Only directly connected standbys are listed; no information is available about downstream standby servers. Avoid PostgreSQL LWLock:buffer_content locks in Amazon Aurora: Tips and Amount of decoded transaction data spilled to disk while performing decoding of changes from WAL for this slot. Since collection of statistics adds some overhead to query execution, the system can be configured to collect or not collect information. Verify whether you have unused indexes, then remove them. Waiting in main loop of WAL sender process. Resets statistics for a single subscription shown in the pg_stat_subscription_stats view to zero. (To prevent ordinary users from hiding their activity from the administrator, only superusers are allowed to change these parameters with SET.). Possible types are autovacuum launcher, autovacuum worker, logical replication launcher, logical replication worker, parallel worker, background writer, client backend, checkpointer, archiver, startup, walreceiver, walsender and walwriter. Waiting for WAL files required for a backup to be successfully archived. 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. This field is truncated if the principal is longer than NAMEDATALEN (64 characters in a standard build). Last write-ahead log location already received and written to disk, but not flushed. The wait_event and state columns are independent. wait_event will identify the specific wait point. This wait event information is relevant for all Aurora PostgreSQL 13 versions. Waiting in main loop of WAL receiver process. It also tracks the total number of rows in each table, and information about vacuum and analyze actions for each table. After v9.5, the buffer cache is protected by 128 hash tables each protected by a LWLock. However, they are also used to ensure mutual exclusion for certain internal operations such as relation extension. This category is useful for modules to track custom waiting points. Time elapsed between flushing recent WAL locally and receiving notification that this standby server has written and flushed it (but not yet applied it). ), 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). 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. There are also several other views, listed in Table28.2, available to show the results of statistics collection. Use partitioned tables (which also have partitioned indexes). In all other states, it shows the last query that was executed. Waiting to manage space allocation in shared memory. potential: This standby server is now asynchronous, but can potentially become synchronous if one of current synchronous ones fails. Java_Java_File_Io_Buffer - Alternatively, one can build custom views using the underlying cumulative statistics functions, as discussed in Section28.2.24. buffer_io: Waiting for I/O on a data page. Waiting for other process to be attached in shared message queue. See Table28.4 for details. Waiting to add a message in shared invalidation queue. The buffer_mapping LWLock wait event will be . In a bitmap scan the output of several indexes can be combined via AND or OR rules, so it is difficult to associate individual heap row fetches with specific indexes when a bitmap scan is used. Waiting to perform an operation on a list of locks held by serializable transactions. 28.2. The Cumulative Statistics System - PostgreSQL Documentation A backend process is waiting to associate a data block with a buffer in the shared buffer pool. Waiting to acquire a lock on a non-relation database object. Waiting in main loop of logical replication apply process. idle in transaction: The backend is in a transaction, but is not currently executing a query. For tranches registered by extensions, the name is specified by extension and this will be displayed as wait_event. See, One row for each sequence in the current database, showing statistics about I/O on that specific sequence. The server process is waiting for a lightweight lock. 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 to get a snapshot or clearing a transaction id at transaction end. Waiting for a two phase state file to reach durable storage. TCP port number that the client is using for communication with this WAL sender, or -1 if a Unix socket is used, Time when this process was started, i.e., when the client connected to this WAL sender. postgres/README at master postgres/postgres GitHub Waiting to read or update replication slot state. Waiting for a write of logical rewrite mappings. The full object locks which last (usually) for the duration of a transaction and which you can see in pg_locks have info about them stored in shared memory. proc: Waiting to read or update the fast-path lock information. Waiting for SLRU data to reach durable storage during a checkpoint or database shutdown. See, One row only, showing statistics about the WAL archiver process's activity. Note that this includes data that is streamed and/or spilled. Waiting for data to reach durable storage while assigning WAL sync method. In all other states, it shows the identifier of last query that was executed. ru> Date: 2015-11-19 14:04:28 Message-ID: 20151119170428.490de41d lp [Download RAW message or body] Thank you for the review. pg_stat_get_backend_pid ( integer ) integer, pg_stat_get_backend_start ( integer ) timestamp with time zone. Waiting for a write of a timeline history file received via streaming replication. If this field is null, it indicates that the client is connected via a Unix socket on the server machine. Resets some cluster-wide statistics counters to zero, depending on the argument. Waiting to update limits on transaction id and multixact consumption. Waiting for a serialized historical catalog snapshot to reach durable storage. Waiting in main loop of archiver process. Waiting for the termination of another backend. Identifier of this backend's most recent query. Waiting for a two phase state file to reach durable storage. Waiting for WAL to reach durable storage during bootstrapping. pg_stat_get_backend_activity ( integer ) text. If a backend is in the active state, it may or may not be waiting on some event. backup: This WAL sender is sending a backup. For an asynchronous standby, the replay_lag column approximates the delay before recent transactions became visible to queries. For example, to show the PIDs and current queries of all backends: Table28.35. This is consistent with the goal of measuring synchronous commit and transaction visibility delays for recent write transactions. This event type indicates a process waiting for activity in its main processing loop. Text of this backend's most recent query. Waiting for a write while creating the data directory lock file. 