Waiting for the page number needed to continue a parallel B-tree scan to become available. Waiting for a write of a serialized historical catalog snapshot. See, At least one row per subscription, showing information about the subscription workers. idle in transaction: The backend is in a transaction, but is not currently executing a query. The server process is waiting for exclusive access to a data buffer. For details such as the functions' names, consult the definitions of the standard views. By default the query text is truncated at 1024 bytes; this value can be changed via the parameter track_activity_query_size. Waiting for SLRU data to reach durable storage following a page write. The pg_stat_bgwriter view will always have a single row, containing global data for the cluster. Waiting in WAL receiver to receive data from remote server. 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. Each individual server process transmits new statistical counts to the collector just before going idle; so a query or transaction still in progress does not affect the displayed totals. your experience with the particular feature or requires further clarification, Table28.17.pg_stat_recovery_prefetch View, Number of blocks prefetched because they were not in the buffer pool, Number of blocks not prefetched because they were already in the buffer pool, Number of blocks not prefetched because they would be zero-initialized, Number of blocks not prefetched because they didn't exist yet, Number of blocks not prefetched because a full page image was included in the WAL, Number of blocks not prefetched because they were already recently prefetched, How many bytes ahead the prefetcher is looking, How many blocks ahead the prefetcher is looking, How many prefetches have been initiated but are not yet known to have completed, 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. So the statistics will show static information as long as you continue the current transaction. Waiting to read or update sub-transaction information. The server process is waiting for a timeout to expire. please use In all other states, it shows the identifier of last query that was executed. See, One row for each table in the current database, showing statistics about accesses to that specific table. - a BufFreeList LWLock was getting acquired to find a free buffer for a page - to change the association of buffer in buffer mapping hash table a LWLock is acquired on a hash partition to which the buffer to be associated belongs and as there were just 16 such partitions, there was huge contention when multiple clients See, One row only, showing statistics about the background writer process's activity. Waiting for an elected Parallel Hash participant to allocate the initial hash table. However, these statistics do not give the entire story: due to the way in which PostgreSQL handles disk I/O, data that is not in the PostgreSQL buffer cache might still reside in the kernel's I/O cache, and might therefore still be fetched without requiring a physical read. Host name of the connected client, as reported by a reverse DNS lookup of client_addr. See, OID of the database this backend is connected to, Name of the database this backend is connected to, Name of the user logged into this backend, Name of the application that is connected to this backend. Waiting to apply WAL at recovery because it is delayed. So the displayed information lags behind actual activity. 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. See. If this field is null, it indicates that this is an internal server process. This effect can mean that you have a small shared buffers setting. Waiting to read or update shared multixact state. 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. Such a system would show similar times while new WAL is being generated, but would differ when the sender becomes idle. Returns the wait event name if this backend is currently waiting, otherwise NULL. IP address of the client connected to this WAL sender. Time when the currently active query was started, or if state is not active, when the last query was started. See, One row for each table in the current database, showing statistics about I/O on that specific table. Waiting for changes to a relation data file to reach durable storage. Waiting to receive bytes from a shared message queue. 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. 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. Number of temporary files created by queries in this database. Alternatively, you can invoke pg_stat_clear_snapshot(), which will discard the current transaction's statistics snapshot (if any). This field is truncated if the principal is longer than NAMEDATALEN (64 characters in a standard build). The pg_stat_recovery_prefetch view will contain only one row. Returns a record of information about the backend with the specified process ID, or one record for each active backend in the system if NULL is specified. PostgreSQL's statistics collector is a subsystem that supports collection and reporting of information about server activity. 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. Wait event name if backend is currently waiting, otherwise NULL. If the current query is the first of its transaction, this column is equal to the query_start column. Autovacuum worker or launcher waiting to update or read the current state of autovacuum workers. Waiting in main loop of checkpointer process. Write-Ahead Logging (WAL) is a standard method for ensuring data integrity. BK_1935: "IObuffer_locks,ControlLock()"IOControlLockControlLockIOSlruSharedData. LWLock: The backend is waiting for a lightweight lock. The pg_stat_replication_slots view will contain one row per logical replication slot, showing statistics about its usage. Table28.12.pg_stat_database_conflicts View. From the Actions drop-down menu, choose Create Read Replica. Waiting for startup process to send initial data for streaming replication. Waiting for a write during reorder buffer management. 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. See Table28.4. The pg_stat_wal_receiver view will contain only one row, showing statistics about the WAL receiver from that receiver's connected server. workload into more reader nodes. Increase the number of wal_buffers available to the database. In such cases, an older set of per-backend statistics access functions can be used; these are shown in Table28.35. Possible values are: 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, Last write-ahead log location already received and flushed to disk, the initial value of this field being the first log location used when WAL receiver is started, Timeline number of last write-ahead log location received and flushed to disk, the initial value of this field being the timeline number of the first log location used when WAL receiver is started, Send time of last message received from origin WAL sender, Receipt time of last message received from origin WAL sender, Last write-ahead log location reported to origin WAL sender, Time of last write-ahead log location reported to origin WAL sender, Replication slot name used by this WAL receiver. The parameter track_counts controls whether statistics are collected about table and index accesses. Waiting to elect a Parallel Hash participant to allocate more buckets. Waiting for a write while adding a line to the data directory lock file. In all other states, it shows the last query that was executed. 214 . Here is an example of how wait events can be viewed: The pg_stat_replication view will contain one row per WAL sender process, showing statistics about replication to that sender's connected standby server. For client backends, this is the time the client connected to the server. pg_stat_get_activity ( integer ) setof record. This has no effect in a quorum-based synchronous replication. 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. replication_origin: Waiting to read or update the replication progress. Note, however, that the existence of a session and its general properties such as its sessions user and database are visible to all users. Then identify which query See, One row per database, showing database-wide statistics. 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. TCP port number that the client is using for communication with this backend, or -1 if a Unix socket is used. 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 for a two phase state file to reach durable storage. Waiting for a write to update the control file. 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. Waiting to update limits on transaction id and multixact consumption. Ordinary users can only see all the information about their own sessions (sessions belonging to a role that they are a member of). Number of data page checksum failures detected in this database (or on a shared object), or NULL if data checksums are not enabled. (To prevent ordinary users from hiding their activity from the administrator, only superusers are allowed to change these parameters with SET.). Waiting for parallel workers to finish computing. A backend process wants to read a page into shared memory. Current WAL sender state. Waiting to manage space allocation in shared memory. Waiting for activity from child process when executing. See, One row for each tracked function, showing statistics about executions of that function. Waiting for I/O on a commit timestamp SLRU buffer. Waiting for WAL to be flushed in WAL sender process. Waiting during recovery when WAL data is not available from any source (. Waiting to read or update replication slot state. It can be joined to pg_stat_activity or pg_stat_replication on the pid column to get more details about the connection. LWTRANCHE_BUFFER_CONTENT @ LWTRANCHE_BUFFER_CONTENT. See, Time when the current transaction was started. Doing this helps Waiting to add a message in shared invalidation queue. LWLock:buffer_mapping. 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. Presently, the collector can count accesses to tables and indexes in both disk-block and individual-row terms. Presently, accesses to tables and indexes in both disk-block and individual-row terms are counted. Waiting in main loop of WAL receiver process. pg_stat_get_backend_activity ( integer ) text. Waiting to perform an operation on a list of locks held by serializable transactions. Waiting for a barrier event to be processed by all backends. Waiting for a read of a serialized historical catalog snapshot. Returns the IP address of the client connected to this backend. The combination of certificate serial number and certificate issuer uniquely identifies a certificate (unless the issuer erroneously reuses serial numbers).