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This field is truncated like client_dn. Waiting for a write to a relation data file. Waiting for background worker to shut down. Waiting for confirmation from remote server during synchronous replication. lock_manager See, One row for each tracked function, showing statistics about executions of that function. 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. 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. Waiting to receive bytes from a shared message queue. Using pg_stat_reset() also resets counters that autovacuum uses to determine when to trigger a vacuum or an analyze. Waiting to read or write relation cache initialization file. 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. Waiting for a write to a replication slot control file. Waiting in main loop of background writer process. to keep index reordering low and reduces its impact. Waiting a new WAL segment created by copying an existing one to reach durable storage. pg_stat_get_backend_client_port ( integer ) integer. Also, the collector itself emits a new report at most once per PGSTAT_STAT_INTERVAL milliseconds (500 ms unless altered while building the server). Waiting for data to reach durable storage while creating the data directory lock file. Waiting to retrieve or remove messages from shared invalidation queue. Waiting to update limits on transaction id and multixact consumption. This and other streaming counters for this slot can be used to tune logical_decoding_work_mem. 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. 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. Waiting for a relation data file to be extended. Resets statistics to zero for a single SLRU cache, or for all SLRUs in the cluster. Therefore, while holding an exclusive lock, a process prevents other processes from acquiring a shared or exclusive lock. Number of scheduled checkpoints that have been performed, Number of requested checkpoints that have been performed, Total amount of time that has been spent in the portion of checkpoint processing where files are written to disk, in milliseconds, Total amount of time that has been spent in the portion of checkpoint processing where files are synchronized to disk, in milliseconds, Number of buffers written during checkpoints, Number of buffers written by the background writer, Number of times the background writer stopped a cleaning scan because it had written too many buffers, Number of buffers written directly by a backend, Number of times a backend had to execute its own fsync call (normally the background writer handles those even when the backend does its own write). replication_slot_io: Waiting for I/O on a replication slot. Waiting for a write of a timeline history file received via streaming replication. 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, Estimated number of rows inserted since this table was last vacuumed, Last time at which this table was manually vacuumed (not counting VACUUM FULL), Last time at which this table was vacuumed by the autovacuum daemon, Last time at which this table was manually analyzed, last_autoanalyze timestamp with time zone, Last time at which this table was analyzed by the autovacuum daemon, Number of times this table has been manually vacuumed (not counting VACUUM FULL), 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. This block has to be read from outside the shared buffer pool, defined by the The server process is waiting for an I/O operation to complete. Waiting for a write of a newly created timeline history file. Its purpose is for the same page to be read into the shared buffer. See, One row only, showing statistics about WAL activity. (For example, in psql you could issue \d+ pg_stat_activity.) If the argument is NULL, resets statistics for all the replication slots. Waiting for an elected Parallel Hash participant to allocate more batches. If a backend is in the active state, it may or may not be waiting on some event. See, At least one row per subscription, showing information about the subscription workers. Waiting for a read of a timeline history file. Waiting for a read of the relation map file. pg_stat_get_activity, the underlying function of the pg_stat_activity view, returns a set of records containing all the available information about each backend process. Conversely, if it's known that statistics are only accessed once, caching accessed statistics is unnecessary and can be avoided by setting stats_fetch_consistency to none. Waiting in main loop of background writer process background worker. Waiting for the relation map file to reach durable storage. 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. Lag times work automatically for physical replication. The server process is waiting for activity on a socket connected to a user application. See, Only one row, showing statistics about the WAL receiver from that receiver's connected server. You can invoke pg_stat_clear_snapshot() to discard the current transaction's statistics snapshot or cached values (if any). Waiting to read or update multixact offset mappings. Waiting to acquire an advisory user lock. Last write-ahead log location sent on this connection, Last write-ahead log location written to disk by this standby server, Last write-ahead log location flushed to disk by this standby server, Last write-ahead log location replayed into the database on this standby server. Waiting to read or update dynamic shared memory allocation information. Waiting in main loop of WAL writer process. Waiting for startup process to send initial data for streaming replication. 