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(See Chapter20 for details about setting configuration parameters.). See, Only one row, showing statistics about blocks prefetched during recovery. Waiting for other Parallel Hash participants to finish hashing the inner relation. (Some locks have specific names; others are part of a group of locks each with a similar purpose.). This can be used to gauge the delay that, Time elapsed between flushing recent WAL locally and receiving notification that this standby server has written, flushed and applied it. All temporary files are counted, regardless of why the temporary file was created (e.g., sorting or hashing), and regardless of the, Total amount of data written to temporary files by queries in this database. OID of this database, or 0 for objects belonging to a shared relation. To minimize skew, stats_fetch_consistency can be set to snapshot, at the price of increased memory usage for caching not-needed statistics data. IO: The server process is waiting for a IO to complete. This is used by system processes waiting for activity in their main processing loop. Principal used to authenticate this connection, or NULL if GSSAPI was not used to authenticate this connection. Waiting for I/O on a multixact offset SLRU buffer. Waiting in background writer process, hibernating. Logical decoding plugins may optionally emit tracking messages; if they do not, the tracking mechanism will simply display NULL lag. This counter is incremented each time a transaction is streamed, and the same transaction may be streamed multiple times. The parameter track_functions enables tracking of usage of user-defined functions. Attempts to free it PostgreSQL Entangled in Locks - PGCon See, One row for each tracked function, showing statistics about executions of that function. Extension: The server process is waiting for activity in an extension module. 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. 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. Waiting for group leader to clear transaction id at transaction end. Several predefined views, listed in Table28.1, are available to show the current state of the system. The LWLock that this article will introduce is a lightweight lock (Lightweight Lock) based on SpinLock. The parameter track_wal_io_timing enables monitoring of WAL write times. Total amount of time spent writing WAL buffers to disk via XLogWrite request, in milliseconds (if track_wal_io_timing is enabled, otherwise zero). 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. 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. 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. Table28.19.pg_stat_subscription_stats View, Number of times an error occurred while applying changes, Number of times an error occurred during the initial table synchronization. The new locking scheme avoids grabbing system-wide exclusive locks in common code paths. 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 rows returned by queries in this database, Number of rows fetched by queries 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. Waiting in background writer process, hibernating. Waiting for a write of a newly created timeline history file. Waiting for a buffered file to be truncated. Waiting to access the transaction status SLRU cache. quorum: This standby server is considered as a candidate for quorum standbys. The next use of statistical information will cause a new snapshot to be fetched. Waiting for a write of logical rewrite mappings. Waiting to read or update notification messages. 214 . Waiting for confirmation from remote server during synchronous replication. active: The backend is executing a query. Monitoring systems should choose whether to represent this as missing data, zero or continue to display the last known value. Thus, the server expects something to happen that is independent of its internal processes. buffer_io: Waiting for I/O on a data page. 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. Waiting during recovery when WAL data is not available from any source (. Extensions can add LWLock types to the list shown in Table28.12. Waiting for another process to be attached to a shared message queue. Waiting to allocate or free a replication slot. Time spent reading data file blocks by backends in this database, in milliseconds (if track_io_timing is enabled, otherwise zero), Time spent writing data file blocks by backends in this database, in milliseconds (if track_io_timing is enabled, otherwise zero), Time spent by database sessions in this database, in milliseconds (note that statistics are only updated when the state of a session changes, so if sessions have been idle for a long time, this idle time won't be included), Time spent executing SQL statements in this database, in milliseconds (this corresponds to the states active and fastpath function call in pg_stat_activity), idle_in_transaction_time double precision, Time spent idling while in a transaction in this database, in milliseconds (this corresponds to the states idle in transaction and idle in transaction (aborted) in pg_stat_activity), Total number of sessions established to this database, Number of database sessions to this database that were terminated because connection to the client was lost, Number of database sessions to this database that were terminated by fatal errors, Number of database sessions to this database that were terminated by operator intervention. This is controlled by configuration parameters that are normally set in postgresql.conf. The fields returned are a subset of those in the pg_stat_activity view. Did this page help you? In some cases, the name assigned by an extension will not be available in all server processes; so an LWLock wait event might be reported as just extension rather than the extension-assigned name. sync: This standby server is synchronous. Waiting for a replication slot control file to reach durable storage while restoring it to memory. Waiting to manage an extension's space allocation in shared memory. Connection string used by this WAL receiver, with security-sensitive fields obfuscated. 