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. Heavyweight locks, also known as lock manager locks or simply locks, primarily protect SQL-visible objects such as tables. See, One row per database, showing database-wide statistics. However, they are also used to ensure mutual exclusion for certain internal operations such as relation extension. Waiting for a two phase state file to reach durable storage. Waiting to acquire an exclusive lock to truncate off any empty pages at the end of a table vacuumed. Waiting in main loop of logical replication launcher process. Per-Backend Statistics Functions, Copyright 1996-2023 The PostgreSQL Global Development Group. Using pg_stat_reset() also resets counters that autovacuum uses to determine when to trigger a vacuum or an analyze. Host name of the connected client, as reported by a reverse DNS lookup of client_addr. This facility is independent of the collector process. Javascript is disabled or is unavailable in your browser. Number of deadlocks detected in this database. idle: The backend is waiting for a new client command. For more information, see LWLock:buffer_content (BufferContent). In rows about other sessions, many columns will be null. Waiting for a write when creating a new WAL segment by copying an existing one. The server process is waiting for some interaction with another server process. OID of this database, or 0 for objects belonging to a shared relation. Waiting to read or update the current state of autovacuum workers. See, One row for each index in the current database, showing statistics about I/O on that specific index. Users interested in obtaining more detailed information on PostgreSQL I/O behavior are advised to use the PostgreSQL statistics views in combination with operating system utilities that allow insight into the kernel's handling of I/O. Note that this includes the transactions that are streamed and/or spilled. The generated IO patterns are also much worse. Waiting for a write of mapping data during a logical rewrite. Waiting in background writer process, hibernating. Waiting for data to reach durable storage while assigning a new WAL sync method. Waiting for a write to the relation map file. Waiting for WAL buffers to be written to disk. buffer_mapping: Waiting to associate a data block with a buffer in the buffer pool. 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. It can be joined to pg_stat_activity or pg_stat_replication on the pid column to get more details about the connection. You can split your In addition, background workers registered by extensions may have additional types. These numbers do not act as stated above; instead they update continuously throughout the transaction. Wait Events of Type BufferPin, Table28.8. Waiting in main loop of syslogger process. Waiting to retrieve or remove messages from shared invalidation queue. The functions for per-function statistics take a function OID. Presently, accesses to tables and indexes in both disk-block and individual-row terms are counted. It can be joined to pg_stat_activity or pg_stat_replication on the pid column to get more details about the connection. Waiting for another process to be attached to a shared message queue. The parameter track_counts controls whether cumulative statistics are collected about table and index accesses. Heavyweight locks, also known as lock manager locks or simply locks, primarily protect SQL-visible objects such as tables. 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 for SSL while attempting connection. Waiting to access the serializable transaction conflict SLRU cache. For example, to show the PIDs and current queries of all backends: Table28.20. BK_1935: "IObuffer_locks,ControlLock()"IOControlLockControlLockIOSlruSharedData. See, Only one row, showing statistics about blocks prefetched during recovery. The parameter track_io_timing enables monitoring of block read and write times. 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 to insert WAL into a memory buffer. This documentation is for an unsupported version of PostgreSQL. Amount of transaction data decoded for sending transactions to the decoding output plugin while decoding changes from WAL for this slot. The pg_stat_wal_receiver view will contain only one row, showing statistics about the WAL receiver from that receiver's connected server. * 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). Table28.19. The new locking scheme avoids grabbing system-wide exclusive locks in common code paths. Waiting to apply WAL during recovery because of a delay setting. Waiting for data to reach durable storage while creating the data directory lock file. 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. Waiting for a write while initializing a new WAL file. Synchronous state of this standby server. 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. 