pg_stat_get_snapshot_timestamp () timestamp with time zone, Returns the timestamp of the current statistics snapshot, or NULL if no statistics snapshot has been taken. Query identifiers are not computed by default so this field will be null unless compute_query_id parameter is enabled or a third-party module that computes query identifiers is configured. Waiting for I/O on a multixact member SLRU buffer. The following wait events are a subset of the list in Amazon Aurora PostgreSQL wait events. ; Ensure that filesystem journaling is turned off for data files and WAL files. Waiting in main loop of the archiver process. pg_blocking_pids function. Waiting for a write during a file copy operation. 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. Waiting to access the list of predicate locks held by the current serializable transaction during a parallel query. Write-Ahead Logging (WAL) is a standard method for ensuring data integrity. The pg_stat_wal_receiver view will contain only one row, showing statistics about the WAL receiver from that receiver's connected server. Thanks for letting us know we're doing a good job! Waiting for a read when creating a new WAL segment by copying an existing one. Waiting for a read from a replication slot control file. The server process is waiting for an I/O operation to complete. Waiting during base backup when throttling activity. Waiting to add or examine predicate lock information. Waiting to acquire a lock on page of a relation. Waiting for data to reach durable storage while assigning a new WAL sync method. IPC: The server process is waiting for some activity from another process in the server. Priority of this standby server for being chosen as the synchronous standby in a priority-based synchronous replication. Waiting for I/O on a commit timestamp SLRU buffer. Waiting for parallel workers to finish computing. Current overall state of this backend. PostgreSQL 's statistics collector is a subsystem that supports collection and reporting of information about server activity. BK_1935: "IObuffer_locks,ControlLock()"IOControlLockControlLockIOSlruSharedData. See, One row for each table in the current database, showing statistics about accesses to that specific table. The parameter track_counts controls whether cumulative statistics are collected about table and index accesses. your experience with the particular feature or requires further clarification, If the state is active and wait_event is non-null, it means that a query is being executed, but is being blocked somewhere in the system. 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). The parameter track_functions enables tracking of usage of user-defined functions. 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 read or update information about serializable transactions. Another important point is that when a server process is asked to display any of these statistics, it first fetches the most recent report emitted by the collector process and then continues to use this snapshot for all statistical views and functions until the end of its current transaction. Waiting for a write of a two phase state file. See, One row for each tracked function, showing statistics about executions of that function. Time when this process was started. Waiting in background writer process, hibernating. 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. Waiting to receive bytes from a shared message queue. If the current query is the first of its transaction, this column is equal to the query_start column. Returns the wait event name if this backend is currently waiting, otherwise NULL. Waiting in main loop of autovacuum launcher process. The parameter track_io_timing enables monitoring of block read and write times. If the state is active and wait_event is non-null, it means that a query is being executed, but is being blocked somewhere in the system. Waiting in main loop of startup process for WAL to arrive, during streaming recovery. 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. 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 data to reach durable storage while adding a line to the data directory lock file. Logical decoding plugins may optionally emit tracking messages; if they do not, the tracking mechanism will simply display NULL lag. Waiting for WAL from a stream at recovery. This view will only contain information on standby servers, since conflicts do not occur on primary servers. 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. See, One row for each table in the current database, showing statistics about I/O on that specific table. Possible values are: catchup: This WAL sender's connected standby is catching up with the primary. wait_event will contain a name identifying the purpose of the lightweight lock. Waiting for a replication slot control file to reach durable storage while restoring it to memory. See, One row for each index in the current database, showing statistics about accesses to that specific index. Waiting in WAL receiver to establish connection to remote server. IP address of the client connected to this WAL sender. active: The backend is executing a query. Waiting to read or update background worker state. fastpath function call: The backend is executing a fast-path function. Returns the OID of the database this backend is connected to. Waiting to elect a Parallel Hash participant to allocate more batches. async: This standby server is asynchronous. Waiting in main loop of logical replication apply process. Waiting for stats dynamic shared memory allocator access, Waiting for stats shared memory hash table access, Waiting for shared memory stats data access. Therefore it is not safe to assume that all files older than last_archived_wal have also been successfully archived. Waiting for an elected Parallel Hash participant to allocate more batches. BufferPin: The server process is waiting to access to a data buffer during a period when no other process can be examining that buffer. events. So the statistics will show static information as long as you continue the current transaction. BufferCacheHitRatio and LWLock:BufferIO wait As soon as the page is read inside the shared buffer pool, the LWLock:BufferIO lock is released. Waiting for a replication origin to become inactive so it can be dropped. 