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The server process is waiting for some condition defined by an extension module. The pg_stat_archiver view will always have a single row, containing data about the archiver process of the cluster. Waiting for the group leader to update transaction status at end of a parallel operation. Detailed Description . Waiting to apply WAL at recovery because it is delayed. The parameter track_counts controls whether statistics are collected about table and index accesses. Waiting for data to reach durable storage while assigning WAL sync method. Waiting for a read while adding a line to the data directory lock file. Waiting in background writer process, hibernating. A backend process is waiting to associate a data block with a buffer in the shared buffer pool. Additional Statistics Functions. 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. Number of temporary files created by queries in this database. pg_stat_get_backend_pid ( integer ) integer, pg_stat_get_backend_start ( integer ) timestamp with time zone. Returns the set of currently active backend ID numbers (from 1 to the number of active backends). Waiting for a read during recheck of the data directory lock file. Waiting for logical rewrite mappings to reach durable storage. replication_origin: Waiting to read or update the replication progress. 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. Several predefined views, listed in Table28.1, are available to show the current state of the system. 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. Returns the OID of the database this backend is connected to. 39919 LWLock buffer_mapping 5119 Client ClientRead 3116 IO DataFileRead . Total number of WAL full page images generated, Number of times WAL data was written to disk because WAL buffers became full. Waiting for data to reach durable storage while adding a line to the data directory lock file. Waiting for another process to be attached to a shared message queue. See, One row for each index in the current database, showing statistics about accesses to that specific index. Current overall state of this backend. (See Chapter19 for details about setting configuration parameters.). postgres 26 Heap_Insert The parameter track_functions enables tracking of usage of user-defined functions. 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. This is consistent with the goal of measuring synchronous commit and transaction visibility delays for recent write transactions. Waiting for a write while initializing a new WAL 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. Last write-ahead log location already received and written to disk, but not flushed. Returns the time when the backend's most recent query was started. Waiting for base backup to read from a file. Waiting in main loop of checkpointer process. proc: Waiting to read or update the fast-path lock information. Waiting for a logical replication remote server to send data for initial table synchronization. Waiting for background worker to shut down. 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. When a buffer is read from disk (or written to disk), an IO in progress lock is also acquired, which indicates to other processes that the page is being read (or written) they can queue up if they need to do something with this page. Postgres Locking: When is it Concerning? Waiting for a write to the relation map file. postgres/README at master postgres/postgres GitHub buffer_io: Waiting for I/O on a data page. See, One row per connection (regular and replication), showing information about SSL used on this connection. . Waiting to elect a Parallel Hash participant to allocate a hash table. The most possible reason for why you see LWLockTranche/buffer_mapping Waiting for the relation map file to reach durable storage. Waiting for data to reach durable storage while creating the data directory lock file. Current WAL sender state. 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. In some cases, the name assigned by an extension will not be available in all server processes; so an LWLock wait event might be reported as just extension rather than the extension-assigned name. A process acquires an LWLock in a shared mode to read from the buffer and an exclusive mode to write to the buffer. OID of the database this backend is connected to, Name of the database this backend is connected to. Waiting in main loop of startup process for WAL to arrive, during streaming recovery. This function is restricted to superusers by default, but other users can be granted EXECUTE to run the function. This is used by system processes waiting for activity in their main processing loop. (Conflicts occur only on standby servers; see, Number of temporary files created by queries in this database. LWLock:buffer_mapping. Distinguished Name (DN) field from the client certificate used, or NULL if no client certificate was supplied or if SSL is not in use on this connection. Time elapsed between flushing recent WAL locally and receiving notification that this standby server has written, flushed and applied it. Streaming only works with top-level transactions (subtransactions can't be streamed independently), so the counter is not incremented for subtransactions. BufferPin: The server process is waiting to access to a data buffer during a period when no other process can be examining that buffer. Waiting for the group leader to clear the transaction ID at end of a parallel operation. Thanks for letting us know this page needs work. Increase the number of wal_buffers available to the database. The per-index statistics are particularly useful to determine which indexes are being used and how effective they are. See Table28.5 through Table28.13. pg_stat_get_backend_xact_start ( integer ) timestamp with time zone. finish their input/output (I/O) operations when concurrently trying to access a page. For example, to show the PIDs and current queries of all backends: Table28.20. Waiting to read or update information about. Waiting to read or update replication slot state. Waiting to read or update a process' fast-path lock information. Waiting for a newly initialized WAL file to reach durable storage. Waiting to associate a data block with a buffer in the buffer pool. 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 to add a message in shared invalidation queue. 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. (Conflicts occur only on standby servers; see pg_stat_database_conflicts for details.). Waiting for a read when creating a new WAL segment by copying an existing one. Waiting for recovery conflict resolution for dropping a tablespace. 