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. Number of times WAL buffers were written out to disk via XLogWrite request. This and other spill counters can be used to gauge the I/O which occurred during logical decoding and allow tuning logical_decoding_work_mem. Waiting to acquire an advisory user lock. a page) has to be retrieved outside the shared buffer pool. Statistics Collection Configuration, One row per server process, showing information related to the current activity of that process, such as state and current query. Number of temporary files created by queries in this database. (For example, in psql you could issue \d+ pg_stat_activity.) See, One row for each sequence in the current database, showing statistics about I/O on that specific sequence. Using pg_stat_reset() also resets counters that autovacuum uses to determine when to trigger a vacuum or an analyze. Sometimes it may be more convenient to obtain just a subset of this information. Waiting for a timeline history file received via streaming replication to reach durable storage. The pg_stat_archiver view will always have a single row, containing data about the archiver process of the cluster. This view will only contain information on standby servers, since conflicts do not occur on master servers. (Conflicts occur only on standby servers; see pg_stat_database_conflicts for details.). The reported lag times are not predictions of how long it will take for the standby to catch up with the sending server assuming the current rate of replay. Waiting for logical replication remote server to change state. Waiting for a write of a WAL page during bootstrapping. This field is truncated if the DN field is longer than NAMEDATALEN (64 characters in a standard build). A database-wide ANALYZE is recommended after the statistics have been reset. When the number of actual disk reads is much smaller than the number of buffer hits, then the cache is satisfying most read requests without invoking a kernel call. Waiting to replace a page in WAL buffers. Table28.17.pg_statio_all_sequences View. Waiting for I/O on a multixact member SLRU buffer. It also tracks the total number of rows in each table, and information about . Waiting for parallel workers to finish computing. Priority of this standby server for being chosen as the synchronous standby in a priority-based synchronous replication. Please refer to your browser's Help pages for instructions. Presently, the collector can count accesses to tables and indexes in both disk-block and individual-row terms. wait_event will contain a name identifying the purpose of the lightweight lock. Process ID of the parallel group leader, if this process is a parallel query worker. Its Waiting to receive bytes from a shared message queue. This field is truncated if the principal is longer than NAMEDATALEN (64 characters in a standard build). The server process is waiting for an I/O operation to complete. Time when this process was started. postgres 26 Heap_Insert Waiting to read or update sub-transaction information. Resets some cluster-wide statistics counters to zero, depending on the argument. I've made . pg_stat_get_backend_wait_event ( integer ) text. Waiting to get a snapshot or clearing a transaction id at transaction end. Returns the time when the backend's current transaction was started. pg_stat_reset_replication_slot ( text ) void. The buffer_mapping LWLock wait event will be . 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. 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. Waiting for WAL files required for a backup to be successfully archived. Waiting for other Parallel Hash participants to finish loading a hash table. Waiting to access the multixact member SLRU cache. If you've got a moment, please tell us what we did right so we can do more of it. This has no effect in a quorum-based synchronous replication. Did this page help you? idle in transaction: The backend is in a transaction, but is not currently executing a query. Waiting for logical replication remote server to send data for initial table synchronization. Waiting for a read of a two phase state file. See, One row for each table in the current database, showing statistics about accesses to that specific table. For an asynchronous standby, the replay_lag column approximates the delay before recent transactions became visible to queries. See, One row per connection (regular and replication), showing information about SSL used on this connection. Waiting to send bytes to a shared message queue. Then identify which query See, One row per WAL sender process, showing statistics about replication to that sender's connected standby server. Waiting to read or update transaction commit timestamps. In a bitmap scan the output of several indexes can be combined via AND or OR rules, so it is difficult to associate individual heap row fetches with specific indexes when a bitmap scan is used. Waiting for an asynchronous prefetch from a relation data file. This is consistent with the goal of measuring synchronous commit and transaction visibility delays for recent write transactions. Waiting for startup process to send initial data for streaming replication. Waiting for a write when creating a new WAL segment by copying an existing one. 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. Number of data page checksum failures detected in this database (or on a shared object), or NULL if data checksums are not enabled. Copyright 1996-2023 The PostgreSQL Global Development Group, PostgreSQL 15.2, 14.7, 13.10, 12.14, and 11.19 Released, 28.2.1. 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. Buffer pin waits can be protracted if another process holds an open cursor that last read data from the buffer in question. [prev in list] [next in list] [prev in thread] [next in thread] List: postgresql-general Subject: Re: [HACKERS] [PATCH] Refactoring of LWLock tranches From: Ildus Kurbangaliev <i.kurbangaliev postgrespro ! Waiting in main loop of background writer process. A process can wait for the data needed from a client ( Client) or another process ( IPC ). The pg_stat_activity view will have one row per server process, showing information related to the current activity of that process. Waiting for a read from a replication slot control file. 