Time when the currently active query was started, or if state is not active, when the last query was started. Waiting for an elected Parallel Hash participant to allocate a hash table. The IO:DataFileRead wait event occurs while data is 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. The pg_statio_ views are primarily useful to determine the effectiveness of the buffer cache. The pg_stat_wal_receiver view will contain only one row, showing statistics about the WAL receiver from that receiver's connected server. wait_event will identify the specific wait point. The server process is idle. The pg_stat_activity view will have one row per server process, showing information related to the current activity of that process. Waiting for base backup to read from a file. Waiting during recovery when WAL data is not available from any source (. Waiting for I/O on an async (notify) buffer. Waiting to read or update dynamic shared memory state. (See Chapter19 for details about setting configuration parameters.). Logical decoding plugins may optionally emit tracking messages; if they do not, the tracking mechanism will simply display NULL lag. Waiting for any activity when processing replies from WAL receiver in WAL sender process. Users interested in obtaining more detailed information on PostgreSQL I/O behavior are advised to use the PostgreSQL statistics collector in combination with operating system utilities that allow insight into the kernel's handling of I/O. Host name of the connected client, as reported by a reverse DNS lookup of client_addr. Additional functions related to the cumulative statistics system are listed in Table28.34. Waiting for a write of mapping data during a logical rewrite. Waiting for background worker to shut down. For client backends, this is the time the client connected to the server. What we have discussed in this episode of 5mins of Postgres. Pointers to free buffers and to the next victim are protected by one buffer strategy lock spinlock. Waiting to read or update transaction commit timestamps. You Waiting for data to reach durable storage while creating the data directory lock file. pg_stat_reset_single_function_counters ( oid ) void. Waiting for a write to update the control file. Waiting for logical rewrite mappings to reach durable storage during a checkpoint. Waiting to read or update background worker state. Waiting for a WAL file to reach durable storage. Its 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. Cumulative statistics are collected in shared memory. These access functions use a backend ID number, which ranges from one to the number of currently active backends. See, Only one row, showing statistics about the WAL receiver from that receiver's connected server. Waiting for a read from a relation data file. The functions for per-function statistics take a function OID. Waiting for a write of a two phase state file. The wait_event and state columns are independent. Waiting for an asynchronous prefetch from a relation data file. Waiting for the termination of another backend. Waiting to read or update old snapshot control information. Waiting for a write when creating a new WAL segment by copying an existing one. Number of deadlocks detected in this database. 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. Waiting for WAL to reach durable storage during bootstrapping. Waiting in main loop of checkpointer process. Waiting to read or update the control file or creation of a new WAL file. See, One row for each tracked function, showing statistics about executions of that function. Waiting to read or update vacuum-related information for a B-tree index. 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 for a read when creating a new WAL segment by copying an existing one. Waiting for an immediate synchronization of a relation data file to durable storage. idle: The backend is waiting for a new client command. The pg_stat_activity view will have one row per server process, showing information related to the current activity of that process. Waiting for background worker to shut down. It can be joined to pg_stat_activity or pg_stat_replication on the pid column to get more details about the connection. See, Only one row, showing statistics about the WAL receiver from that receiver's connected server. Resets statistics of the replication slot defined by the argument. The track_functions parameter controls exactly which functions are tracked. 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, last_msg_send_time timestamp with time zone, Send time of last message received from origin WAL sender, last_msg_receipt_time timestamp with time zone, 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, Host of the PostgreSQL instance this WAL receiver is connected to. See, One row per WAL sender process, showing statistics about replication to that sender's connected standby server. Waiting for WAL to be flushed in WAL sender process. this form checksum_last_failure timestamp with time zone. 214 . Waiting to read or update replication slot state. If you've got a moment, please tell us what we did right so we can do more of it. Alone the requirement of separate fsyncs and everything is pretty bothersome. The argument can be one of CommitTs, MultiXactMember, MultiXactOffset, Notify, Serial, Subtrans, or Xact to reset the counters for only that entry. Waiting for stats dynamic shared memory allocator access, Waiting for stats shared memory hash table access, Waiting for shared memory stats data access. PostgreSQL utilizes lightweight locks (LWLocks) to synchronize and control access to the buffer content. I've made . Process ID of the parallel group leader, if this process is a parallel query worker. 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. 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 to allocate or free a replication slot. Statistics Collection Configuration, One row per server process, showing information related to the current activity of that process, such as state and current query. Postgres Source Code Docs: Locking Overview. Waiting for a write of mapping data during a logical rewrite. This category is useful for modules to track custom waiting points. You can split your Wait event name if backend is currently waiting, otherwise NULL. 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 replace a page in WAL buffers. 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. See. Total amount of data written to temporary files by queries in this database. See, One row per connection (regular and replication), showing information about GSSAPI authentication and encryption used on this connection. Waiting in background writer process, hibernating. This can be used to gauge the delay that synchronous_commit level on incurred while committing if this server was configured as a synchronous standby. Waiting to read or update the state of prepared transactions. being read from storage. Note that this includes data that is streamed and/or spilled. Current WAL sender state. Waiting to read while creating the data directory lock file. Waiting for an elected Parallel Hash participant to finish allocating more buckets. If a backend is in the active state, it may or may not be waiting on some event. fastpath function call: The backend is executing a fast-path function. Waiting to send bytes to a shared message queue. 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 a barrier event to be processed by all backends. Javascript is disabled or is unavailable in your browser. This is used by system processes waiting for activity in their main processing loop. Waiting for a write of a timeline history file received via streaming replication. See, One row for each sequence in the current database, showing statistics about I/O on that specific sequence. If the standby server has entirely caught up with the sending server and there is no more WAL activity, the most recently measured lag times will continue to be displayed for a short time and then show NULL. Topics Relevant engine versions Context Causes Actions Relevant engine versions Waiting for I/O on a multixact offset SLRU buffer. Waiting for a relation data file to reach durable storage. 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. The server process is waiting for some condition defined by an extension module. These times represent the commit delay that was (or would have been) introduced by each synchronous commit level, if the remote server was configured as a synchronous standby. Activity: The server process is idle. Waiting to get the start location of a scan on a table for synchronized scans. Waiting for a write during reorder buffer management. Waiting to ensure that the table it has selected for a vacuum still needs vacuuming. 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.