The pg_stat_archiver view will always have a single row, containing data about the archiver process of the cluster. See, One row per connection (regular and replication), showing information about SSL used on this connection. Only directly connected standbys are listed; no information is available about downstream standby servers. See, One row for each backend (including autovacuum worker processes) running, One row only, showing statistics about the WAL archiver process's activity. Waiting for parallel bitmap scan to become initialized. Waiting to allocate or free a replication slot. Waiting for a write when creating a new WAL segment by copying an existing one. See Table28.4 for details. Waiting for activity from child process when executing. However, they are also used to ensure mutual exclusion for certain internal operations such as relation extension. Waiting to ensure that a table selected for autovacuum still needs vacuuming. It can also count calls to user-defined functions and the total time spent in each one. Waiting in main loop of syslogger process. Each shared buffer has an I/O lock that is associated with the LWLock:BufferIO wait event, each time a block (or Waiting for a relation data file to be truncated. Waiting in main loop of WAL sender process. pg_stat_get_backend_pid ( integer ) integer, pg_stat_get_backend_start ( integer ) timestamp with time zone. Note that this includes the transactions that are streamed and/or spilled. 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. My application is using Postgres as DBMS, the version of Postgres that i'm using is 10.3 with the extension Postgis installed. Waiting for a write of a serialized historical catalog snapshot. The track_functions parameter controls exactly which functions are tracked. Waiting in background writer process, hibernating. See, Time when the current transaction was started. Waiting for background worker to shut down. Waiting for a write during reorder buffer management. BufferPin: The server process is waiting to access to a data buffer during a period when no other process can be examining that buffer. Waiting while sending synchronization requests to the checkpointer, because the request queue is full. (The path case can be distinguished because it will always be an absolute path, beginning with /.). backup: This WAL sender is sending a backup. Postgres Locking: When is it Concerning? The pg_stat_bgwriter view will always have a single row, containing global data for the cluster. 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 to add or examine predicate lock information. Waiting to manage space allocation in shared memory. Time elapsed between flushing recent WAL locally and receiving notification that this standby server has written, flushed and applied it. your experience with the particular feature or requires further clarification, These access functions use a backend ID number, which ranges from one to the number of currently active backends. your workload peak time if you see LWLock:BufferIO coinciding with Waiting for a write of a two phase state file. Waiting for data to reach durable storage while creating the data directory lock file. Monitoring systems should choose whether to represent this as missing data, zero or continue to display the last known value. For an asynchronous standby, the replay_lag column approximates the delay before recent transactions became visible to queries. 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. If state is active this field shows the currently executing query. Waiting to add a message in shared invalidation queue. The access functions for per-database statistics take a database OID as an argument to identify which database to report on. Re: Improve WALRead() to suck data directly from WAL buffers when possible quorum: This standby server is considered as a candidate for quorum standbys. Each individual server process transmits new statistical counts to the collector just before going idle; so a query or transaction still in progress does not affect the displayed totals. Returns the wait event name if this backend is currently waiting, otherwise NULL. Time when this process was started. Waiting to read or update the last value set for the transaction timestamp. Waiting to access a shared TID bitmap during a parallel bitmap index scan. This category is useful for modules to track custom waiting points. Waiting for I/O on a commit timestamp SLRU buffer. See, One row per database, showing database-wide statistics about query cancels due to conflict with recovery on standby servers. Total amount of time spent syncing WAL files to disk via issue_xlog_fsync request, in milliseconds (if track_wal_io_timing is enabled, fsync is on, and wal_sync_method is either fdatasync, fsync or fsync_writethrough, otherwise zero). 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 the group leader to clear the transaction ID at end of a parallel operation. The pg_stat_slru view will contain one row for each tracked SLRU cache, showing statistics about access to cached pages. Thanks for letting us know this page needs work. Waiting for a read of a two phase state file. See. Waiting to retrieve or remove messages from shared invalidation queue. Waiting for confirmation from a remote server during synchronous replication. Waiting for the relation map file to reach durable storage. A backend process wants to read a page into shared memory. See, Only one row, showing statistics about blocks prefetched during recovery. 