These numbers do not act as stated above; instead they update continuously throughout the transaction. Waiting to access the list of predicate locks held by serializable transactions. Waiting for any activity when processing replies from WAL receiver in WAL sender process. In addition, background workers registered by extensions may have additional types. Waiting to read or update multixact offset mappings. 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. LWLock:BufferIO. 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. Waiting to receive bytes from a shared message queue. Waiting for a read of a serialized historical catalog snapshot. Waiting for an elected Parallel Hash participant to allocate the initial hash table. If this field is null, it indicates that the client is connected via a Unix socket on the server machine. Waiting to read or update dynamic shared memory state. Waiting for confirmation from a remote server during synchronous replication. Current overall state of this backend. 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. Table28.15.pg_stat_replication_slots View, A unique, cluster-wide identifier for the replication slot. Amount of transaction data decoded for sending transactions to the decoding output plugin while decoding changes from WAL for this slot. It works like this: postgres/README at master postgres/postgres GitHub 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 the progress of one replication origin. idle in transaction (aborted): This state is similar to idle in transaction, except one of the statements in the transaction caused an error. Cumulative statistics are collected in shared memory. Synchronous state of this standby server. Waiting for data to reach durable storage while creating the data directory lock file. The server process is waiting for exclusive access to a data buffer. LWLock:BufferIO - Amazon Relational Database Service AWSDocumentationAmazon RDS and Aurora DocumentationUser Guide Relevant engine versionsContextCausesActions LWLock:BufferIO Note that this includes the transactions that are streamed and/or spilled. 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. Waiting for any activity when processing replies from WAL receiver in WAL sender process. The functions for per-function statistics take a function OID. Waiting for WAL to reach durable storage during bootstrapping. Waiting for the version file to be written while creating a database. The LWLock:BufferIO event occurs when Aurora PostgreSQL or RDS for PostgreSQL is waiting for other processes to 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. See, Only one row, showing statistics about the WAL receiver from that receiver's connected server. Waiting to read or write relation cache initialization file. Waiting to update limits on transaction id and multixact consumption. > However, someone with deeper knowledge of page pinning and buffer manager > internals could certainly devise a better solution. Waiting for the termination of another backend. Resetting these counters can cause autovacuum to not perform necessary work, which can cause problems such as table bloat or out-dated table statistics. 5mins of Postgres E25: Postgres lock monitoring, LWLocks and the log Waiting for a read of a logical mapping during reorder buffer management. [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 ! See, One row for each table in the current database, showing statistics about accesses to that specific table. Waiting to access a parallel query's information about composite types. Waiting for a read from a relation data file. 214 . The pg_statio_ views are primarily useful to determine the effectiveness of the buffer cache. Waiting for parallel query dynamic shared memory allocation. Resets all statistics counters for the current database to zero. Waiting for a write during a file copy operation. lock_manager See, One row per connection (regular and replication), showing information about GSSAPI authentication and encryption used on this connection. See, At least one row per subscription, showing information about the subscription workers. Number of times WAL files were synced to disk via issue_xlog_fsync request (if fsync is on and wal_sync_method is either fdatasync, fsync or fsync_writethrough, otherwise zero). The access functions for per-database statistics take a database OID as an argument to identify which database to report on. Time when the currently active query was started, or if state is not active, when the last query was started. Waiting for a write of a WAL page during bootstrapping. Tuning Input/Output (I/O) Operations for PostgreSQL Waiting for a write of a newly created timeline history file. Waiting for a write while initializing a new WAL file. quorum: This standby server is considered as a candidate for quorum standbys. streaming: This WAL sender is streaming changes after its connected standby server has caught up with the primary. Since collection of statistics adds some overhead to query execution, the system can be configured to collect or not collect information. wait_event will contain a name identifying the purpose of the lightweight lock. Waiting in main loop of WAL sender process. Waiting for a write of a WAL page during bootstrapping. Waiting for a write to update the control file. It can be joined to pg_stat_activity or pg_stat_replication on the pid column to get more details about the connection. gorthx on Twitter Waiting to write a protocol message to a shared message queue. pg_stat_get_backend_client_port ( integer ) integer. See, One row for each table in the current database, showing statistics about I/O on that specific table. Using pg_stat_reset() also resets counters that autovacuum uses to determine when to trigger a vacuum or an analyze. Waiting for I/O on a commit timestamp SLRU buffer. 