Please refer to your browser's Help pages for instructions. Waiting to access the transaction status SLRU cache. Time when this process' current transaction was started, or null if no transaction is active. Waiting for the group leader to clear the transaction ID at end of a parallel operation. The generated IO patterns are also much worse. Number of transactions spilled to disk once the memory used by logical decoding to decode changes from WAL has exceeded logical_decoding_work_mem. Waiting for SLRU data to reach durable storage following a page write. Number of disk blocks read from this index. Extensions can add LWLock types to the list shown in Table28.12. Timeout: The server process is waiting for a timeout to expire. The LWLock:BufferIO wait event precedes the IO:DataFileRead wait event. See. From the Actions drop-down menu, choose Create Read Replica. Waiting for a buffered file to be truncated. Aurora PostgreSQL wait events - Amazon Aurora Waiting when WAL data is not available from any kind of sources (local, archive or stream) before trying again to retrieve WAL data, at recovery. The WALWriteLock wait occurs while PostgreSQL flushes WAL records to disk or during a WAL segment switch.. How to reduce this wait . Thus, the server expects something to happen that is independent of its internal processes. Waiting for a write to the relation map file. wait_event will identify the specific wait point. Waiting while sending synchronization requests to the checkpointer, because the request queue is full. 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. Waiting for truncate of mapping data during a logical rewrite. See, One row for each backend (including autovacuum worker processes) running, One row only, showing statistics about the WAL archiver process's activity. For client backends, this is the time the client connected to the server. Postgres Locking: When is it Concerning? This view will only contain information on standby servers, since conflicts do not occur on primary servers. Waiting for a write while creating the data directory lock file. Autovacuum worker or launcher waiting to update or read the current state of autovacuum workers. Waiting to elect a Parallel Hash participant to allocate a hash table. Waiting for background worker to start up. Topics Relevant engine versions Context Causes Actions Relevant engine versions Waiting to read or update sub-transaction information. You can invoke pg_stat_clear_snapshot() to discard the current transaction's statistics snapshot or cached values (if any). 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. This function is restricted to superusers by default, but other users can be granted EXECUTE to run the function. The counter gets incremented for both top-level transactions and subtransactions. Waiting to read or update the replication progress. The pg_statio_user_tables and pg_statio_sys_tables views contain the same information, but filtered to only show user and system tables respectively. A backend process wants to read a page into shared memory. If this field is null, it indicates that this is an internal server process. 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. idle in transaction: The backend is in a transaction, but is not currently executing a query. gorthx on Twitter Waiting for a write of a newly created timeline history file. Waiting for changes to a relation data file to reach durable storage. Waiting to access a parallel query's information about type modifiers that identify anonymous record types. For example, to show the PIDs and current queries of all backends: Table28.20. Waiting for a write of a two phase state file. Waiting to receive bytes from a shared message queue. Waiting for I/O on a commit timestamp SLRU buffer. 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. For client backends, this is the time the client connected to the server. Waiting to read or update the progress of one replication origin. A transaction can also see its own statistics (as yet untransmitted to the collector) in the views pg_stat_xact_all_tables, pg_stat_xact_sys_tables, pg_stat_xact_user_tables, and pg_stat_xact_user_functions. Therefore, while holding an exclusive lock, a process prevents other processes from acquiring a shared or exclusive lock. If the current query is the first of its transaction, this column is equal to the query_start column. Re: Improve WALRead() to suck data directly from WAL buffers when possible - Mailing list pgsql-hackers See, One row per subscription, showing statistics about errors. wait_event will identify the type of lock awaited. Waiting for a write to a replication slot control file. Waiting for a timeline history file received via streaming replication to reach durable storage. 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. Waiting in main loop of logical apply process. Re: Improve WALRead() to suck data directly from WAL buffers when Waiting for a write during a file copy operation. Waiting to receive bytes from a shared message queue. The LWLock:BufferIO event occurs when Aurora PostgreSQL or RDS for PostgreSQL is waiting for other processes to Waiting for a replication origin to become inactive so it can be dropped. 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 WAL to be flushed in WAL sender process. This is controlled by configuration parameters that are normally set in postgresql.conf. 