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 to the relation map file. 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. pg_stat_reset_single_function_counters ( oid ) void. Sometimes it may be more convenient to obtain just a subset of this information. Waiting for a write of a WAL page during bootstrapping. This should not be used for data integrity checks. 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. For an asynchronous standby, the replay_lag column approximates the delay before recent transactions became visible to queries. Waits for lightweight locks ( LWLock ). 39919 LWLock buffer_mapping 5119 Client ClientRead 3116 IO DataFileRead With C-Hash Event Count Event Type Event Name Waiting for a write of logical rewrite mappings. Waiting to read or update the control file or creation of a new WAL file. For more information, see LWLock:buffer_mapping. Detailed Description . pg_stat_reset_single_table_counters ( oid ) void. Alternatively, one can build custom views using the underlying cumulative statistics functions, as discussed in Section28.2.24. Waiting for a relation data file to be extended. (To prevent ordinary users from hiding their activity from the administrator, only superusers are allowed to change these parameters with SET.). Waiting to read or update dynamic shared memory state. wait_event will identify the specific wait point. Waiting to access the list of predicate locks held by the current serializable transaction during a parallel query. For client backends, this is the time the client connected to the server. This facility is independent of the collector process. PostgreSQL: Documentation: 11: 28.2. The Statistics Collector Waiting to access the shared per-process data structures (typically, to get a snapshot or report a session's transaction ID). If the argument is NULL, resets statistics for all the replication slots. The pg_stat_recovery_prefetch view will contain only one row. This is consistent with the goal of measuring synchronous commit and transaction visibility delays for recent write transactions. Waiting for logical rewrite mappings to reach durable storage. If you've got a moment, please tell us how we can make the documentation better. Waiting for the page number needed to continue a parallel B-tree scan to become available. In such cases, an older set of per-backend statistics access functions can be used; these are shown in Table28.20. Waiting to read or update dynamic shared memory allocation information. Wait Events of Type Extension. Waiting to retrieve messages from the shared catalog invalidation queue. 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 an update to the control file to reach durable storage. Waiting for a newly initialized WAL file to reach durable storage. The per-table and per-index functions take a table or index OID. These numbers do not act as stated above; instead they update continuously throughout the transaction. Waiting for a write to update the control file. The generated IO patterns are also much worse. See, One row per WAL sender process, showing statistics about replication to that sender's connected standby server. This counter is incremented each time a transaction is spilled, and the same transaction may be spilled multiple times. Waiting to acquire an exclusive pin on a buffer. Waiting to access a parallel query's information about type modifiers that identify anonymous record types. 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. Waiting in main loop of autovacuum launcher process. Waiting for a read when creating a new WAL segment by copying an existing one. If the argument is NULL, all counters shown in the pg_stat_slru view for all SLRU caches are reset. replication_origin: Waiting to read or update the replication progress. This field is truncated if the DN field is longer than NAMEDATALEN (64 characters in a standard build). Please refer to your browser's Help pages for instructions. 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. Amazon Aurora PostgreSQL wait events - Amazon Aurora ), 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 an elected Parallel Hash participant to allocate the initial hash table. A transaction can also see its own statistics (as yet untransmitted to the collector) in the views pg_stat_xact_all_tables, pg_stat_xact_sys_tables, pg_stat_xact_user_tables, and pg_stat_xact_user_functions. Per-Backend Statistics Functions, pg_stat_get_backend_idset () setof integer. Pointers to free buffers and to the next victim are protected by one buffer strategy lock spinlock. 28.2.3. Waiting to find or allocate space in shared memory. Waiting in main loop of checkpointer process. 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. Waiting in WAL receiver to establish connection to remote server. This effect can mean that you have a small shared buffers setting. . Waiting in WAL receiver to establish connection to remote server. Waiting for a write of a WAL page during bootstrapping. Number of sequential scans initiated on this table, Number of live rows fetched by sequential scans, Number of index scans initiated on this table, Number of live rows fetched by index scans, Number of rows updated (includes HOT updated rows), Number of rows HOT updated (i.e., with no separate index update required), Estimated number of rows modified since this table was last analyzed, Estimated number of rows inserted since this table was last vacuumed, Last time at which this table was manually vacuumed (not counting VACUUM FULL), Last time at which this table was vacuumed by the autovacuum daemon, Last time at which this table was manually analyzed, last_autoanalyze timestamp with time zone, Last time at which this table was analyzed by the autovacuum daemon, Number of times this table has been manually vacuumed (not counting VACUUM FULL), Number of times this table has been vacuumed by the autovacuum daemon, Number of times this table has been manually analyzed, Number of times this table has been analyzed by the autovacuum daemon.