Waiting for parallel bitmap scan to become initialized. Waiting in main loop of logical replication apply process. These numbers do not act as stated above; instead they update continuously throughout the transaction. (Conflicts occur only on standby servers; see, Number of temporary files created by queries in this database. Waiting for WAL buffers to be written to disk. The parameter track_functions enables tracking of usage of user-defined functions. Resets statistics of the replication slot defined by the argument. backup: This WAL sender is sending a backup. (To prevent ordinary users from hiding their activity from the administrator, only superusers are allowed to change these parameters with SET.). The pg_stat_archiver view will always have a single row, containing data about the archiver process of the cluster. Waiting for a write while creating the data directory lock file. See, One row for each index in the current database, showing statistics about I/O on that specific index. pg_stat_get_backend_pid ( integer ) integer, pg_stat_get_backend_start ( integer ) timestamp with time zone. After v9.5, the buffer cache is protected by 128 hash tables each protected by a LWLock. Connection string used by this WAL receiver, with security-sensitive fields obfuscated. operations, Large or bloated indexes that require the engine to read more pages than necessary into the shared buffer pool, Lack of indexes that forces the DB engine to read more pages from the tables than necessary, Checkpoints occurring too frequently or needing to flush too many modified pages, Sudden spikes for database connections trying to perform operations on the same page. Waiting to read or update vacuum-related information for a B-tree index. wait_event will identify the specific wait point. Port number of the PostgreSQL instance this WAL receiver is connected to. your workload peak time if you see LWLock:BufferIO coinciding with Waiting to read or truncate multixact information. Waiting for I/O on a multixact member SLRU buffer. The server process is waiting for a timeout to expire. Conversely, if it's known that statistics are only accessed once, caching accessed statistics is unnecessary and can be avoided by setting stats_fetch_consistency to none. 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. potential: This standby server is now asynchronous, but can potentially become synchronous if one of current synchronous ones fails. Table28.6. 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 and flushed it (but not yet applied it). Waiting for the page number needed to continue a parallel B-tree scan to become available. Waiting for a logical replication remote server to send data for initial table synchronization. From the Actions drop-down menu, choose Create Read Replica. Number of deadlocks detected in this database. All temporary files are counted, regardless of why the temporary file was created, and regardless of the log_temp_files setting. This function is restricted to superusers by default, but other users can be granted EXECUTE to run the function. The pg_stat_bgwriter view will always have a single row, containing global data for the cluster. This should not be used for data integrity checks. Waiting to access the serializable transaction conflict SLRU cache. The functions for per-function statistics take a function OID. 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. For client backends, this is the time the client connected to the server. Waiting for a write when creating a new WAL segment by copying an existing one. Waiting for a write to the relation map file. The new locking scheme avoids grabbing system-wide exclusive locks in common code paths. > However, someone with deeper knowledge of page pinning and buffer manager > internals could certainly devise a better solution. Waiting to synchronize workers during Parallel Hash Join plan execution. See, One row for each sequence in the current database, showing statistics about I/O on that specific sequence. Waiting to read or write relation cache initialization file. 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. 105 #define BUFFER_MAPPING_LWLOCK_OFFSET NUM_INDIVIDUAL_LWLOCKS. If you see anything in the documentation that is not correct, does not match idle in transaction (aborted): This state is similar to idle in transaction, except one of the statements in the transaction caused an error. If a backend is in the active state, it may or may not be waiting on some event. Waiting to elect a Parallel Hash participant to allocate a hash table. 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. See, One row for each tracked function, showing statistics about executions of that function. Principal used to authenticate this connection, or NULL if GSSAPI was not used to authenticate this connection. Waiting for any activity when processing replies from WAL receiver in WAL sender process. Simple test for lock_waits log messages. Listen The most possible reason for why you see LWLockTranche/buffer_mapping wait event in PostgreSQL Well, if you are here you probably came across an issue where your database had CPU spikes. Wait Events of Type BufferPin, Table28.8. Waiting to allocate or free a replication slot. This can be used to gauge the delay that synchronous_commit level remote_apply incurred while committing if this server was configured as a synchronous standby. Waiting to manage an extension's space allocation in shared memory. idle: The backend is waiting for a new client command. Waiting for a write to update the control file. Waiting to read or update replication slot state. 