If the argument is other (or indeed, any unrecognized name), then the counters for all other SLRU caches, such as extension-defined caches, are reset. Waiting to access predicate lock information used by serializable transactions. 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. Extensions can register their specific waits ( Extension ). See, One row per replication slot, showing statistics about the replication slot's usage. Possible values are: Wait event name if backend is currently waiting, otherwise NULL. LWLock:buffer_mapping. This documentation is for an unsupported version of PostgreSQL. Waiting in main loop of WAL sender process. IP address of the client connected to this WAL sender. Waiting for logical rewrite mappings to reach durable storage. It can be joined to pg_stat_activity or pg_stat_replication on the pid column to get more details about the connection. pg_stat_get_activity ( integer ) setof record. Waiting for a write when creating a new WAL segment by copying an existing one. See, One row for each table in the current database, showing statistics about accesses to that specific table. pg_stat_get_backend_dbid ( integer ) oid. Waiting to read while creating the data directory lock file. Waiting to elect a Parallel Hash participant to allocate more batches. Waiting for a write of logical rewrite mappings. This function is restricted to superusers by default, but other users can be granted EXECUTE to run the function. Waiting to associate a data block with a buffer in the buffer pool. IP address of the client connected to this WAL sender. 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 a read of a timeline history file. Waiting to read or update vacuum-related information for a B-tree index. Time spent reading data file blocks by backends in this database, in milliseconds (if track_io_timing is enabled, otherwise zero), Time spent writing data file blocks by backends in this database, in milliseconds (if track_io_timing is enabled, otherwise zero), Time spent by database sessions in this database, in milliseconds (note that statistics are only updated when the state of a session changes, so if sessions have been idle for a long time, this idle time won't be included), Time spent executing SQL statements in this database, in milliseconds (this corresponds to the states active and fastpath function call in pg_stat_activity), idle_in_transaction_time double precision, Time spent idling while in a transaction in this database, in milliseconds (this corresponds to the states idle in transaction and idle in transaction (aborted) in pg_stat_activity), Total number of sessions established to this database, Number of database sessions to this database that were terminated because connection to the client was lost, Number of database sessions to this database that were terminated by fatal errors, Number of database sessions to this database that were terminated by operator intervention. idle in transaction: The backend is in a transaction, but is not currently executing a query. The per-table and per-index functions take a table or index OID. If you see anything in the documentation that is not correct, does not match Waiting to access the list of predicate locks held by the current serializable transaction during a parallel query. proc: Waiting to read or update the fast-path lock information. For details such as the functions' names, consult the definitions of the standard views. If you've got a moment, please tell us how we can make the documentation better. PostgreSQL accesses certain on-disk information via SLRU (simple least-recently-used) caches. Waiting in main loop of logical replication launcher process. 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. 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. Timeout: The server process is waiting for a timeout to expire. (For example, in psql you could issue \d+ pg_stat_activity.) OID of the database this backend is connected to, Name of the database this backend is connected to. The pg_stat_subscription view will contain one row per subscription for main worker (with null PID if the worker is not running), and additional rows for workers handling the initial data copy of the subscribed tables. There are also several other views, listed in Table28.2, available to show the accumulated statistics. Waiting to acquire an exclusive lock to truncate off any empty pages at the end of a table vacuumed. Waiting to read or update notification messages. See Section30.5 for more information about the internal WAL function issue_xlog_fsync. Waiting for SLRU data to reach durable storage following a page write. Waiting to read or truncate multixact information. When the buffer manager receives a request, PostgreSQL uses the buffer_tag of the desired page. See, One row per connection (regular and replication), showing information about GSSAPI authentication and encryption used on this connection. Waiting for a write of a two phase state file. Waiting for a write of a timeline history file received via streaming replication. Waiting for a barrier event to be processed by all backends. (To prevent ordinary users from hiding their activity from the administrator, only superusers are allowed to change these parameters with SET.). 