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 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 read from the control file. Waiting for a two phase state file to reach durable storage. See, One row per database, showing database-wide statistics about query cancels due to conflict with recovery on standby servers. sync: This standby server is synchronous. The parameter track_activities enables monitoring of the current command being executed by any server process. Doing this helps Waiting in main loop of WAL sender process. This should not be used for data integrity checks. Waiting to read or update shared multixact state. Waiting to allocate or assign a transaction id. Extensions can add LWLock types to the list shown in Table28.12. LWLock:BufferIO. What we have discussed in this episode of 5mins of Postgres. See, At least one row per subscription, showing information about the subscription workers. Since collection of statistics adds some overhead to query execution, the system can be configured to collect or not collect information. Waiting to acquire a speculative insertion lock. query performance - PostgreSQL LWLock: lock_manager issue - Database Waiting to access the multixact member SLRU cache. BK_1935: "IObuffer_locks,ControlLock()"IOControlLockControlLockIOSlruSharedData. Waiting to read or update the state of logical replication workers. If a backend is in the active state, it may or may not be waiting on some event. Each individual server process flushes out accumulated statistics to shared memory just before going idle, but not more frequently than once per PGSTAT_MIN_INTERVAL milliseconds (1 second unless altered while building the server); so a query or transaction still in progress does not affect the displayed totals and the displayed information lags behind actual activity. number of buffers needed by the current workload, The size of the shared buffer pool not being well balanced with the number of pages being evicted by other 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. Process ID of the parallel group leader, if this process is a parallel query worker. The server process is waiting for some interaction with another server process. Using pg_stat_reset() also resets counters that autovacuum uses to determine when to trigger a vacuum or an analyze. Type of current backend. Postgres 10.3: SELECT queries hang for hours - Stack Overflow The statistics collector transmits the collected information to other PostgreSQL processes through temporary files. Waiting to access the list of predicate locks held by serializable transactions. The server process is waiting for a lightweight lock. However, current-query information collected by track_activities is always up-to-date. Waiting for parallel query dynamic shared memory allocation lock. 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. Returns the time when this process was started. Current overall state of this backend. Such a system would show similar times while new WAL is being generated, but would differ when the sender becomes idle. The combination of certificate serial number and certificate issuer uniquely identifies a certificate (unless the issuer erroneously reuses serial numbers). Waiting for SSL while attempting connection. being read from storage. Waiting for other Parallel Hash participants to finish repartitioning. If the argument is NULL, resets statistics for all the replication slots. See Table28.5 through Table28.13. pg_stat_get_backend_wait_event_type ( integer ) text. Table28.6. Waiting in main loop of checkpointer process. 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. Waiting for a read during reorder buffer management. Waiting in WAL receiver to receive data from remote server. For more information on lightweight locks, see Locking Overview. Waiting for a write to a relation data file. Java_Java_File_Io_Buffer - Resets statistics for a single function in the current database to zero. It can be joined to pg_stat_activity or pg_stat_replication on the pid column to get more details about the connection. See, One row only, showing statistics about the background writer process's activity. This is consistent with the goal of measuring synchronous commit and transaction visibility delays for recent write transactions. 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. LWLock: The backend is waiting for a lightweight lock. Number of deadlocks detected in this database. Waiting to access the shared per-process data structures (typically, to get a snapshot or report a session's transaction ID). David Christensen on Twitter. Waiting to access the sub-transaction SLRU cache. Waiting to read or update shared notification state. 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. All temporary files are counted, regardless of why the temporary file was created, and regardless of the log_temp_files setting. See, Time when the current transaction was started. This counter is incremented each time a transaction is streamed, and the same transaction may be streamed multiple times. Waiting for background worker to shut down. LWTRANCHE_BUFFER_CONTENT @ LWTRANCHE_BUFFER_CONTENT. 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. Number of transactions spilled to disk once the memory used by logical decoding to decode changes from WAL has exceeded logical_decoding_work_mem. The access functions for per-database statistics take a database OID as an argument to identify which database to report on. Waiting to acquire a speculative insertion lock. Waiting for I/O on a commit timestamp SLRU buffer. Use partitioned tables (which also have partitioned indexes). See, One row per database, showing database-wide statistics. pg_stat_get_backend_activity_start ( integer ) timestamp with time zone. This can be used to gauge the delay that. Waiting for parallel workers to finish computing. See. pg_stat_get_backend_client_port ( integer ) integer. For client backends, this is the time the client connected to the server. Waiting for a read from a replication slot control file. Waiting for a read from a relation data file. Waiting for a read when creating a new WAL segment by copying an existing one. 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. 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, Process ID of a backend or WAL sender process, Version of SSL in use, or NULL if SSL is not in use on this connection, Name of SSL cipher in use, or NULL if SSL is not in use on this connection, Number of bits in the encryption algorithm used, or NULL if SSL is not used on this connection, True if SSL compression is in use, false if not, or NULL if SSL is not in use on this connection, Distinguished Name (DN) field from the client certificate used, or NULL if no client certificate was supplied or if SSL is not in use on this connection. See, One row per database, showing database-wide statistics. The server process is waiting for exclusive access to a data buffer. 105 #define BUFFER_MAPPING_LWLOCK_OFFSET NUM_INDIVIDUAL_LWLOCKS. Table28.17.pg_statio_all_sequences View. PostgreSQL utilizes lightweight locks (LWLocks) to synchronize and control access to the buffer content. The argument can be one of CommitTs, MultiXactMember, MultiXactOffset, Notify, Serial, Subtrans, or Xact to reset the counters for only that entry. The management of the buffers in PostgreSQL consists of a buffer descriptor that contains metadata about the buffer and the buffer content that is read from the disk. It can be joined to pg_stat_activity or pg_stat_replication on the pid column to get more details about the connection. Waiting to acquire a virtual transaction ID lock. Waiting to update limits on transaction id and multixact consumption. Returns the OID of the user logged into this backend. Waiting to access the serializable transaction conflict SLRU cache. Waiting for a read during reorder buffer management. Some of the information in the dynamic statistics views shown in Table28.1 is security restricted. The track_functions parameter controls exactly which functions are tracked. Waiting for a write of a WAL page during bootstrapping. If state is active this field shows the identifier of the currently executing query.