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. For details such as the functions' names, consult the definitions of the standard views. Waiting for a read of a serialized historical catalog snapshot. Waiting to read or update dynamic shared memory state. Waiting for WAL to reach durable storage during bootstrapping. 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. PostgreSQL Source Code: src/include/storage/lwlock.h Source File OID of the database this backend is connected to, Name of the database this backend is connected to. The track_functions parameter controls exactly which functions are tracked. Waiting to replace a page in WAL buffers. From pg_stat_activity i noticed that the wait_event_type and wait_event of these queries is as follows: When the buffer manager receives a request, PostgreSQL uses the buffer_tag of the desired page. Waiting to read or update multixact member mappings. This category is useful for modules to track custom waiting points. See Table28.5 through Table28.13. Waiting for a write of logical rewrite mappings. See, One row per database, showing database-wide statistics. Postgres Source Code Docs: Locking Overview. Waiting to read or truncate multixact information. Waiting for a relation data file to be truncated. Waiting for group leader to clear transaction id at transaction end. Waiting for activity from a child process while executing a. The pg_stat_replication_slots view will contain one row per logical replication slot, showing statistics about its usage. These numbers do not act as stated above; instead they update continuously throughout the transaction. 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. The pg_stat_user_functions view will contain one row for each tracked function, showing statistics about executions of that function. pg_stat_reset_replication_slot ( text ) void. 213 * Prior to PostgreSQL 9.4, we used an enum type called LWLockId to refer. 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. There are also several other views, listed in Table28.2, available to show the accumulated statistics. Waiting for a write of a timeline history file received via streaming replication. See, One row for each table in the current database, showing statistics about accesses to that specific table. True if GSSAPI encryption is in use on this connection. Waiting for a logical replication remote server to change state. This has no effect in a quorum-based synchronous replication. LWLock:BufferIO - Amazon Aurora Total amount of time spent writing WAL buffers to disk via XLogWrite request, in milliseconds (if track_wal_io_timing is enabled, otherwise zero). Waiting for action on logical replication worker to finish. Waiting to read or update shared multixact state. This event type indicates a process waiting for activity in its main processing loop. Waiting to acquire a lock on a page of a relation. Waiting for the control file to reach durable storage. Waiting for a relation data file to be truncated. The per-index statistics are particularly useful to determine which indexes are being used and how effective they are. Waiting to read or update dynamic shared memory allocation information. Waiting to acquire a lock on a non-relation database object. LWLock- buffer_mapping : r/PostgreSQL - reddit.com It works like this: Table28.17.pg_statio_all_sequences View. Port number of the PostgreSQL instance this WAL receiver is connected to. This has no effect in a quorum-based synchronous replication. Returns the time when the backend's current transaction was started. The type of event for which the backend is waiting, if any; otherwise NULL. These access functions use a backend ID number, which ranges from one to the number of currently active backends. See, One row per WAL sender process, showing statistics about replication to that sender's connected standby server. Priority of this standby server for being chosen as the synchronous standby in a priority-based synchronous replication. Waiting for logical rewrite mappings to reach durable storage during a checkpoint. Waiting to create, drop or use a replication origin. Streaming only works with top-level transactions (subtransactions can't be streamed independently), so the counter is not incremented for subtransactions. Query identifiers are not computed by default so this field will be null unless compute_query_id parameter is enabled or a third-party module that computes query identifiers is configured. For an asynchronous standby, the replay_lag column approximates the delay before recent transactions became visible to queries. When using the cumulative statistics views and functions to monitor collected data, it is important to realize that the information does not update instantaneously. Waiting to insert WAL into a memory buffer. being read from storage. 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. Waiting for a read of a two phase state file. Logical decoding plugins may optionally emit tracking messages; if they do not, the tracking mechanism will simply display NULL lag. See, One row per SLRU, showing statistics of operations. We're sorry we let you down. Waiting for an immediate synchronization of a relation data file to durable storage. Thanks for letting us know we're doing a good job! Waiting to access the multixact offset SLRU cache. 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. A snapshot is taken the first time cumulative statistics are accessed in a transaction if stats_fetch_consistency is set to snapshot. IP address of the client connected to this backend.
