from child process when executing. See, At least one row per subscription, showing information about the subscription workers. Text of this backend's most recent query. streaming: This WAL sender is streaming changes after its connected standby server has caught up with the primary. The total number of rows in each table, and information about vacuum and analyze actions for each table are also counted. Using pg_stat_reset() also resets counters that autovacuum uses to determine when to trigger a vacuum or an analyze. Since collection of statistics adds some overhead to query execution, the system can be configured to collect or not collect information. This lock is used to handle multiple sessions that all require access to the same Waiting for a write while creating the data directory lock file. 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. Waiting in main loop of WAL sender process. After v9.5, the buffer cache is protected by 128 hash tables each protected by a LWLock. The pg_stat_bgwriter view will always have a single row, containing global data for the cluster. 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. 214 . Waiting for a write to a relation data file. Table28.12.pg_stat_database_conflicts View. Waiting in main loop of background writer process. 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. 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. This is controlled by configuration parameters that are normally set in postgresql.conf. The LWLock:BufferIO wait event precedes the IO:DataFileRead wait event. Some of the information in the dynamic statistics views shown in Table28.1 is security restricted. Waiting to receive bytes from a shared message queue. If the argument is other (or indeed, any unrecognized name), then the counters for all other SLRU caches, such as extension-defined caches, are reset. Waiting for I/O on a multixact offset SLRU buffer. Re: Improve WALRead() to suck data directly from WAL buffers when possible - Mailing list pgsql-hackers See. pg_stat_get_backend_wait_event ( integer ) text. disabled: This state is reported if track_activities is disabled in this backend. Waiting for a read when creating a new WAL segment by copying an existing one. Time when this process was started. Waiting to access a shared TID bitmap during a parallel bitmap index scan. Waiting for a write when creating a new WAL segment by copying an existing one. The parameter track_io_timing enables monitoring of block read and write times. Waiting for a replication slot control file to reach durable storage while restoring it to memory. See, One row per subscription, showing statistics about errors. This view will only contain information on standby servers, since conflicts do not occur on master servers. LWLock: The backend is waiting for a lightweight lock. The lag times reported in the pg_stat_replication view are measurements of the time taken for recent WAL to be written, flushed and replayed and for the sender to know about it. a page) has to be retrieved outside the shared buffer pool. A transaction can also see its own statistics (not yet flushed out to the shared memory statistics) in the views pg_stat_xact_all_tables, pg_stat_xact_sys_tables, pg_stat_xact_user_tables, and pg_stat_xact_user_functions. Waiting to read or update shared multixact state. Waiting for a logical replication remote server to send data for initial table synchronization. It is used per the rules above. Only directly connected standbys are listed; no information is available about downstream standby servers. 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. When the server shuts down cleanly, a permanent copy of the statistics data is stored in the pg_stat subdirectory, so that statistics can be retained across server restarts. The pg_stat_user_functions view will contain one row for each tracked function, showing statistics about executions of that function. PostgreSQL 15.2, 14.7, 13.10, 12.14, and 11.19 Released, 28.2.1. Waiting during base backup when throttling activity. Waiting to acquire a speculative insertion lock. Alone the requirement of separate fsyncs and everything is pretty bothersome. * 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). This should not be used for data integrity checks. Waiting for a write while initializing a new WAL file. Waiting for SSL while attempting connection. Waiting to read or update transaction commit timestamps. See, One row for each sequence in the current database, showing statistics about I/O on that specific sequence. 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 read of a serialized historical catalog snapshot. If this field is null, it indicates that the client is connected via a Unix socket on the server machine. Waiting for other Parallel Hash participants to finish inserting tuples into new buckets. 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 to read or update the progress of one replication origin. Waiting for changes to a relation data file to reach durable storage. Logical decoding plugins may optionally emit tracking messages; if they do not, the tracking mechanism will simply display NULL lag. Waiting for a write to a replication slot control file. PostgreSQL utilizes lightweight locks (LWLocks) to synchronize and control access to the buffer content. This effect can mean that you have a small shared buffers setting. 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. Waiting for a read during recheck of the data directory lock file. Identifier of this backend's most recent query. Doing this helps The combination of certificate serial number and certificate issuer uniquely identifies a certificate (unless the issuer erroneously reuses serial numbers). Waiting for a write to the relation map file. Additional functions related to statistics collection are listed in Table28.19. This is used by system processes waiting for activity in their main processing loop. your experience with the particular feature or requires further clarification, 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. 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). Possible values are: active: The backend is executing a query. Waiting to read or update the last value set for the transaction timestamp. Waiting for an asynchronous prefetch from a relation data file. However, current-query information collected by track_activities is always up-to-date. fastpath function call: The backend is executing a fast-path function. These access functions use a backend ID number, which ranges from one to the number of currently active backends. IP address of the client connected to this backend. For tranches registered by extensions, the name is specified by extension and this will be displayed as wait_event. backup: This WAL sender is sending a backup. See, One row per connection (regular and replication), showing information about SSL used on this connection. Waiting to allocate or free a replication slot. Waiting for a write of a two phase state file. Number of in-progress transactions streamed to the decoding output plugin after the memory used by logical decoding to decode changes from WAL for this slot has exceeded logical_decoding_work_mem. Waiting in main loop of logical apply process. The counter gets incremented for both top-level transactions and subtransactions. Waiting for I/O on a serializable transaction conflict SLRU buffer. So the statistics will show static information as long as you continue the current transaction. Waiting for an elected Parallel Hash participant to allocate a hash table. , LWTRANCHE_MXACTMEMBER_BUFFERS, LWTRANCHE_ASYNC_BUFFERS, LWTRANCHE_OLDSERXID_BUFFERS, LWTRANCHE_WAL_INSERT, LWTRANCHE_BUFFER_CONTENT, LWTRANCHE_BUFFER_IO_IN_PROGRESS, LWTRANCHE . The buffer_tag comprises three values: the RelFileNode and the fork number of the relation to which its page belongs, and the block number of its page. Waiting to select the starting location of a synchronized table scan. This is controlled by configuration parameters that are normally set in postgresql.conf. Waiting to retrieve or store information about serializable transactions. Returns the time when the backend's current transaction was started. 