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. Per-Backend Statistics Functions, pg_stat_get_backend_idset () setof integer. Extension: The server process is waiting for activity in an extension module. Also, the collector itself emits a new report at most once per PGSTAT_STAT_INTERVAL milliseconds (500 ms unless altered while building the server). pg_stat_reset_single_function_counters ( oid ) void. The total number of rows in each table, and information about vacuum and analyze actions for each table are also counted. Waiting in WAL receiver to receive data from remote server. Heavyweight locks, also known as lock manager locks or simply locks, primarily protect SQL-visible objects such as tables. Host name of the connected client, as reported by a reverse DNS lookup of, TCP port number that the client is using for communication with this backend, or. Table28.19. Waiting for a read from a timeline history file during a walsender timeline command. Number of data page checksum failures detected in this database (or on a shared object), or NULL if data checksums are not enabled. Waiting for a replication slot control file to reach durable storage. The type of event for which the backend is waiting, if any; otherwise NULL. Waiting while sending synchronization requests to the checkpointer, because the request queue is full. TCP port number that the client is using for communication with this backend, or -1 if a Unix socket is used. Its purpose is for the same page to be read into the shared buffer. Waiting to acquire a lock on a page of a relation. Waiting to read or update the fast-path lock information. IP address of the client connected to this backend. Re: Improve WALRead() to suck data directly from WAL buffers when possible True if GSSAPI encryption is in use on this connection. There are also several other views, listed in Table28.2, available to show the accumulated statistics. The pg_stat_user_indexes and pg_stat_sys_indexes views contain the same information, but filtered to only show user and system indexes respectively. Waiting to access the shared per-process data structures (typically, to get a snapshot or report a session's transaction ID). quorum: This standby server is considered as a candidate for quorum standbys. Waiting for SSL while attempting connection. NULL if this process is a parallel group leader or does not participate in parallel query. Waiting in main loop of startup process for WAL to arrive, during streaming recovery. Number of times WAL files were synced to disk via issue_xlog_fsync request (if fsync is on and wal_sync_method is either fdatasync, fsync or fsync_writethrough, otherwise zero). See, One row for each sequence in the current database, showing statistics about I/O on that specific sequence. Waiting for the relation map file to reach durable storage. When using the statistics to monitor collected data, it is important to realize that the information does not update instantaneously. Provide feedback Waiting during base backup when throttling activity. LWLock:BufferIO - Amazon Relational Database Service AWSDocumentationAmazon RDS and Aurora DocumentationUser Guide Relevant engine versionsContextCausesActions LWLock:BufferIO We recommend different actions depending on the causes of your wait event: Observe Amazon CloudWatch metrics for correlation between sharp decreases in the Waiting for activity from child process when executing. Waiting to read or update the last value set for the transaction timestamp. See, One row per SLRU, showing statistics of operations. 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. This event type indicates a process waiting for activity in its main processing loop. pg_stat_get_backend_client_port ( integer ) integer. Thanks for letting us know we're doing a good job! Lag times work automatically for physical replication. Identifier of this backend's most recent query. Synchronous state of this standby server. The parameter track_functions enables tracking of usage of user-defined functions. Amount of decoded transaction data spilled to disk while performing decoding of changes from WAL for this slot. Alternatively, one can build custom views using the underlying cumulative statistics functions, as discussed in Section28.2.24. Waiting for a write during a file copy operation. Waiting for logical rewrite mappings to reach durable storage during a checkpoint. The pg_stat_subscription_stats view will contain one row per subscription. Waiting to read or update information about. The functions for per-function statistics take a function OID. Waiting for the group leader to clear the transaction ID at end of a parallel operation. Waiting for truncate of mapping data during a logical rewrite. * The BM_IO_IN_PROGRESS flag acts as a kind of lock, used to wait for I/O on a: buffer to complete (and in releases before 14, it was accompanied by a: per-buffer LWLock). So the displayed information lags behind actual activity. Waiting for group leader to clear transaction id at transaction end. Waiting for a read from a relation data file. idle in transaction (aborted): This state is similar to idle in transaction, except one of the statements in the transaction caused an error. 