events. Tune max_wal_size and checkpoint_timeout based on PostgreSQL Entangled in Locks: Attempts to free it - Amit Kapila - Dilip Kumar PGCon 2017 . See, One row only, showing statistics about the WAL archiver process's activity. proc: Waiting to read or update the fast-path lock information. The management of the buffers in PostgreSQL consists of a buffer descriptor that contains metadata about the buffer and the buffer content that is read from the disk. The LWLock:BufferIO wait event precedes the IO:DataFileRead wait event. disabled: This state is reported if track_activities is disabled in this backend. Waiting for a read of a serialized historical catalog snapshot. Extension: The server process is waiting for activity in an extension module. Waiting in main loop of WAL receiver process. Extensions can add LWLock types to the list shown in Table28.12. Resets statistics for a single subscription shown in the pg_stat_subscription_stats view to zero. . 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. Using pg_stat_reset() also resets counters that autovacuum uses to determine when to trigger a vacuum or an analyze. 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. Note that only tables, indexes, and functions in the current database can be seen with these functions. Lag times work automatically for physical replication. Waiting for a write when creating a new WAL segment by copying an existing one. 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. 28.2. The Cumulative Statistics System - PostgreSQL Documentation Table28.15.pg_stat_replication_slots View, A unique, cluster-wide identifier for the replication slot. 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. ), 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 for changes to a relation data file to reach durable storage. Waiting in main loop of archiver process. 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. pg_stat_get_backend_dbid ( integer ) oid. The track_functions parameter controls exactly which functions are tracked. Waiting to associate a data block with a buffer in the buffer pool. 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. Possible values are: Wait event name if backend is currently waiting, otherwise NULL. The parameter track_activities enables monitoring of the current command being executed by any server process. Waiting to read or update the progress of one replication origin. This field is truncated like client_dn. Waiting in WAL receiver to receive data from remote server. Waiting for other process to be attached in shared message queue. 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). Waiting for a replication slot control file to reach durable storage while restoring it to memory. The pg_statio_all_sequences view will contain one row for each sequence in the current database, showing statistics about I/O on that specific sequence. A snapshot is taken the first time cumulative statistics are accessed in a transaction if stats_fetch_consistency is set to snapshot. If this field is null, it indicates that the client is connected via a Unix socket on the server machine. Waiting for a write of a WAL page during bootstrapping. 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 for activity from a child process while executing a. Waiting for a read during a file copy operation. Waiting for a replication slot control file to reach durable storage while restoring it to memory. Presently, the collector can count accesses to tables and indexes in both disk-block and individual-row terms. Waiting to elect a Parallel Hash participant to allocate the initial hash table. The generated IO patterns are also much worse. (For example, in psql you could issue \d+ pg_stat_activity.) Time when this process' current transaction was started, or null if no transaction is active. See, One row per replication slot, showing statistics about the replication slot's usage. The pg_stat_user_functions view will contain one row for each tracked function, showing statistics about executions of that function. 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 in a cost-based vacuum delay point. The server process is waiting for an I/O operation to complete. Waiting for parallel query dynamic shared memory allocation lock. These access functions use a backend ID number, which ranges from one to the number of currently active backends. 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. 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. This block has to be read from outside the shared buffer pool, defined by the See Section30.5 for more information about the internal WAL function issue_xlog_fsync. This has no effect in a quorum-based synchronous replication. this form Text of this backend's most recent query. This is controlled by configuration parameters that are normally set in postgresql.conf. 28.2.3. For example, to show the PIDs and current queries of all backends: Table28.35. 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 parameter track_wal_io_timing enables monitoring of WAL write times. Waiting in main loop of syslogger process. Waiting to ensure that the table it has selected for a vacuum still needs vacuuming. also pending an I/O operation, The ratio between the size of the shared buffer pool (defined by the shared_buffers parameter) and the streaming: This WAL sender is streaming changes after its connected standby server has caught up with the primary. WALWriteLock | DBmarlin Docs and Knowledge Base PostgreSQL: Documentation: 11: 28.2. The Statistics Collector Waiting during base backup when throttling activity. to keep index reordering low and reduces its impact. Aurora PostgreSQL wait events - Amazon Aurora Time at which the last data page checksum failure was detected in this database (or on a shared object), or NULL if data checksums are not enabled. 'Re: [HACKERS] [PATCH] Refactoring of LWLock tranches' - MARC Waiting to add or examine locks for backends, or waiting to join or exit a locking group (used by parallel query). Waiting in main loop of WAL sender process. These numbers do not act as stated above; instead they update continuously throughout the transaction. 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. 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. pg_blocking_pids function. The WALWriteLock wait occurs while PostgreSQL flushes WAL records to disk or during a WAL segment switch.. How to reduce this wait . Returns the time when this process was started. The access functions for per-database statistics take a database OID as an argument to identify which database to report on. The buffer_mapping LWLock wait event will be . Type of current backend. Waiting to read or update background worker state. pg_stat_get_activity, the underlying function of the pg_stat_activity view, returns a set of records containing all the available information about each backend process. See, Only one row, showing statistics about the WAL receiver from that receiver's connected server. Logical decoding plugins may optionally emit tracking messages; if they do not, the tracking mechanism will simply display NULL lag. Waiting for a read of a two phase state file. 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. Waiting to elect a Parallel Hash participant to allocate more buckets. Current overall state of this backend. Time when this process' current transaction was started, or null if no transaction is active. This should not be used for data integrity checks. Time at which these statistics were last reset. Waiting to read or update shared notification state. IP address of the client connected to this backend. (Some locks have specific names; others are part of a group of locks each with a similar purpose.). The parameter track_io_timing enables monitoring of block read and write times. ru> Date: 2015-11-19 14:04:28 Message-ID: 20151119170428.490de41d lp [Download RAW message or body] Thank you for the review. Synchronous state of this standby server. 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. Number of times this function has been called, Total time spent in this function and all other functions called by it, in milliseconds, Total time spent in this function itself, not including other functions called by it, in milliseconds. The parameter track_functions enables tracking of usage of user-defined functions. Waiting for other Parallel Hash participants to finish inserting tuples into new buckets. Returns the time when the backend's most recent query was started. block. Javascript is disabled or is unavailable in your browser. PostgreSQL utilizes lightweight locks (LWLocks) to synchronize and control access to the buffer content. > However, someone with deeper knowledge of page pinning and buffer manager > internals could certainly devise a better solution. The pg_stat_archiver view will always have a single row, containing data about the archiver process of the cluster. Such a system would show similar times while new WAL is being generated, but would differ when the sender becomes idle. The pg_statio_all_sequences view will contain one row for each sequence in the current database, showing statistics about I/O on that specific sequence. Table28.17.pg_statio_all_sequences View. This and other streaming counters for this slot can be used to tune logical_decoding_work_mem. 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 backends currently connected to this database. Waiting to allocate a new transaction ID. Waiting to read or update shared multixact state. sync: This standby server is synchronous. The parameter track_activities enables monitoring of the current command being executed by any server process. Number of index scans initiated on this index, Number of index entries returned by scans on this index, Number of live table rows fetched by simple index scans using this index.