'Re: [HACKERS] [PATCH] Refactoring of LWLock tranches' - MARC 202302_Serendipity_Shy_CSDN But access to that shared memory requires the protection of light-weight locks, which should last for only nanoseconds or microseconds while the memory access is actually occuring. Top-level transaction identifier of this backend, if any. pg_stat_get_backend_client_addr ( integer ) inet. Number of data page checksum failures detected in this database (or on a shared object), or NULL if data checksums are not enabled. Waiting for the group leader to clear the transaction ID at end of a parallel operation. Waiting to acquire an advisory user lock. The pg_stat_user_indexes and pg_stat_sys_indexes views contain the same information, but filtered to only show user and system indexes respectively. See, Time when the current transaction was started. 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. This is used by system processes waiting for activity in their main processing loop. might need to increase it or scale up your DB instance class. For example, to show the PIDs and current queries of all backends: Table28.20. Simple test for lock_waits log messages. Waiting to read or update shared notification state. Waiting to read or update vacuum-related information for a B-tree index. Additional functions related to statistics collection are listed in Table28.19. Waiting to send bytes to a shared message queue. wait_event will identify the specific wait point. Waiting for a write to a relation data file. This field is truncated if the principal is longer than NAMEDATALEN (64 characters in a standard build). A transaction can also see its own statistics (not yet flushed out to the shared memory statistics) in the views pg_stat_xact_all_tables, pg_stat_xact_sys_tables, pg_stat_xact_user_tables, and pg_stat_xact_user_functions. Possible types are. Waiting in main loop of checkpointer process. Waiting to elect a Parallel Hash participant to allocate a hash table. Logical decoding plugins may optionally emit tracking messages; if they do not, the tracking mechanism will simply display NULL lag. Waiting for the page number needed to continue a parallel B-tree scan to become available. 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. The counter gets incremented for both top-level transactions and subtransactions. Waiting for background worker to start up. A backend process wants to read a page into shared memory. Last write-ahead log location already received and written to disk, but not flushed. Waiting to synchronize workers during Parallel Hash Join plan execution. Connection string used by this WAL receiver, with security-sensitive fields obfuscated. Waiting for other process to be attached in shared message queue. Each such lock protects a particular data structure in shared memory. Javascript is disabled or is unavailable in your browser. buffer_io: Waiting for I/O on a data page. The lag times reported in the pg_stat_replication view are measurements of the time taken for recent WAL to be written, flushed and replayed and for the sender to know about it. Time at which the last data page checksum failure was detected in this database (or on a shared object), or NULL if data checksums are not enabled. The parameter track_activities enables monitoring of the current command being executed by any server process. Time at which these statistics were last reset. 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. Returns the time when the backend's current transaction was started. If state is active this field shows the currently executing query. Waiting for a read during reorder buffer management. Number of times WAL buffers were written out to disk via XLogWrite request. See, One row per database, showing database-wide statistics. If a backend is in the active state, it may or may not be waiting on some event. Waiting to access a shared tuple store during parallel query. Identifier of this backend's most recent query. Waiting in main loop of background writer process background worker. 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. If the standby server has entirely caught up with the sending server and there is no more WAL activity, the most recently measured lag times will continue to be displayed for a short time and then show NULL. The server process is waiting for activity on a socket connected to a user application. In all other states, it shows the identifier of last query that was executed. See Section30.5 for more information about the internal WAL function XLogWrite. pg_stat_get_backend_wait_event ( integer ) text. Waiting between writes while performing a checkpoint. (For example, in psql you could issue \d+ pg_stat_activity.) Waiting to apply WAL during recovery because of a delay setting. Waiting for truncate of mapping data during a logical rewrite. Waiting for other Parallel Hash participants to finish loading a hash table. 39919 LWLock buffer_mapping 5119 Client ClientRead 3116 IO DataFileRead . Waiting for a replication origin to become inactive to be dropped. See. The pg_stat_recovery_prefetch view will contain only one row. Waiting for a relation data file to be extended. 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 for each backend (including autovacuum worker processes) running, One row only, showing statistics about the WAL archiver process's activity. replication_slot_io: Waiting for I/O on a replication slot. Waiting for a timeline history file received via streaming replication to reach durable storage. 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. This view will only contain information on standby servers, since conflicts do not occur on master servers. 