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. Waiting in main loop of WAL writer process. Waiting for a write while creating the data directory lock file. Possible values are: Top-level transaction identifier of this backend, if any. You This category is useful for modules to track custom waiting points. For tranches registered by extensions, the name is specified by extension and this will be displayed as wait_event. Waiting for a read during a file copy operation. Additional Statistics Functions. sync: This standby server is synchronous. From the Actions drop-down menu, choose Create Read Replica. block. Waiting to update limits on transaction id and multixact consumption. Total number of WAL full page images generated, Number of times WAL data was written to disk because WAL buffers became full. Resetting these counters can cause autovacuum to not perform necessary work, which can cause problems such as table bloat or out-dated table statistics. In a bitmap scan the output of several indexes can be combined via AND or OR rules, so it is difficult to associate individual heap row fetches with specific indexes when a bitmap scan is used. (For example, in psql you could issue \d+ pg_stat_activity.) See, At least one row per subscription, showing information about the subscription workers. Number of blocks zeroed during initializations, Number of times disk blocks were found already in the SLRU, so that a read was not necessary (this only includes hits in the SLRU, not the operating system's file system cache), Number of disk blocks written for this SLRU, Number of blocks checked for existence for this SLRU, Number of flushes of dirty data for this SLRU. Waiting for parallel query dynamic shared memory allocation. Number of times transactions were spilled to disk while decoding changes from WAL for this slot. (The path case can be distinguished because it will always be an absolute path, beginning with /.). 39919 LWLock buffer_mapping 5119 Client ClientRead 3116 IO DataFileRead With C-Hash Event Count Event Type Event Name Waiting to read or write a data page in memory. Waiting for a replication slot control file to reach durable storage while restoring it to memory. 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. See, One row for each table in the current database, showing statistics about I/O on that specific table. IP address of the client connected to this backend. Waiting to read or update old snapshot control information. Waiting to acquire an advisory user lock. Time when this process' current transaction was started, or null if no transaction is active. Waiting for background worker to shut down. Waiting for background worker to start up. Restrict the maximum number of connections to the database as a best practice. PostgreSQL's cumulative statistics system supports collection and reporting of information about server activity. Waiting to get the start location of a scan on a table for synchronized scans. The parameter track_functions enables tracking of usage of user-defined functions. Waits for a buffer pin ( BufferPin ). Waiting for the relation map file to reach durable storage. Doing this helps Waiting for a read of a two phase state file. 213 * Prior to PostgreSQL 9.4, we used an enum type called LWLockId to refer. Total amount of time spent writing WAL buffers to disk via XLogWrite request, in milliseconds (if track_wal_io_timing is enabled, otherwise zero). 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. LWLock- buffer_mapping. 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. This can be used to gauge the delay that synchronous_commit level remote_write incurred while committing if this server was configured as a synchronous standby. Waiting for SLRU data to reach durable storage following a page write. 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 for a write to a replication slot control file. This counter is incremented each time a transaction is streamed, and the same transaction may be streamed multiple times. Prevent sudden database connection spikes by using a connection pool. backup: This WAL sender is sending a backup. However, current-query information collected by track_activities is always up-to-date. For more information on lightweight locks, see Locking Overview. The per-index statistics are particularly useful to determine which indexes are being used and how effective they are. 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). True if GSSAPI authentication was used for this connection. Waiting in main loop of WAL sender process. Waiting for parallel bitmap scan to become initialized. Waiting for a replication origin to become inactive to be dropped. Waiting to read or update the replication progress. The pg_stat_user_functions view will contain one row for each tracked function, showing statistics about executions of that function. Alternatively, one can build custom views using the underlying statistics functions, as discussed in Section28.2.3. Therefore it is not safe to assume that all files older than last_archived_wal have also been successfully archived. Waiting for a replication slot to become inactive to be dropped. Waiting for an elected Parallel Hash participant to allocate a hash table. wait_event will identify the specific wait point. In all other states, it shows the identifier of last query that was executed. Only directly connected standbys are listed; no information is available about downstream standby servers. True if GSSAPI encryption is in use on this connection. 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 live rows fetched by sequential scans and index entries returned by index scans in this database, Number of live rows fetched by index scans 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. See, Only one row, showing statistics about the WAL receiver from that receiver's connected server. 