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 changes to a relation data file to reach durable storage. Waiting for a relation data file to be truncated. Resets some cluster-wide statistics counters to zero, depending on the argument. streaming: This WAL sender is streaming changes after its connected standby server has caught up with the primary. For an asynchronous standby, the replay_lag column approximates the delay before recent transactions became visible to queries. backup: This WAL sender is sending a backup. See, One row for each table in the current database, showing statistics about I/O on that specific table. 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. 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. Waiting to access the transaction status SLRU cache. Waiting for a write when creating a new WAL segment by copying an existing one. fastpath function call: The backend is executing a fast-path function. It can be joined to pg_stat_activity or pg_stat_replication on the pid column to get more details about the connection. Waiting for a read while adding a line to the data directory lock file. buffer_mapping | DBmarlin Docs and Knowledge Base Returns the IP address of the client connected to this backend. Waiting in main loop of logical replication apply process. pg_stat_get_backend_client_addr ( integer ) inet. Avoid PostgreSQL LWLock:buffer_content locks in Amazon Aurora: Tips and 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. PostgreSQL Source Code: src/include/storage/lwlock.h Source File Such a system would show similar times while new WAL is being generated, but would differ when the sender becomes idle. Resets statistics for a single subscription shown in the pg_stat_subscription_stats view to zero. The pg_stat_bgwriter view will always have a single row, containing global data for the cluster. Waiting for truncate of mapping data during a logical rewrite. Amount of decoded transaction data spilled to disk while performing decoding of changes from WAL for this slot. Waiting in main loop of logical apply process. Waiting to select the starting location of a synchronized table scan. The per-index statistics are particularly useful to determine which indexes are being used and how effective they are. 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. 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 the control file to reach durable storage. 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, last_msg_send_time timestamp with time zone, Send time of last message received from origin WAL sender, last_msg_receipt_time timestamp with time zone, 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, Host of the PostgreSQL instance this WAL receiver is connected to. The parameter track_io_timing enables monitoring of block read and write times. This includes the sync time when wal_sync_method is either open_datasync or open_sync. Returns the time when the backend's current transaction was started. When using the statistics to monitor collected data, it is important to realize that the information does not update instantaneously. Waiting to send bytes to a shared message queue. Possible values are: async: This standby server is asynchronous. Possible values are: active: The backend is executing a query. 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. (For example, in psql you could issue \d+ pg_stat_activity.) Autovacuum worker or launcher waiting to update or read the current state of autovacuum workers. Top-level transaction identifier of this backend, if any. Waiting for data to reach durable storage while adding a line to the data directory lock file. Waiting to read or update shared notification state. When analyzing statistics interactively, or with expensive queries, the time delta between accesses to individual statistics can lead to significant skew in the cached statistics. Occasionally i noticed that in random interval of times the dbms become slow and get stuck on a few SELECT queries. 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 recovery conflict resolution for a vacuum cleanup. See, One row per WAL sender process, showing statistics about replication to that sender's connected standby server. Waiting for a write to the relation map file. 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. The functions for per-function statistics take a function OID. Waiting to access the list of finished serializable transactions. Note, however, that the existence of a session and its general properties such as its sessions user and database are visible to all users. catchup: This WAL sender's connected standby is catching up with the primary. It can also count calls to user-defined functions and the total time spent in each one. IP address of the client connected to this WAL sender. Waiting to access the commit timestamp SLRU cache. When using the cumulative statistics views and functions to monitor collected data, it is important to realize that the information does not update instantaneously. Amount of transaction data decoded for sending transactions to the decoding output plugin while decoding changes from WAL for this slot. Waiting for an asynchronous prefetch from a relation data file. 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. The pg_stat_replication view will contain one row per WAL sender process, showing statistics about replication to that sender's connected standby server. Resets statistics for a single table or index in the current database or shared across all databases in the cluster to zero. 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. The most possible reason for why you see LWLockTranche/buffer_mapping this form See, One row per connection (regular and replication), showing information about SSL used on this connection. Waiting for a write of mapping data during a logical rewrite. Every PostgreSQL process collects statistics locally, then updates the shared data at appropriate intervals. 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). Presently, the collector can count accesses to tables and indexes in both disk-block and individual-row terms. There have been several occasions when a query is being executed dozens of times simultaneously by one or many users. Waiting for parallel query dynamic shared memory allocation. Waiting for I/O on a sub-transaction SLRU buffer. For an asynchronous standby, the replay_lag column approximates the delay before recent transactions became visible to queries. Alternatively, one can build custom views using the underlying cumulative statistics functions, as discussed in Section28.2.24. The type of event for which the backend is waiting, if any; otherwise NULL. Waiting for data to reach durable storage while creating the data directory lock file. Waiting in main loop of autovacuum launcher process. Waiting for a new WAL segment created by copying an existing one to reach durable storage. Most such locks protect a particular data structure in shared memory. 105 #define BUFFER_MAPPING_LWLOCK_OFFSET NUM_INDIVIDUAL_LWLOCKS. Waiting to read or write relation cache initialization file. Waiting to add or examine locks for backends, or waiting to join or exit a locking group (used by parallel query). 202302_Serendipity_Shy_CSDN Waiting for an immediate synchronization of a relation data file to durable storage. Wait Events of Type Extension. Write-Ahead Logging (WAL) is a standard method for ensuring data integrity. Lag times work automatically for physical replication. This can be a host name, an IP address, or a directory path if the connection is via Unix socket. 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. Per-Backend Statistics Functions, pg_stat_get_backend_idset () setof integer. For details such as the functions' names, consult the definitions of the standard views. Waiting for a write while adding a line to the data directory lock file. Waiting to create, drop or use a replication origin. Waiting for I/O on a multixact_member buffer. Waiting for a write of a timeline history file received via streaming replication. Waiting for the relation map file to reach durable storage. Waiting to read or update the progress of one replication origin. Waiting for a barrier event to be processed by all backends. These numbers do not act as stated above; instead they update continuously throughout the transaction. If the argument is NULL, all counters shown in the pg_stat_slru view for all SLRU caches are reset. Waiting for WAL to be flushed in WAL sender process. Waiting for data to reach durable storage while creating the data directory lock file. 106 . idle in transaction: The backend is in a transaction, but is not currently executing a query. The IO:DataFileRead wait event occurs while data is The functions for per-function statistics take a function OID. This counter is incremented each time a transaction is streamed, and the same transaction may be streamed multiple times. Waiting for a write to a replication slot control file. 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. Waiting to read or record conflicting serializable transactions. 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. Waiting for I/O on a serializable transaction conflict SLRU buffer. Sometimes it may be more convenient to obtain just a subset of this information. wait_event will identify the type of lock awaited. Note that only tables, indexes, and functions in the current database can be seen with these functions. A backend process wants to read a page into shared memory. Aurora PostgreSQL wait events - Amazon Aurora
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