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 I/O on a sub-transaction SLRU buffer. Waiting for a replication slot control file to reach durable storage. See, One row per connection (regular and replication), showing information about SSL used on this connection. 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. Before PostgreSQL 8.1, all operations of the shared buffer manager itself were protected by a single system-wide lock, the BufMgrLock, which unsurprisingly proved to be a source of contention. Waiting for a write of a WAL page during bootstrapping. Waiting for WAL buffers to be written to disk. Waiting for a read of a two phase state file. TCP port number that the client is using for communication with this backend, or -1 if a Unix socket is used. Waiting for background worker to start up. Time when the currently active query was started, or if state is not active, when the last query was started. . Waiting during base backup when throttling activity. Waiting to access the commit timestamp SLRU cache. (See Chapter20 for details about setting configuration parameters.). Waiting for a write while adding a line to the data directory lock file. Waiting for recovery conflict resolution for a vacuum cleanup. There have been several occasions when a query is being executed dozens of times simultaneously by one or many users. Waiting for a replication slot control file to reach durable storage. But processes can also await other events: Waits for input/output ( IO) occur when a process needs to read or write data. 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. 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. In order to write the disk block into buffer memory, the buffer cache's hash table entry needs updating. IO: The server process is waiting for a IO to complete. 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 to the relation map file. Waiting for I/O on a clog (transaction status) buffer. A process can wait for the data needed from a client ( Client) or another process ( IPC ). Waiting for a read during reorder buffer management. Returns the time when the backend's current transaction was started. Heavyweight locks, also known as lock manager locks or simply locks, primarily protect SQL-visible objects such as tables. Waiting for the group leader to update transaction status at end of a parallel operation. Each such lock protects a particular data structure in shared memory. Last write-ahead log location already received and written to disk, but not flushed. Waiting to create, drop or use a replication origin. Waiting to elect a Parallel Hash participant to allocate more buckets. Postgres Source Code Docs: Locking Overview. pg_stat_get_backend_wait_event_type ( integer ) text. The statistics collector transmits the collected information to other PostgreSQL processes through temporary files. 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 read or write a data page in memory. Waiting for I/O on a multixact member SLRU buffer. See Section30.5 for more information about the internal WAL function issue_xlog_fsync. IPC: The server process is waiting for some activity from another process in the server. Some of the information in the dynamic statistics views shown in Table28.1 is security restricted. See, One row per WAL sender process, showing statistics about replication to that sender's connected standby server. Additional functions related to the cumulative statistics system are listed in Table28.34. Connection string used by this WAL receiver, with security-sensitive fields obfuscated. Returns the text of this backend's most recent query. This should not be used for data integrity checks. The overhead of a file is much more than wasting the remainder of a page. The wait_event and state columns are independent. quorum: This standby server is considered as a candidate for quorum standbys. Waiting in background writer process, hibernating. - 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 Waiting to access a shared tuple store during parallel query. to report a documentation issue. Waiting for WAL to reach durable storage during bootstrapping. Waiting for any activity when processing replies from WAL receiver in WAL sender process. The pg_stat_user_functions view will contain one row for each tracked function, showing statistics about executions of that function. Returns the wait event type name if this backend is currently waiting, otherwise NULL. Note that this includes data that is streamed and/or spilled. Waiting for confirmation from a remote server during synchronous replication. pg_blocking_pids function. Waiting to read or update the state of logical replication workers. Waiting for a write of a two phase state file. 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. See, One row per WAL sender process, showing statistics about replication to that sender's connected standby server. The server process is waiting for some interaction with another server process. 