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 to elect a Parallel Hash participant to allocate a hash table. For details such as the functions' names, consult the definitions of the standard views. Common causes for the LWLock:BufferIO event to appear in top waits include the following: Multiple backends or connections trying to access the same page that's replication_slot_io: Waiting for I/O on a replication slot. This function is restricted to superusers by default, but other users can be granted EXECUTE to run the function. When the server 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. The fields returned are a subset of those in the pg_stat_activity view. quorum: This standby server is considered as a candidate for quorum standbys. The LWLock:BufferIO event occurs when Aurora PostgreSQL or RDS for PostgreSQL is waiting for other processes to Waiting for I/O on a commit timestamp SLRU buffer. Waiting to acquire a speculative insertion lock. Waiting to access the transaction status SLRU cache. Waiting for a read of a serialized historical catalog snapshot. Waiting to acquire a lock on a page of a relation. Waiting for a write to a relation data file. See, One row per database, showing database-wide statistics about query cancels due to conflict with recovery on standby servers. Waiting for a replication slot to become inactive so it can be dropped. @ LWTRANCHE_REPLICATION_SLOT_IO. The server process is waiting for some condition defined by an extension module. This and other streaming counters for this slot can be used to tune logical_decoding_work_mem. IP address of the client connected to this WAL sender. 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 to add a message in shared invalidation queue. 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. 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). quorum: This standby server is considered as a candidate for quorum standbys. The pg_stat_database view will contain one row for each database in the cluster, plus one for shared objects, showing database-wide statistics. The statistics collector transmits the collected information to other PostgreSQL processes through temporary files. Waiting to read or update the last value set for a transaction commit timestamp. Lag times work automatically for physical replication. The parameter track_activities enables monitoring of the current command being executed by any server process. Waiting to read or update the state of logical replication workers. Additional Statistics Functions. 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. Waiting for a read from a relation data file. Waiting to acquire an exclusive pin on a buffer. Sometimes it may be more convenient to obtain just a subset of this information. The pg_stat_user_functions view will contain one row for each tracked function, showing statistics about executions of that function. In such cases, an older set of per-backend statistics access functions can be used; these are shown in Table28.20. Waiting for changes to a relation data file to reach durable storage. Waiting for an elected Parallel Hash participant to finish allocating more buckets. sync: This standby server is synchronous. Waiting in main loop of logical launcher process. Waiting for SLRU data to reach durable storage during a checkpoint or database shutdown. Waiting for the termination of another backend. Waiting for a write while adding a line to the data directory lock file. Waiting to acquire a speculative insertion lock. Waiting in WAL receiver to establish connection to remote server. The pg_stat_archiver view will always have a single row, containing data about the archiver process of the cluster. 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. 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 to write a protocol message to a shared message queue. The LWLock:BufferIO event occurs when RDS for PostgreSQL or Aurora PostgreSQL is waiting for other processes to finish their I/O operations. There is no order to the granting of LWLocks and in a high concurrency system this can cause contention. Its purpose is for the same page to be read into the shared buffer. Note that only tables, indexes, and functions in the current database can be seen with these functions. Postgres Source Code Docs: Locking Overview. See, One row for each table in the current database, showing statistics about I/O on that specific table. Waiting in main loop of logical apply process. 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. However, current-query information collected by track_activities is always up-to-date. Possible values are: active: The backend is executing a query. Waiting for I/O on a multixact offset SLRU buffer. Current overall state of this backend. Priority of this standby server for being chosen as the synchronous standby in a priority-based synchronous replication. We recommend different actions depending on the causes of your wait event: Observe Amazon CloudWatch metrics for correlation between sharp decreases in the Waiting to read or truncate multixact information. Waiting to read or update vacuum-related information for a B-tree index. Several predefined views, listed in Table28.1, are available to show the current state of the system. The per-index statistics are particularly useful to determine which indexes are being used and how effective they are. Most such locks protect a particular data structure in shared memory. Waiting to perform an operation on a list of locks held by serializable transactions. Possible types are autovacuum launcher, autovacuum worker, logical replication launcher, logical replication worker, parallel worker, background writer, client backend, checkpointer, archiver, startup, walreceiver, walsender and walwriter.