Some of the information in the dynamic statistics views shown in Table28.1 is security restricted. For example, to show the PIDs and current queries of all backends: Table28.35. However, they are also used to ensure mutual exclusion for certain internal operations such as relation extension. The function pg_stat_get_backend_idset provides a convenient way to generate one row for each active backend for invoking these functions. Waiting to manage an extension's space allocation in shared memory. Waiting to read or update information about. The WALWriteLock wait occurs while PostgreSQL flushes WAL records to disk or during a WAL segment switch.. How to reduce this wait . Waiting to update limits on transaction id and multixact consumption. Waiting for I/O on a clog (transaction status) buffer. See, One row per connection (regular and replication), showing information about GSSAPI authentication and encryption used on this connection. 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. The type of event for which the backend is waiting, if any; otherwise NULL. This category is useful for modules to track custom waiting points. Waiting to associate a data block with a buffer in the buffer pool. PostgreSQL's cumulative statistics system supports collection and reporting of information about server activity. This is consistent with the goal of measuring synchronous commit and transaction visibility delays for recent write transactions. TCP port number that the client is using for communication with this backend, or -1 if a Unix socket is used. The IO:DataFileRead wait event occurs while data is (The path case can be distinguished because it will always be an absolute path, beginning with /.). For an asynchronous standby, the replay_lag column approximates the delay before recent transactions became visible to queries. Waiting in main loop of background writer process background worker. Waiting for a write to the relation map file. In rows about other sessions, many columns will be null. See, One row per replication slot, showing statistics about the replication slot's usage. Waiting for logical rewrite mappings to reach durable storage. This can be used to gauge the delay that. Number of decoded transactions sent to the decoding output plugin for this slot. The generated IO patterns are also much worse. Waiting in background writer process, hibernating. Waiting for a two phase state file to reach durable storage. 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. finish their input/output (I/O) operations when concurrently trying to access a page. Waiting for data to reach durable storage while assigning a new WAL sync method. Time elapsed between flushing recent WAL locally and receiving notification that this standby server has written, flushed and applied it. See, One row only, showing statistics about the background writer process's activity. Waiting to read or write a data page in memory. This effect can mean that you have a small shared buffers setting. Waiting to insert WAL into a memory buffer. Waiting for changes to a relation data file to reach durable storage. 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. Waiting for I/O on a transaction status SLRU buffer. Send time of last reply message received from standby server. Synchronous state of this standby server. Waiting for a replication slot control file to reach durable storage while restoring it to memory. Waiting to access the list of finished serializable transactions. 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. So the displayed information lags behind actual activity. Several predefined views, listed in Table28.1, are available to show the current state of the system. 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. Waiting to read or update multixact member mappings. PostgreSQL utilizes lightweight locks (LWLocks) to synchronize and control access to the buffer content. This wait event information is relevant for all Aurora PostgreSQL 13 versions. Waiting to read or update the replication progress. Waiting for an update to the control file to reach durable storage. This counter is incremented each time a transaction is streamed, and the same transaction may be streamed multiple times. Waiting to read data from the client while establishing a GSSAPI session. Waiting for parallel bitmap scan to become initialized. It can also count calls to user-defined functions and the total time spent in each one. Waiting for the group leader to clear the transaction ID at end of a parallel operation. Waiting in main loop of logical replication apply process. The server process is idle. Waiting to write a protocol message to a shared message queue. Streaming only works with top-level transactions (subtransactions can't be streamed independently), so the counter is not incremented for subtransactions. Current WAL sender state. 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. Waiting to write zero bytes to a dynamic shared memory backing file. Provide feedback Waiting for a relation data file to be truncated. Time when this process was started. Waiting for a two phase state file to reach durable storage. 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 for a relation data file to be extended. Thanks for letting us know we're doing a good job! Waiting to replace a page in WAL buffers. Cumulative statistics are collected in shared memory. Number of times in-progress transactions were streamed to the decoding output plugin while decoding changes from WAL for this slot. The statistics collector transmits the collected information to other PostgreSQL processes through temporary files. Waiting to read or update dynamic shared memory allocation information. Waiting for confirmation from a remote server during synchronous replication. wait_event will identify the specific wait point. Please refer to your browser's Help pages for instructions. 39919 LWLock buffer_mapping 5119 Client ClientRead 3116 IO DataFileRead With C-Hash Event Count Event Type Event Name The per-table and per-index functions take a table or index OID. Waiting for a write to a relation data file. It is quite possible that user has registered the tranche in one of the backends (by having allocation in dynamic shared memory) in which case other backends won't have that information, so we display extension for such cases. Waiting to read or update the fast-path lock information. Waiting to access the list of predicate locks held by serializable transactions. Waiting for the version file to be written while creating a database. A backend process wants to read a page into shared memory. The pg_stat_all_indexes view will contain one row for each index in the current database, showing statistics about accesses to that specific index. The next use of statistical information will cause a new snapshot to be fetched. Waiting in main loop of logical apply process. Re: Improve WALRead() to suck data directly from WAL buffers when possible Waiting for a read from a replication slot control file. However, current-query information collected by track_activities is always up-to-date. The pg_stat_bgwriter view will always have a single row, containing global data for the cluster. The pg_stat_activity view will have one row per server process, showing information related to the current activity of that process. disabled: This state is reported if track_activities is disabled in this backend. The access functions for per-database statistics take a database OID as an argument to identify which database to report on. See, One row only, showing statistics about WAL activity. 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. 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. For more information, see LWLock:buffer_mapping. 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. 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.

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