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. This standby's xmin horizon reported by hot_standby_feedback. For client backends, this is the time the client connected to the server. Calling, Reset statistics for a single table or index in the current database to zero (requires superuser privileges by default, but EXECUTE for this function can be granted to others), Reset statistics for a single function in the current database to zero (requires superuser privileges by default, but EXECUTE for this function can be granted to others), Set of currently active backend ID numbers (from 1 to the number of active backends), Time when the most recent query was started, IP address of the client connected to this backend, TCP port number that the client is using for communication, Wait event type name if backend is currently waiting, otherwise NULL. See, Only one row, showing statistics about blocks prefetched during recovery. For an asynchronous standby, the replay_lag column approximates the delay before recent transactions became visible to queries. You can invoke pg_stat_clear_snapshot() to discard the current transaction's statistics snapshot or cached values (if any). The parameter track_io_timing enables monitoring of block read and write times. Waiting for a write of a WAL page during bootstrapping. I've made . postgres7 Slru--1. Waiting to acquire an advisory user lock. Its Waiting for a relation data file to be truncated. BufferPin: The server process is waiting to access to a data buffer during a period when no other process can be examining that buffer. BK_1935: "IObuffer_locks,ControlLock()"IOControlLockControlLockIOSlruSharedData Waiting to read or update dynamic shared memory state. Javascript is disabled or is unavailable in your browser. 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. 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 a read of a serialized historical catalog snapshot. @ LWTRANCHE_REPLICATION_SLOT_IO. Waiting for a read from a replication slot control file. 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 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 newly initialized WAL file to reach durable storage. Waiting for the termination of another backend. Time elapsed between flushing recent WAL locally and receiving notification that this standby server has written, flushed and applied it. Returns the wait event type name if this backend is currently waiting, otherwise NULL. The fields returned are a subset of those in the pg_stat_activity view. pg_stat_get_backend_activity_start ( integer ) timestamp with time zone. Waiting during base backup when throttling activity. Waiting for data to reach durable storage while creating the data directory lock file. Waiting for a read during recheck of the data directory lock file. async: This standby server is asynchronous. Waiting for a write during reorder buffer management. 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. wait_event will identify the specific wait point. Waiting for the control file to reach durable storage. Waiting for a replication origin to become inactive so it can be dropped. It is quite possible that user has registered the tranche in one of the backends (by having allocation in dynamic shared memory) in which case other backends won't have that information, so we display extension for such cases. Heavyweight locks, also known as lock manager locks or simply locks, primarily protect SQL-visible objects such as tables. When a server, including a physical replica, 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. pg_stat_reset_subscription_stats ( oid ) void. This can be a host name, an IP address, or a directory path if the connection is via Unix socket. Did this page help you? Waiting to read or truncate multixact information. Waiting for a read from a relation data file. The parameter track_activities enables monitoring of the current command being executed by any server process. Waiting during recovery when WAL data is not available from any source (. Amount of transaction data decoded for streaming in-progress transactions to the decoding output plugin while decoding changes from WAL for this slot. Its purpose is for the same page to be read into the shared buffer. 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. See, Only one row, showing statistics about the WAL receiver from that receiver's connected server. 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. Waiting to read or update the replication progress. Waiting to read or update sub-transaction information. Please refer to your browser's Help pages for instructions. Waiting for background worker to start up. 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. (To prevent ordinary users from hiding their activity from the administrator, only superusers are allowed to change these parameters with SET.). Total number of WAL full page images generated, Number of times WAL data was written to disk because WAL buffers became full. If a backend is in the active state, it may or may not be waiting on some event. Waiting to acquire a lock on a non-relation database object. If the argument is NULL, reset statistics for all subscriptions. It also tracks the total number of rows in each table, and information about vacuum and analyze actions for each table. The LWLock that this article will introduce is a lightweight lock (Lightweight Lock) based on SpinLock. I am not the DBA, but receive reports occasionally when an application is causing load on the system. The buffer_mapping LWLock wait event will be . Waiting for a read during reorder buffer management. This can be used to gauge the delay that, Time elapsed between flushing recent WAL locally and receiving notification that this standby server has written and flushed it (but not yet applied it). Waiting in main loop of logical replication apply process. Heavyweight locks, also known as lock manager locks or simply locks, primarily protect SQL-visible objects such as tables. Waiting