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. Waiting for a write while initializing a new WAL file. Waiting for other Parallel Hash participants to finish hashing the inner relation. See, One row per WAL sender process, showing statistics about replication to that sender's connected standby server. Waiting for I/O on a transaction status SLRU buffer. The server process is waiting for activity on a socket connected to a user application. your experience with the particular feature or requires further clarification, You The parameter track_wal_io_timing enables monitoring of WAL write times. The parameter track_activities enables monitoring of the current command being executed by any server process. However, current-query information collected by track_activities is always up-to-date. See. Waiting to acquire an exclusive pin on a buffer. Waiting for a write while adding a line to the data directory lock file. Waiting in WAL receiver to receive data from remote server. 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. This field is truncated like client_dn. Waiting for a write to a relation data file. PostgreSQL's statistics collector is a subsystem that supports collection and reporting of information about server activity. Waiting for a write of a WAL page during bootstrapping. Choose the appropriate target Region. Waiting to read or update the progress of one replication origin. See, One row for each backend (including autovacuum worker processes) running, One row for each WAL sender process streaming a base backup, showing current progress. async: This standby server is asynchronous. Waiting to retrieve or remove messages from shared invalidation queue. 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. Returns the wait event type name if this backend is currently waiting, otherwise NULL. Waiting to read or update old snapshot control information. Waiting for the termination of another backend. Waiting for a replication origin to become inactive so it can be dropped. Copyright 1996-2023 The PostgreSQL Global Development Group, PostgreSQL 15.2, 14.7, 13.10, 12.14, and 11.19 Released, 28.2.1. BufferCacheHitRatio metric dips. The optimizer also accesses indexes to check for supplied constants whose values are outside the recorded range of the optimizer statistics because the optimizer statistics might be stale. Waiting to associate a data block with a buffer in the buffer pool. If you've got a moment, please tell us how we can make the documentation better. (Conflicts occur only on standby servers; see pg_stat_database_conflicts for details.). For more information on lightweight locks, see Locking Overview. Waiting for a relation data file to be extended. Waiting to add or examine predicate lock information. Waiting for a replication origin to become inactive to be dropped. Alone the requirement of separate fsyncs and everything is pretty bothersome. Waiting to acquire a lock on a non-relation database object. When a server, including a physical replica, shuts down cleanly, a permanent copy of the statistics data is stored in the pg_stat subdirectory, so that statistics can be retained across server restarts. wait_event will identify the specific wait point. Waiting for a barrier event to be processed by all backends. Waiting to insert WAL data into a memory buffer. wait_event will identify the type of lock awaited. Waiting to access the list of predicate locks held by serializable transactions. The function pg_stat_get_backend_idset provides a convenient way to generate one row for each active backend for invoking these functions. OID of this database, or 0 for objects belonging to a shared relation. Waits for lightweight locks ( LWLock ). Waiting for a two phase state file to reach durable storage. True if GSSAPI authentication was used for this connection. LWLock- buffer_mapping. Waiting to add a message to the shared catalog invalidation queue. Most such locks protect a particular data structure in shared memory. PostgreSQL 15.2, 14.7, 13.10, 12.14, and 11.19 Released, 28.2.1. To minimize skew, stats_fetch_consistency can be set to snapshot, at the price of increased memory usage for caching not-needed statistics data. The pg_stat_user_functions view will contain one row for each tracked function, showing statistics about executions of that function. Since collection of statistics adds some overhead to query execution, the system can be configured to collect or not collect information. Possible values are: Wait event name if backend is currently waiting, otherwise NULL. 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. , LWTRANCHE_MXACTMEMBER_BUFFERS, LWTRANCHE_ASYNC_BUFFERS, LWTRANCHE_OLDSERXID_BUFFERS, LWTRANCHE_WAL_INSERT, LWTRANCHE_BUFFER_CONTENT, LWTRANCHE_BUFFER_IO_IN_PROGRESS, LWTRANCHE . 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. Waiting for the relation map file to reach durable storage. Waiting to read or update the current state of autovacuum workers. The type of event for which the backend is waiting, if any; otherwise NULL. 