For an asynchronous standby, the replay_lag column approximates the delay before recent transactions became visible to queries. The pg_stat_archiver view will always have a single row, containing data about the archiver process of the cluster. However, they are also used to ensure mutual exclusion for certain internal operations such as relation extension. 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 read or update multixact member mappings. This is used by system processes waiting for activity in their main processing loop. idle: The backend is waiting for a new client command. Synchronous state of this standby server. From pg_stat_activity i noticed that the wait_event_type and wait_event of these queries is as follows: If a backend is in the active state, it may or may not be waiting on some event. Waiting for another process to be attached to a shared message queue. Logical decoding plugins may optionally emit tracking messages; if they do not, the tracking mechanism will simply display NULL lag. PostgreSQL Entangled in Locks: Attempts to free it - Amit Kapila - Dilip Kumar PGCon 2017 . purpose is for the same page to be read into the shared buffer. Waiting to access the list of predicate locks held by the current serializable transaction during a parallel query. postgres 26 Heap_Insert Waiting to read or truncate multixact information. Waiting to read while creating the data directory lock file. 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). Waiting for other process to be attached in shared message queue. 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. to keep index reordering low and reduces its impact. Each such lock protects a particular data structure in shared memory. The track_functions parameter controls exactly which functions are tracked. 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 for a write of a timeline history file received via streaming replication. Returns the process ID of the server process attached to the current session. Waiting for a relation data file to be truncated. Occasionally i noticed that in random interval of times the dbms become slow and get stuck on a few SELECT queries. The server process is waiting for some interaction with another server process. Waits for a buffer pin ( BufferPin ). Waiting to update limits on transaction id and multixact consumption. Prevent sudden database connection spikes by using a connection pool. For details such as the functions' names, consult the definitions of the standard views. This is consistent with the goal of measuring synchronous commit and transaction visibility delays for recent write transactions. 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. 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. Alone the requirement of separate fsyncs and everything is pretty bothersome. The server process is waiting for a lightweight lock. 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. Total number of WAL full page images generated, Number of times WAL data was written to disk because WAL buffers became full. Its purpose is for the same page to be read into the shared buffer. Waiting to manage an extension's space allocation in shared memory. Waiting to update the relation map file used to store catalog to filenode mapping. pg_stat_get_backend_client_addr ( integer ) inet. 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 read or update the progress of one replication origin. Waiting for a newly initialized WAL file to reach durable storage. The pg_statio_all_indexes view will contain one row for each index in the current database, showing statistics about I/O on that specific index. Waiting for the relation map file to reach durable storage. Waiting for a write of a WAL page during bootstrapping. Waiting for other Parallel Hash participants to finish loading a hash table. Waiting in main loop of WAL sender process. This view will only contain information on standby servers, since conflicts do not occur on master servers. The parameter track_counts controls whether cumulative statistics are collected about table and index accesses. PostgreSQL 's statistics collector is a subsystem that supports collection and reporting of information about server activity. might be causing it. 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. Waiting for WAL to reach durable storage during bootstrapping. Waiting for a write while creating the data directory lock file. PostgreSQL's statistics collector is a subsystem that supports collection and reporting of information about server activity. Waiting for a write while creating the data directory lock file. I'd like to know more about what these locks could imply if anything. Waiting for a serialized historical catalog snapshot to reach durable storage. Waiting to elect a Parallel Hash participant to allocate the initial hash table. 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. Time elapsed between flushing recent WAL locally and receiving notification that this standby server has written and flushed it (but not yet applied it). See, One row per database, showing database-wide statistics. The parameter track_wal_io_timing enables monitoring of WAL write times. Note that this includes the transactions that are streamed and/or spilled. Waiting for a write to a relation data file. 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. The pg_stat_user_functions view will contain one row for each tracked function, showing statistics about executions of that function. This can be used to gauge the delay that. BufferCacheHitRatio and LWLock:BufferIO wait . Resets statistics to zero for a single SLRU cache, or for all SLRUs in the cluster. Host name of the connected client, as reported by a reverse DNS lookup of client_addr. See, Only one row, showing statistics about blocks prefetched during recovery. pg_stat_reset_subscription_stats ( oid ) void. Waiting for a newly created timeline history file to reach durable storage. Serial number of the client certificate, or NULL if no client certificate was supplied or if SSL is not in use on this connection. 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. Waiting to manage space allocation in shared memory. Waiting for a relation data file to be extended. Waiting for a write when creating a new WAL segment by copying an existing one. Waiting for data to reach durable storage while assigning a new WAL sync method. 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. For tranches registered by extensions, the name is specified by extension and this will be displayed as wait_event. Waiting to allocate or free a replication slot. Waiting for an elected Parallel Hash participant to allocate more batches. Waiting to read or update vacuum-related information for a B-tree index. Waiting in main loop of background writer process. Waiting to acquire a lock on a page of a relation. Waiting for I/O on a sub-transaction SLRU buffer. Last write-ahead log location already received and written to disk, but not flushed. After v9.5, the buffer cache is protected by 128 hash tables each protected by a LWLock. Waiting for I/O on a multixact offset SLRU buffer. However, current-query information collected by track_activities is always up-to-date. When analyzing statistics interactively, or with expensive queries, the time delta between accesses to individual statistics can lead to significant skew in the cached statistics. 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. 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. checksum_last_failure timestamp with time zone. So the statistics will show static information as long as you continue the current transaction. Waiting to apply WAL during recovery because of a delay setting. Waiting for other Parallel Hash participants to finish partitioning the outer relation. Waiting to get the start location of a scan on a table for synchronized scans. Wait event name if backend is currently waiting, otherwise NULL. 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. Superusers and roles with privileges of built-in role pg_read_all_stats (see also Section22.5) can see all the information about all sessions. fastpath function call: The backend is executing a fast-path function. quorum: This standby server is considered as a candidate for quorum standbys. 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. 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. Waiting to associate a data block with a buffer in the buffer pool. The functions for per-function statistics take a function OID. Waiting to write a protocol message to a shared message queue. The function pg_stat_get_backend_idset provides a convenient way to generate one row for each active backend for invoking these functions. See. Pointers to free buffers and to the next victim are protected by one buffer strategy lock spinlock. 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. Using pg_stat_reset() also resets counters that autovacuum uses to determine when to trigger a vacuum or an analyze. a page) has to be retrieved outside the shared buffer pool. Waiting for a read while adding a line to the data directory lock file. Sometimes it may be more convenient to obtain just a subset of this information. Number of times WAL buffers were written out to disk via XLogWrite request.