105 #define BUFFER_MAPPING_LWLOCK_OFFSET NUM_INDIVIDUAL_LWLOCKS. A backend process wants to read a page into shared memory. Per-Backend Statistics Functions, Copyright 1996-2023 The PostgreSQL Global Development Group. Waiting for a write of a timeline history file received via streaming replication. Waiting for truncate of mapping data during a logical rewrite. Waiting for logical replication remote server to send data for initial table synchronization. The pg_stat_database view will contain one row for each database in the cluster, showing database-wide statistics. Waiting for a read of a serialized historical catalog snapshot. Timeout: The server process is waiting for a timeout to expire. 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. 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 read or update the fast-path lock information. Waiting to elect a Parallel Hash participant to allocate the initial hash table. Waiting to elect a Parallel Hash participant to allocate more batches. pg_stat_get_activity ( integer ) setof record. The wait_event and state columns are independent. There are also several other views, listed in Table28.2, available to show the accumulated statistics. See, One row for each table in the current database, showing statistics about I/O on that specific table. (See Chapter20 for details about setting configuration parameters.). Waiting for I/O on a transaction status SLRU buffer. Waiting to access the list of predicate locks held by serializable transactions. The following wait events are a subset of the list in Amazon Aurora PostgreSQL wait events. Returns the text of this backend's most recent query. Waiting for I/O on a commit timestamp SLRU buffer. A process acquires an LWLock in a shared mode to read from the buffer and an exclusive mode to write to the buffer. Waiting to read or update the current state of autovacuum workers. Sometimes it may be more convenient to obtain just a subset of this information. I am not the DBA, but receive reports occasionally when an application is causing load on the system. Waiting to access the list of finished serializable transactions. replication_slot_io: Waiting for I/O on a replication slot. In addition, background workers registered by extensions may have additional types. Connection string used by this WAL receiver, with security-sensitive fields obfuscated. pg_stat_get_backend_activity ( integer ) text. Additional Statistics Functions. The generated IO patterns are also much worse. Normally these parameters are set in postgresql.conf so that they apply to all server processes, but it is possible to turn them on or off in individual sessions using the SET command. Waiting while sending synchronization requests to the checkpointer, because the request queue is full. Waiting in main loop of the archiver process. Table28.17.pg_statio_all_sequences View. Waiting for a write of a timeline history file received via streaming replication. The access functions for per-database statistics take a database OID as an argument to identify which database to report on. Waiting to ensure that the table it has selected for a vacuum still needs vacuuming. Waiting to access the commit timestamp SLRU cache. Every PostgreSQL process collects statistics locally, then updates the shared data at appropriate intervals. Waiting for confirmation from a remote server during synchronous replication. Text of this backend's most recent query. The optimizer also accesses indexes to check for supplied constants whose values are outside the recorded range of the optimizer statistics because the optimizer statistics might be stale. Process ID of a backend or WAL sender process, Version of SSL in use, or NULL if SSL is not in use on this connection, Name of SSL cipher in use, or NULL if SSL is not in use on this connection, Number of bits in the encryption algorithm used, or NULL if SSL is not used on this connection. Normally these parameters are set in postgresql.conf so that they apply to all server processes, but it is possible to turn them on or off in individual sessions using the SET command. 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. Waiting for a replication slot control file to reach durable storage. BufferCacheHitRatio metric dips. The function pg_stat_get_backend_idset provides a convenient way to generate one row for each active backend for invoking these functions. Time at which these statistics were last reset. Returns the IP address of the client connected to this backend. Waiting for a write of mapping data during a logical rewrite. being read from storage. Waiting to access the serializable transaction conflict SLRU cache. Then identify which query Waiting to access a shared tuple store during parallel query. The idx_tup_read and idx_tup_fetch counts can be different even without any use of bitmap scans, because idx_tup_read counts index entries retrieved from the index while idx_tup_fetch counts live rows fetched from the table. See, One row per database, showing database-wide statistics. But processes can also await other events: Waits for input/output ( IO) occur when a process needs to read or write data. The pg_stat_activity view will have one row per server process, showing information related to the current activity of that process. Number of backends currently connected to this database, or NULL for shared objects. Please refer to your browser's Help pages for instructions. This field will only be non-null for IP connections, and only when log_hostname is enabled. sync: This standby server is synchronous. My application is using Postgres as DBMS, the version of Postgres that i'm using is 10.3 with the extension Postgis installed. Table28.15.pg_stat_replication_slots View, A unique, cluster-wide identifier for the replication slot. Waiting to read or truncate multixact information. Waiting for a read of the relation map file. Waiting to read or update information about the state of synchronous replication. Waiting for another process to be attached to a shared message queue. This can be used to gauge the delay that synchronous_commit level on incurred while committing if this server was configured as a synchronous standby.