in WAL receiver to establish connection to remote server. If the argument is NULL, all counters shown in the pg_stat_slru view for all SLRU caches are reset. Waiting to read or update a process' fast-path lock information. Waiting in WAL receiver to receive data from remote server. This facility is independent of the cumulative statistics system. Waiting for I/O on a transaction status SLRU buffer. Waiting in main loop of startup process for WAL to arrive, during streaming recovery. Waiting for any activity when processing replies from WAL receiver in WAL sender process. Returns the OID of the user logged into this backend. Waiting for a read from the control file. Waiting for other Parallel Hash participants to finish hashing the inner relation. However, current-query information collected by track_activities is always up-to-date. Normally, WAL files are archived in order, oldest to newest, but that is not guaranteed, and does not hold under special circumstances like when promoting a standby or after crash recovery. Waiting for parallel workers to finish computing. Normally these parameters are set in postgresql.conf so that they apply to all server processes, but it is possible to turn them on or off in individual sessions using the SET command. fastpath function call: The backend is executing a fast-path function. your workload peak time if you see LWLock:BufferIO coinciding with pg_stat_reset_single_table_counters ( oid ) void. Re: Improve WALRead() to suck data directly from WAL buffers when possible - Mailing list pgsql-hackers Extension: The server process is waiting for activity in an extension module. wait_event will identify the specific wait point. A backend process wants to read a page into shared memory. operations, Large or bloated indexes that require the engine to read more pages than necessary into the shared buffer pool, Lack of indexes that forces the DB engine to read more pages from the tables than necessary, Checkpoints occurring too frequently or needing to flush too many modified pages, Sudden spikes for database connections trying to perform operations on the same page. Waiting to access the multixact offset SLRU cache. 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. Waiting for I/O on a serializable transaction conflict SLRU buffer. Serial number of the client certificate, or NULL if no client certificate was supplied or if SSL is not in use on this connection. DN of the issuer of the client certificate, or NULL if no client certificate was supplied or if SSL is not in use on this connection. The parameter track_wal_io_timing enables monitoring of WAL write times. Waiting to synchronize workers during Parallel Hash Join plan execution. buffer_io: Waiting for I/O on a data page. Waiting for a replication slot to become inactive so it can be dropped. Waiting for activity from a child process while executing a. Waiting to read or update transaction status. 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 live rows fetched by sequential scans and index entries returned by index scans in this database, Number of live rows fetched by index scans 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. (The path case can be distinguished because it will always be an absolute path, beginning with /.). 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. These access functions use a backend ID number, which ranges from one to the number of currently active backends. This effect can mean that you have a small shared buffers setting. BufferCacheHitRatio and LWLock:BufferIO wait 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. This has no effect in a quorum-based synchronous replication. My application is using Postgres as DBMS, the version of Postgres that i'm using is 10.3 with the extension Postgis installed. Waiting to access a parallel query's information about type modifiers that identify anonymous record types. Waiting to read or update shared multixact state. The server process is idle. Pointers to free buffers and to the next victim are protected by one buffer strategy lock spinlock. Waiting to read or update the current state of autovacuum workers. Returns the time when this process was started. 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 for a write during a file copy operation. Waiting for other Parallel Hash participants to finish repartitioning. The combination of certificate serial number and certificate issuer uniquely identifies a certificate (unless the issuer erroneously reuses serial numbers). Indexes can be used by simple index scans, bitmap index scans, and the optimizer. See, OID of the database this backend is connected to, Name of the database this backend is connected to, Name of the user logged into this backend, Name of the application that is connected to this backend. The next use of statistical information will cause a new snapshot to be fetched. Presently, the collector can count accesses to tables and indexes in both disk-block and individual-row terms. (See Chapter20 for details about setting configuration parameters.). The server process is waiting for a timeout to expire. This should not be used for data integrity checks. Waiting for a relation data file to be truncated. Waiting to allocate or free a replication slot. Waiting for a write of a timeline history file received via streaming replication. pg_stat_get_snapshot_timestamp () timestamp with time zone, Returns the timestamp of the current statistics snapshot, or NULL if no statistics snapshot has been taken. Waiting for truncate of mapping data during a logical rewrite. Waiting for other Parallel Hash participants to finish loading a hash table. But if you want to see new results with each query, be sure to do the queries outside any transaction block. Text of this backend's most recent query. BK_1935: "IObuffer_locks,ControlLock()"IOControlLockControlLockIOSlruSharedData. See, One row only, showing statistics about the WAL archiver process's activity. Waiting for an elected Parallel Hash participant to finish allocating more buckets. For more information on lightweight locks, see Locking Overview. Table28.19. finish their input/output (I/O) operations when concurrently trying to access a page. The pg_stat_bgwriter view will always have a single row, containing global data for the cluster. Time when this process was started. ; Ensure that filesystem journaling is turned off for data files and WAL files. 