28.2.3. See. Text of this backend's most recent query. A database-wide ANALYZE is recommended after the statistics have been reset. 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 pg_stat_database_conflicts view will contain one row per database, showing database-wide statistics about query cancels occurring due to conflicts with recovery on standby servers. These access functions use a backend ID number, which ranges from one to the number of currently active backends. 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. Waiting to read or update transaction commit timestamps. Waiting for a read during recheck of the data directory lock file. Sometimes it may be more convenient to obtain just a subset of this information. Waiting in main loop of logical replication launcher process. Statistics Functions. 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 for a read of a timeline history file. gorthx on Twitter streaming: This WAL sender is streaming changes after its connected standby server has caught up with the primary. 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. A snapshot is taken the first time cumulative statistics are accessed in a transaction if stats_fetch_consistency is set to snapshot. BufferCacheHitRatio metric dips. Waiting for a write of a newly created timeline history file. Number of times transactions were spilled to disk while decoding changes from WAL for this slot. Waiting during recovery when WAL data is not available from any source (. The pg_stat_user_tables and pg_stat_sys_tables views contain the same information, but filtered to only show user and system tables respectively. Waiting for WAL to be flushed in WAL sender process. To use the Amazon Web Services Documentation, Javascript must be enabled. The server process is waiting for a lightweight lock. Waiting for other Parallel Hash participants to finish hashing the inner relation. Waiting in main loop of WAL sender process. Waiting to select the starting location of a synchronized table scan. Number of data page checksum failures detected in this database (or on a shared object), or NULL if data checksums are not enabled. Text of this backend's most recent query. Waiting to read or update the state of prepared transactions. Waiting for logical rewrite mappings to reach durable storage. See, One row per database, showing database-wide statistics. Process ID of the subscription worker process, OID of the relation that the worker is synchronizing; null for the main apply worker, Last write-ahead log location received, the initial value of this field being 0, Process ID of a backend or WAL sender process, Version of SSL in use, or NULL if SSL is not in use on this connection, Name of SSL cipher in use, or NULL if SSL is not in use on this connection, Number of bits in the encryption algorithm used, or NULL if SSL is not used on this connection, True if SSL compression is in use, false if not, or NULL if SSL is not in use on this connection, Distinguished Name (DN) field from the client certificate used, or NULL if no client certificate was supplied or if SSL is not in use on this connection. 106 . Time at which these statistics were last reset. NULL if this process is a parallel group leader or does not participate in parallel query. Restrict the maximum number of connections to the database as a best practice. 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. 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. Waiting for WAL buffers to be written to disk. This event type indicates a process waiting for activity in its main processing loop. Waiting for background worker to start up. Timeout: The server process is waiting for a timeout to expire. 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. The pg_stat_all_tables view will contain one row for each table in the current database (including TOAST tables), showing statistics about accesses to that specific table. Then identify which query 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. Possible values are: Wait event name if backend is currently waiting, otherwise NULL. This standby's xmin horizon reported by hot_standby_feedback. Waiting for I/O on a multixact_member buffer. Resets statistics for a single table or index in the current database or shared across all databases in the cluster to zero. Waiting to add a message to the shared catalog invalidation queue. 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 read or update multixact offset mappings. Its 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. See Table28.4. Waiting for a relation data file to be truncated. If state is active this field shows the currently executing query. 