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. Waiting for a write of mapping data during a logical rewrite. Waiting for a two phase state file to reach durable storage. Waiting to read or update the last value set for a transaction commit timestamp. Waiting for a read of a serialized historical catalog snapshot. Waiting to send bytes to a shared message queue. Waiting to read or update multixact offset mappings. Wait Events of Type Extension. Waiting to create, drop or use a replication origin. Waiting for confirmation from a remote server during synchronous replication. 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. Ordinary users can only see all the information about their own sessions (sessions belonging to a role that they are a member of). Waiting for a replication slot control file to reach durable storage while restoring it to memory. See. Waiting for a newly created timeline history file to reach durable storage. The argument can be one of CommitTs, MultiXactMember, MultiXactOffset, Notify, Serial, Subtrans, or Xact to reset the counters for only that entry. 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. Possible values are: async: This standby server is asynchronous. If the argument is NULL, reset statistics for all subscriptions. Waiting for a read from a replication slot control file. Resets some cluster-wide statistics counters to zero, depending on the argument. LWTRANCHE_BUFFER_CONTENT @ LWTRANCHE_BUFFER_CONTENT. All temporary files are counted, regardless of why the temporary file was created, and regardless of the, Number of deadlocks detected in this database, Time spent reading data file blocks by backends in this database, in milliseconds, Time spent writing data file blocks by backends in this database, in milliseconds, 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, 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, Last time at which this table was manually vacuumed (not counting, Last time at which this table was vacuumed by the autovacuum daemon, Last time at which this table was manually analyzed, Last time at which this table was analyzed by the autovacuum daemon, Number of times this table has been manually vacuumed (not counting, 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, 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, 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), Number of disk blocks read from this index, Number of disk blocks read from this sequence, 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, Process ID of the server process handling the current session, Returns a record of information about the backend with the specified PID, or one record for each active backend in the system if, Returns the timestamp of the current statistics snapshot, Reset all statistics counters for the current database to zero (requires superuser privileges by default, but EXECUTE for this function can be granted to others. Current WAL sender state. Waiting for action on logical replication worker to finish. 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). Total number of WAL full page images generated, Number of times WAL data was written to disk because WAL buffers became full. 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. Number of WAL files that have been successfully archived, Name of the WAL file most recently successfully archived, last_archived_time timestamp with time zone, Time of the most recent successful archive operation, Number of failed attempts for archiving WAL files, Name of the WAL file of the most recent failed archival operation, last_failed_time timestamp with time zone, Time of the most recent failed archival operation. replication_slot_io: Waiting for I/O on a replication slot. A snapshot is taken the first time cumulative statistics are accessed in a transaction if stats_fetch_consistency is set to snapshot. This view will only contain information on standby servers, since conflicts do not occur on master servers. Indexes can be used by simple index scans, bitmap index scans, and the optimizer. However, current-query information collected by track_activities is always up-to-date. Waiting for startup process to send initial data for streaming replication. LWLock:buffer_mapping. finish their input/output (I/O) operations when concurrently trying to access a page. Waiting for WAL buffers to be written to disk. You can invoke pg_stat_clear_snapshot() to discard the current transaction's statistics snapshot or cached values (if any). In all other states, it shows the last query that was executed. Possible values are: Last write-ahead log location sent on this connection, Last write-ahead log location written to disk by this standby server, Last write-ahead log location flushed to disk by this standby server, Last write-ahead log location replayed into the database on this standby server, 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). Additional functions related to the cumulative statistics system are listed in Table28.34. @ LWTRANCHE_REPLICATION_SLOT_IO. Waiting for a logical replication remote server to change state. It also tracks the total number of rows in each table, and information about . 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. Waiting to find or allocate space in shared memory. Therefore, while holding an exclusive lock, a process prevents other processes from acquiring a shared or exclusive lock.