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. There is no order to the granting of LWLocks and in a high concurrency system this can cause contention. Waiting in main loop of checkpointer process. For tranches registered by extensions, the name is specified by extension and this will be displayed as wait_event. Waiting in main loop of WAL writer process. 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 function pg_stat_get_backend_idset provides a convenient way to generate one row for each active backend for invoking these functions. Additional Statistics Functions. Waiting for a buffered file to be truncated. All temporary files are counted, regardless of why the temporary file was created (e.g., sorting or hashing), and regardless of the, Total amount of data written to temporary files by queries in this database. workload into more reader nodes. The server process is waiting for an I/O operation to complete. Waiting for I/O on a multixact offset buffer. pg_stat_get_backend_pid ( integer ) integer, pg_stat_get_backend_start ( integer ) timestamp with time zone. You can split your PostgreSQL utilizes lightweight locks (LWLocks) to synchronize and control access to the buffer content. A database-wide ANALYZE is recommended after the statistics have been reset. 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. Waiting to add a message in shared invalidation queue. For example, to show the PIDs and current queries of all backends: Table28.20. See, One row for each table in the current database, showing statistics about I/O on that specific table. Resets statistics for a single subscription shown in the pg_stat_subscription_stats view to zero. Waiting for mapping data to reach durable storage during a logical rewrite. Resets statistics to zero for a single SLRU cache, or for all SLRUs in the cluster. Waiting for a write while adding a line to the data directory lock file. Possible values are: catchup: This WAL sender's connected standby is catching up with the primary. Number of times in-progress transactions were streamed to the decoding output plugin while decoding changes from WAL for this slot. The full object locks which last (usually) for the duration of a transaction and which you can see in pg_locks have info about them stored in shared memory. Waiting to manage an extension's space allocation in shared memory. Waiting for a logical replication remote server to change state. Using pg_stat_reset() also resets counters that autovacuum uses to determine when to trigger a vacuum or an analyze. This category is useful for modules to track custom waiting points. 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. Waiting to read or update replication slot state. Waiting for any activity when processing replies from WAL receiver in WAL sender process. This facility is independent of the collector process. Waiting for WAL buffers to be written to disk. might need to increase it or scale up your DB instance class. idle in transaction (aborted): This state is similar to idle in transaction, except one of the statements in the transaction caused an error. Buffer pin waits can be protracted if another process holds an open cursor which last read data from the buffer in question. By default the query text is truncated at 1024 bytes; this value can be changed via the parameter track_activity_query_size. The latter will be less if any dead or not-yet-committed rows are fetched using the index, or if any heap fetches are avoided by means of an index-only scan. The pg_stat_replication view will contain one row per WAL sender process, showing statistics about replication to that sender's connected standby server. If state is active this field shows the identifier of the currently executing query. See, One row for each index in the current database, showing statistics about accesses to that specific index. idle in transaction: The backend is in a transaction, but is not currently executing a query. Waiting to replace a page in WAL buffers. Waiting for logical rewrite mappings to reach durable storage. Waiting to ensure that a table selected for autovacuum still needs vacuuming. Number of in-progress transactions streamed to the decoding output plugin after the memory used by logical decoding to decode changes from WAL for this slot has exceeded logical_decoding_work_mem. Waiting to read or update shared notification state. Waiting for a newly created timeline history file to reach durable storage. It can be joined to pg_stat_activity or pg_stat_replication on the pid column to get more details about the connection. wait_event will identify the specific wait point. [prev in list] [next in list] [prev in thread] [next in thread] List: postgresql-general Subject: Re: [HACKERS] [PATCH] Refactoring of LWLock tranches From: Ildus Kurbangaliev <i.kurbangaliev postgrespro !