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 sub-transaction SLRU cache. This block has to be read from outside the shared buffer pool, defined by the This counter is incremented each time a transaction is streamed, and the same transaction may be streamed multiple times. Waiting to replace a page in WAL buffers. Process ID of the parallel group leader, if this process is a parallel query worker. Avoid PostgreSQL LWLock:buffer_content locks in Amazon Aurora: Tips and best practices. The pg_stat_ssl view will contain one row per backend or WAL sender process, showing statistics about SSL usage on this connection. Top-level transaction identifier of this backend, if any. However, they are also used to ensure mutual exclusion for certain internal operations such as relation extension. 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. Waiting for I/O on a transaction status SLRU buffer. Such a system would show similar times while new WAL is being generated, but would differ when the sender becomes idle. The fields returned are a subset of those in the pg_stat_activity view. You Total number of WAL full page images generated, Number of times WAL data was written to disk because WAL buffers became full. Waiting for I/O on a multixact offset buffer. The next use of statistical information will (when in snapshot mode) cause a new snapshot to be built or (when in cache mode) accessed statistics to be cached. 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. The pg_stat_all_tables view will contain one row for each table in the current database (including TOAST tables), showing statistics about accesses to that specific table. Additional functions related to the cumulative statistics system are listed in Table28.34. 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). A process acquires an LWLock in a shared mode to read from the buffer and an exclusive mode to write to the buffer. The LWLock:BufferIO wait event precedes the IO:DataFileRead wait event. Number of times WAL buffers were written out to disk via XLogWrite request. The last article introduced SpinLock in PostgreSQL. The functions for per-function statistics take a function OID. Waiting for the page number needed to continue a parallel B-tree scan to become available. 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. Returns the process ID of the server process attached to the current session. Waiting for data to reach durable storage while creating the data directory lock file. Waiting for background worker to shut down. Waiting for I/O on a clog (transaction status) buffer. See, One row per database, showing database-wide statistics about query cancels due to conflict with recovery on standby servers. Waiting for the group leader to update transaction status at end of a parallel operation. pg_stat_get_activity ( integer ) setof record. The per-index statistics are particularly useful to determine which indexes are being used and how effective they are. Waiting to acquire a speculative insertion lock. The pg_stat_bgwriter view will always have a single row, containing global data for the cluster. Indexes can be used by simple index scans, bitmap index scans, and the optimizer. Waiting for a replication slot to become inactive so it can be dropped. The parameter track_wal_io_timing enables monitoring of WAL write times. Waiting for WAL buffers to be written to disk. Number of disk blocks read from this table, Number of disk blocks read from all indexes on this table, Number of buffer hits in all indexes on this table, Number of disk blocks read from this table's TOAST table (if any), Number of buffer hits in this table's TOAST table (if any), Number of disk blocks read from this table's TOAST table indexes (if any), Number of buffer hits in this table's TOAST table indexes (if any). Waiting to update limits on transaction id and multixact consumption. For details such as the functions' names, consult the definitions of the standard views. 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. Waiting for SLRU data to reach durable storage following a page write. Use partitioned tables (which also have partitioned indexes). This is controlled by configuration parameters that are normally set in postgresql.conf. 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. Waiting to access the list of finished serializable transactions. Waiting to add a message in shared invalidation queue. 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. (See Chapter20 for details about setting configuration parameters.). This counts top-level transactions only, and is not incremented for subtransactions. IO: The server process is waiting for a IO to complete. Resets some cluster-wide statistics counters to zero, depending on the argument. Serial number of the client certificate, or NULL if no client certificate was supplied or if SSL is not in use on this connection. This function is restricted to superusers by default, but other users can be granted EXECUTE to run the function. block. The pg_stat_activity view will have one row per server process, showing information related to the current activity of that process. Presently, the collector can count accesses to tables and indexes in both disk-block and individual-row terms. Waiting for a write to a replication slot control file. The server process is waiting for some interaction with another server process. Cumulative statistics are collected in shared memory. The LWLock:BufferIO event occurs when Aurora PostgreSQL or RDS for PostgreSQL is waiting for other processes to finish their input/output (I/O) operations when concurrently trying to access a page. Possible values are: Top-level transaction identifier of this backend, if any. Waiting for startup process to send initial data for streaming replication. ru> Date: 2015-11-19 14:04:28 Message-ID: 20151119170428.490de41d lp [Download RAW message or body] Thank you for the review. This field is truncated if the principal is longer than NAMEDATALEN (64 characters in a standard build).