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. Re: Improve WALRead() to suck data directly from WAL buffers when Additional functions related to the cumulative statistics system are listed in Table28.34. Number of backends currently connected to this database. Waiting for logical rewrite mappings to reach durable storage during a checkpoint. Waiting to receive bytes from a shared message queue. Waiting for a logical replication remote server to change state. Resets statistics for a single table or index in the current database or shared across all databases in the cluster to zero. Waiting for a write of a newly created timeline history file. 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. (See Chapter19 for details about setting configuration parameters.). LWTRANCHE_BUFFER_CONTENT @ LWTRANCHE_BUFFER_CONTENT. Host name of the connected client, as reported by a reverse DNS lookup of client_addr. Use partitioned tables (which also have partitioned indexes). Waiting to read or update the fast-path lock information. For more information, see LWLock:buffer_content (BufferContent). This can be used to gauge the delay that. The LWLock:BufferIO wait event precedes the IO:DataFileRead wait event. Such a system would show similar times while new WAL is being generated, but would differ when the sender becomes idle. Returns the wait event type name if this backend is currently waiting, otherwise NULL. 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. Doing this helps Waiting for SLRU data to reach durable storage during a checkpoint or database shutdown. BufferCacheHitRatio and LWLock:BufferIO wait Waiting for data to reach durable storage while assigning a new WAL sync method. Waiting to allocate or free a replication slot. This block has to be read from outside the shared buffer pool, defined by the 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. If you've got a moment, please tell us how we can make the documentation better. Waiting to access the commit timestamp SLRU cache. (See Chapter20 for details about setting configuration parameters.). Waiting for a replication slot to become inactive to be dropped. Waiting in main loop of the statistics collector process. quorum: This standby server is considered as a candidate for quorum standbys. 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 parameter track_io_timing enables monitoring of block read and write times. This field is truncated like client_dn. The lag times reported in the pg_stat_replication view are measurements of the time taken for recent WAL to be written, flushed and replayed and for the sender to know about it. streaming: This WAL sender is streaming changes after its connected standby server has caught up with the primary. Possible values are: Top-level transaction identifier of this backend, if any. The pg_stat_database view will contain one row for each database in the cluster, plus one for shared objects, showing database-wide statistics. IP address of the client connected to this WAL sender. 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. pg_blocking_pids function. See, One row for each table in the current database, showing statistics about accesses to that specific table. Every PostgreSQL process collects statistics locally, then updates the shared data at appropriate intervals. Waiting to get a snapshot or clearing a transaction id at transaction end. Total amount of data written to temporary files by queries in this database. Statistics Functions. Waiting to read or update the last value set for a transaction commit timestamp. Copyright 1996-2023 The PostgreSQL Global Development Group, PostgreSQL 15.2, 14.7, 13.10, 12.14, and 11.19 Released, 28.2.1. workload into more reader nodes. The next use of statistical information will (when in snapshot mode) cause a new snapshot to be built or (when in cache mode) accessed statistics to be cached. 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 WAL to be flushed in WAL sender process. The function pg_stat_get_backend_idset provides a convenient way to generate one row for each active backend for invoking these functions. Connection string used by this WAL receiver, with security-sensitive fields obfuscated. 213 * Prior to PostgreSQL 9.4, we used an enum type called LWLockId to refer. Waiting to access the list of finished serializable transactions. There is no order to the granting of LWLocks and in a high concurrency system this can cause contention. Re: Improve WALRead() to suck data directly from WAL buffers when possible - Mailing list pgsql-hackers Returns the text of this backend's most recent query. 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. See, One row for each sequence in the current database, showing statistics about I/O on that specific sequence. Statistics Collection Configuration, One row per server process, showing information related to the current activity of that process, such as state and current query. Waiting for I/O on a multixact_member buffer. This facility is independent of the cumulative statistics system. Process ID of the parallel group leader, if this process is a parallel query worker. The pg_stat_subscription_stats view will contain one row per subscription. Waiting to retrieve or store information about serializable transactions. purpose is for the same page to be read into the shared buffer. Waiting to allocate or assign a transaction id. Number of times in-progress transactions were streamed to the decoding output plugin while decoding changes from WAL for this slot. See, One row per connection (regular and replication), showing information about SSL used on this connection. Waiting to read or update transaction status. This can be used to gauge the delay that synchronous_commit level remote_apply incurred while committing if this server was configured as a synchronous standby. Detailed Description . PostgreSQL utilizes lightweight locks (LWLocks) to synchronize and control access to the buffer content.
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