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. The fields returned are a subset of those in the pg_stat_activity view. Waiting for a newly initialized WAL file to reach durable storage. Waiting for SLRU data to reach durable storage during a checkpoint or database shutdown. 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. Current overall state of this backend. wait_event will identify the specific wait point. Waiting in main loop of autovacuum launcher process. Avoid PostgreSQL LWLock:buffer_content locks in Amazon Aurora: Tips and Activity status of the WAL receiver process, First write-ahead log location used when WAL receiver is started, First timeline number used when WAL receiver is started. Waiting for a read during a file copy operation. Waiting for a write to the relation map file. pg_stat_get_backend_client_port ( integer ) integer. 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. 5mins of Postgres E25: Postgres lock monitoring, LWLocks and the log Waiting for data to reach durable storage while creating the data directory lock file. Waiting for base backup to read from a file. If you've got a moment, please tell us how we can make the documentation better. In order to write the disk block into buffer memory, the buffer cache's hash table entry needs updating. Note, however, that the existence of a session and its general properties such as its sessions user and database are visible to all users. Principal used to authenticate this connection, or NULL if GSSAPI was not used to authenticate this connection. 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. IP address of the client connected to this backend. Waiting for background worker to shut down. The parameter track_counts controls whether cumulative statistics are collected about table and index accesses. query performance - PostgreSQL LWLock: lock_manager issue - Database Waiting to read or update the state of prepared transactions. Waiting to synchronize workers during Parallel Hash Join plan execution. See, One row for each table in the current database, showing statistics about accesses to that specific table. You can split your Waiting for a read when creating a new WAL segment by copying an existing one. number of buffers needed by the current workload, The size of the shared buffer pool not being well balanced with the number of pages being evicted by other Waiting between writes while performing a checkpoint. Priority of this standby server for being chosen as the synchronous standby in a priority-based synchronous replication. Waiting for a write of logical rewrite mappings. 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 for WAL to reach durable storage during bootstrapping. 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 some interaction with another server process. IPC: The server process is waiting for some activity from another process in the server. Returns the process ID of the server process attached to the current session. The server process is waiting for activity on a socket connected to a user application. Simple test for lock_waits log messages. Topics Relevant engine versions Context Causes Actions Relevant engine versions Waiting to read or update multixact offset mappings. This is used by system processes waiting for activity in their main processing loop. LWLock:BufferIO. In such cases, an older set of per-backend statistics access functions can be used; these are shown in Table28.20. The pg_stat_activity view will have one row per server process, showing information related to the current activity of that process. (See Chapter19 for details about setting configuration parameters.). Waiting in main loop of startup process for WAL to arrive, during streaming recovery. Resets statistics for a single function in the current database to zero. The track_functions parameter controls exactly which functions are tracked. Waiting to read or update shared multixact state. 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. sync: This standby server is synchronous. Waiting for the group leader to clear the transaction ID at end of a parallel operation. Number of backends currently connected to this database. See, One row only, showing statistics about the background writer process's activity. Waiting for a replication origin to become inactive to be dropped. BufferCacheHitRatio and LWLock:BufferIO wait Waiting for a relation data file to reach durable storage. Type of current backend. ; Ensure that filesystem journaling is turned off for data files and WAL files. Returns the IP address of the client connected to this backend. 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. 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). Waiting for startup process to send initial data for streaming replication. When analyzing statistics interactively, or with expensive queries, the time delta between accesses to individual statistics can lead to significant skew in the cached statistics. Resetting these counters can cause autovacuum to not perform necessary work, which can cause problems such as table bloat or out-dated table statistics.