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. For client backends, this is the time the client connected to the server. Waiting in main loop of background writer process. Waiting for WAL from a stream at recovery. Waiting for SLRU data to reach durable storage following a page write. Streaming only works with top-level transactions (subtransactions can't be streamed independently), so the counter is not incremented for subtransactions. Waiting for I/O on a multixact member SLRU buffer. - a BufFreeList LWLock was getting acquired to find a free buffer for a page - to change the association of buffer in buffer mapping hash table a LWLock is acquired on a hash partition to which the buffer to be associated belongs and as there were just 16 such partitions, there was huge contention when multiple clients Waiting for the group leader to update transaction status at end of a parallel operation. Waiting for WAL buffers to be written to disk. If this field is null, it indicates that this is an internal server process. Waiting for logical rewrite mappings to reach durable storage. 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. Lag times work automatically for physical replication. Number of decoded transactions sent to the decoding output plugin for this slot. Returns the time when the backend's current transaction was started. Waiting to perform an operation on a list of locks held by serializable transactions. Waiting for a newly initialized WAL file to reach durable storage. Waiting to acquire an exclusive lock to truncate off any empty pages at the end of a table vacuumed. Resets statistics for a single table or index in the current database or shared across all databases in the cluster to zero. disabled: This state is reported if track_activities is disabled in this backend. proc: Waiting to read or update the fast-path lock information. The parameter track_counts controls whether statistics are collected about table and index accesses. 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. 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. 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. 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. See Table28.5 through Table28.13. The pg_stat_recovery_prefetch view will contain only one row. Several predefined views, listed in Table28.1, are available to show the current state of the system. Its See, Only one row, showing statistics about the WAL receiver from that receiver's connected server. Waiting to read or update multixact member mappings. See, One row for each index in the current database, showing statistics about I/O on that specific index. Its purpose is for the same page to be read into the shared buffer. Waiting to replace a page in WAL buffers. Waiting to send bytes to a shared message queue. 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. BK_1935: "IObuffer_locks,ControlLock()"IOControlLockControlLockIOSlruSharedData. When using the statistics to monitor collected data, it is important to realize that the information does not update instantaneously. Waiting for parallel workers to finish computing. Waiting to insert WAL into a memory buffer. There are also several other views, listed in Table28.2, available to show the accumulated statistics. 213 * Prior to PostgreSQL 9.4, we used an enum type called LWLockId to refer. Waiting for parallel bitmap scan to become initialized. This can be used to gauge the delay that. Waiting in WAL receiver to receive data from remote server. In addition, background workers registered by extensions may have additional types. Waiting to access the list of finished serializable transactions. Waiting to apply WAL during recovery because of a delay setting. IP address of the client connected to this WAL sender. 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. Waiting for WAL files required for a backup to be successfully archived. wait_event will identify the specific wait point. Waiting for confirmation from remote server during synchronous replication. Waiting for data to reach durable storage while adding a line to the data directory lock file. (Conflicts occur only on standby servers; see, Number of temporary files created by queries in this database. Waiting for a read from a replication slot control file. Waiting to access the list of finished serializable transactions. This wait event information is relevant for all Aurora PostgreSQL 13 versions. 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. LWLock- buffer_mapping. Statistics Collection Configuration, One row per server process, showing information related to the current activity of that process, such as state and current query. Waiting to access the list of predicate locks held by the current serializable transaction during a parallel query. This and other spill counters can be used to gauge the I/O which occurred during logical decoding and allow tuning logical_decoding_work_mem. Waiting in background writer process, hibernating. Synchronous state of this standby server. Waiting for a write of a newly created timeline history file. The server process is waiting for a lightweight lock. Time when this process was started. Waiting to read or update information about synchronous replicas. fastpath function call: The backend is executing a fast-path function. Waiting for WAL to be flushed in WAL sender process. 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. Waiting in main loop of WAL sender process. ), 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 read or update old snapshot control information. Waiting to read or update the state of prepared transactions. Waiting to read while creating the data directory lock file. 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. The server process is waiting for a heavyweight lock. For client backends, this is the time the client connected to the server. Use partitioned tables (which also have partitioned indexes). Number of data page checksum failures detected in this database (or on a shared object), or NULL if data checksums are not enabled. Since collection of statistics adds some overhead to query execution, the system can be configured to collect or not collect information. PostgreSQL 15.2, 14.7, 13.10, 12.14, and 11.19 Released, 28.2.1. The server process is waiting for an I/O operation to complete. The server process is waiting for some condition defined by an extension module.