BK_1935: "IObuffer_locks,ControlLock()"IOControlLockControlLockIOSlruSharedData. 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. If this field is null, it indicates that the client is connected via a Unix socket on the server machine. Waiting to fill a dynamic shared memory backing file with zeroes. The server process is waiting for a timeout to expire. Number of times WAL buffers were written out to disk via XLogWrite request. Table28.6. wait_event will identify the specific wait point. The pg_stat_ssl view will contain one row per backend or WAL sender process, showing statistics about SSL usage on this connection. (For example, in psql you could issue \d+ pg_stat_activity.) Current overall state of this backend. Lag times work automatically for physical replication. Waiting for other Parallel Hash participants to finish inserting tuples into new buckets. Waiting for a write of a WAL page during bootstrapping. See, One row per database, showing database-wide statistics about query cancels due to conflict with recovery on standby servers. Waiting to add or examine locks for backends, or waiting to join or exit a locking group (used by parallel query). Waiting in main loop of checkpointer process. Time elapsed between flushing recent WAL locally and receiving notification that this standby server has written, flushed and applied it. The parameter track_functions enables tracking of usage of user-defined functions. 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. Waiting to synchronize workers during Parallel Hash Join plan execution. Waiting for a read of a serialized historical catalog snapshot. See, Time when the current transaction was started. Waiting for a replication slot to become inactive so it can be dropped. Common causes for the LWLock:BufferIO event to appear in top waits include the following: Multiple backends or connections trying to access the same page that's The last article introduced SpinLock in PostgreSQL. Waiting to access the list of predicate locks held by serializable transactions. lock_manager Waiting for a relation data file to be extended. Waiting during recovery when WAL data is not available from any source (. please use By default the query text is truncated at 1024 bytes; this value can be changed via the parameter track_activity_query_size. Waiting for logical replication remote server to change state. Such a system would show similar times while new WAL is being generated, but would differ when the sender becomes idle. Possible values are: catchup: This WAL sender's connected standby is catching up with the primary. Pointers to free buffers and to the next victim are protected by one buffer strategy lock spinlock. @ LWTRANCHE_REPLICATION_SLOT_IO. wait_event will identify the specific wait point. See, One row per WAL sender process, showing statistics about replication to that sender's connected standby server. Waiting to access the list of finished serializable transactions. Text of this backend's most recent query. David Christensen on Twitter. Waiting for SLRU data to reach durable storage during a checkpoint or database shutdown. Serial number of the client certificate, or NULL if no client certificate was supplied or if SSL is not in use on this connection. Waiting to read or update the fast-path lock information. Waiting in main loop of WAL sender process. Thanks for letting us know this page needs work. Waiting to insert WAL into a memory buffer. Additional functions related to the cumulative statistics system are listed in Table28.34. LWLock:BufferIO - Amazon Relational Database Service AWSDocumentationAmazon RDS and Aurora DocumentationUser Guide Relevant engine versionsContextCausesActions LWLock:BufferIO Waiting to write a protocol message to a shared message queue. Waiting for a write during reorder buffer management. Waiting for a read of a two phase state file. The server process is waiting for an I/O operation to complete. Its Waiting for a relation data file to be extended. Returns the process ID of the server process attached to the current session. 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. Waiting to access the multixact offset SLRU cache. Waiting for logical replication remote server to send data for initial table synchronization. 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. Synchronous state of this standby server. Waiting for background worker to start up. This is controlled by configuration parameters that are normally set in postgresql.conf. Topics Relevant engine versions Context Causes Actions Relevant engine versions The overhead of a file is much more than wasting the remainder of a page. 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. Time at which these statistics were last reset. , LWTRANCHE_MXACTMEMBER_BUFFERS, LWTRANCHE_ASYNC_BUFFERS, LWTRANCHE_OLDSERXID_BUFFERS, LWTRANCHE_WAL_INSERT, LWTRANCHE_BUFFER_CONTENT, LWTRANCHE_BUFFER_IO_IN_PROGRESS, LWTRANCHE . postgres7 Slru--1. This facility is independent of the collector process. 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). Tune max_wal_size and checkpoint_timeout based on 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. Waiting for a read from a replication slot control file. Waiting to read or update the last value set for the transaction timestamp. Additional Statistics Functions. - 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 TCP port number that the client is using for communication with this WAL sender, or -1 if a Unix socket is used, Time when this process was started, i.e., when the client connected to this WAL sender. See, One row for each table in the current database, showing statistics about I/O on that specific table. Time elapsed between flushing recent WAL locally and receiving notification that this standby server has written and flushed it (but not yet applied it). The argument can be one of CommitTs, MultiXactMember, MultiXactOffset, Notify, Serial, Subtrans, or Xact to reset the counters for only that entry. Waiting in main loop of checkpointer process. Waiting to manage an extension's space allocation in shared memory. In contrast, when starting from an unclean shutdown (e.g., after an immediate shutdown, a server crash, starting from a base backup, and point-in-time recovery), all statistics counters are reset. PostgreSQL utilizes lightweight locks (LWLocks) to synchronize and control access to the buffer content. 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. See, Only one row, showing statistics about the WAL receiver from that receiver's connected server. Waiting for activity from child process when executing. 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 a barrier event to be processed by all backends. Waiting to read or truncate multixact information. ; Ensure that filesystem journaling is turned off for data files and WAL files. For client backends, this is the time the client connected to the server. 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 to read or update notification messages. Waiting for data to reach durable storage while adding a line to the data directory lock file. wait_event will identify the specific wait point. replication_slot_io: Waiting for I/O on a replication slot. The pg_stat_user_tables and pg_stat_sys_tables views contain the same information, but filtered to only show user and system tables respectively. Waiting to elect a Parallel Hash participant to allocate more batches. 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. 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. Current overall state of this backend. The pg_statio_ views are primarily useful to determine the effectiveness of the buffer cache. Number of times in-progress transactions were streamed to the decoding output plugin while decoding changes from WAL for this slot. TCP port number that the client is using for communication with this backend, or -1 if a Unix socket is used. 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. Total amount of time spent writing WAL buffers to disk via XLogWrite request, in milliseconds (if track_wal_io_timing is enabled, otherwise zero). The server process is waiting for exclusive access to a data buffer. This can be used to gauge the delay that synchronous_commit level remote_write incurred while committing if this server was configured as a synchronous standby. There is no order to the granting of LWLocks and in a high concurrency system this can cause contention. In all other states, it shows the last query that was executed. Waiting for WAL buffers to be written to disk. Note that only tables, indexes, and functions in the current database can be seen with these functions. Alternatively, one can build custom views using the underlying statistics functions, as discussed in Section28.2.3. Waiting for confirmation from a remote server during synchronous replication. This is controlled by configuration parameters that are normally set in postgresql.conf. The per-table and per-index functions take a table or index OID. 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. quorum: This standby server is considered as a candidate for quorum standbys.