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. Waiting for I/O on a multixact offset SLRU buffer. Waits for lightweight locks ( LWLock ). When recovery is performed at server start (e.g., after immediate shutdown, server crash, and point-in-time recovery), all statistics counters are reset. Waiting for a timeline history file received via streaming replication to reach durable storage. LWLock: The backend is waiting for a lightweight lock. Waiting to read while creating the data directory lock file. Then identify which query Other ways of looking at the statistics can be set up by writing queries that use the same underlying statistics access functions used by the standard views shown above. (The path case can be distinguished because it will always be an absolute path, beginning with /.). The access functions for per-database statistics take a database OID as an argument to identify which database to report on. Timeout: The server process is waiting for a timeout to expire. The per-table and per-index functions take a table or index OID. Returns the time when this process was started. A database-wide ANALYZE is recommended after the statistics have been reset. Waiting for a read when creating a new WAL segment by copying an existing one. Waiting for a newly initialized WAL file to reach durable storage. The pg_stat_activity view will have one row per server process, showing information related to the current activity of that process. These numbers do not act as stated above; instead they update continuously throughout the transaction. 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. Possible values are: active: The backend is executing a query. 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. Waiting for an asynchronous prefetch from a relation data file. 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. Table28.31.pg_statio_all_sequences View, Number of disk blocks read from this sequence. Waiting to get a snapshot or clearing a transaction id at transaction end. Number of times transactions were spilled to disk while decoding changes from WAL for this slot. This counts top-level transactions only, and is not incremented for subtransactions. 214 . Waiting in main loop of logical replication launcher process. Total amount of data written to temporary files by queries in this database. The pg_stat_replication view will contain one row per WAL sender process, showing statistics about replication to that sender's connected standby server. This is consistent with the goal of measuring synchronous commit and transaction visibility delays for recent write transactions. 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. 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 update the relation map file used to store catalog to filenode mapping. Table28.6. Presently, the collector can count accesses to tables and indexes in both disk-block and individual-row terms. If you see anything in the documentation that is not correct, does not match Waiting for a read of a serialized historical catalog snapshot. See Section30.5 for more information about the internal WAL function XLogWrite. Such a system would show similar times while new WAL is being generated, but would differ when the sender becomes idle. 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. For tranches registered by extensions, the name is specified by extension and this will be displayed as wait_event. Waiting to access the sub-transaction SLRU cache. Each buffer header also contains an LWLock, the "buffer content lock", that *does* represent the right to access the data: in the buffer. Waiting in main loop of WAL sender process. Waiting for a replication slot to become inactive so it can be dropped. might be causing it. pg_stat_get_activity, the underlying function of the pg_stat_activity view, returns a set of records containing all the available information about each backend process. Pointers to free buffers and to the next victim are protected by one buffer strategy lock spinlock. The track_functions parameter controls exactly which functions are tracked. Waiting to send bytes to a shared message queue. Waiting to access a parallel query's information about type modifiers that identify anonymous record types. 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. Resetting these counters can cause autovacuum to not perform necessary work, which can cause problems such as table bloat or out-dated table statistics. Waiting for a read from a replication slot control file. Waiting to read or update the last value set for a transaction commit timestamp. This counter is incremented each time a transaction is spilled, and the same transaction may be spilled multiple times. The parameter track_wal_io_timing enables monitoring of WAL write times. See, One row per connection (regular and replication), showing information about SSL used on this connection. Current overall state of this backend. Time when this process was started. Principal used to authenticate this connection, or NULL if GSSAPI was not used to authenticate this connection. 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. In all other states, it shows the last query that was executed. Waiting to access the list of finished serializable transactions. Waiting in main loop of WAL sender process. Waiting in main loop of checkpointer process. See, One row for each index in the current database, showing statistics about I/O on that specific index. async: This standby server is asynchronous. Waiting for I/O on commit timestamp buffer. If the argument is NULL, reset statistics for all subscriptions. Waiting for an elected Parallel Hash participant to allocate a hash table. wait_event will identify the specific wait point. Most such locks protect a particular data structure in shared memory. 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.