What is Multixact in PostgreSQL?

A multixact ID is an internal identifier used support row locking by multiple transactions. Multixact IDs are created when transactions use ” SELECT … FOR UPDATE ” (or one of these lock modes: SHARE, KEY SHARE, NO KEY UPDATE) to lock and update tuples. Multixact IDs live in the pg_multixact directory.

What is WalSenderWaitForWAL?

Client:WalSenderWaitForWAL. A process is waiting for the write-ahead log (WAL) to be flushed in the WAL sender process. Client:WalSenderWriteData. A process is waiting for any activity when processing replies from the write-ahead log (WAL) receiver in the WAL sender process.

What is stats collector?

The stats collector process collects statistics about the database. It’s an optional process with the default value as on. The process keeps track of access to tables and indexes in both disk-block and individual row-terms. It also keeps track of record counts for tables, and tracks the vacuum and analyze actions.

What is Multixact?

Multixact IDs are used to support row locking by multiple transactions. Since there is only limited space in a tuple header to store lock information, that information is encoded as a “multiple transaction ID”, or multixact ID for short, whenever there is more than one transaction concurrently locking a row.

What is Autovacuum in PostgreSQL?

Introduced in PostgreSQL 8.1, the AUTOVACUUM daemon is an optional feature that automatically vacuums the database so that you don’t have to manually run the VACUUM statement. The AUTOVACUUM daemon is made up of multiple processes that reclaim storage by removing obsolete data or tuples from the database.

What is AccessShareLock in PostgreSQL?

The AccessShareLock that is created for read queries like the select statements, and AccessExclusiveLock that is created for operations that modify the whole table. There are several more lock modes in PostgreSQL. ACCESS SHARE — Acquired by queries that only read from a table but do not modify it.

What is Work_mem in PostgreSQL?

work_mem is a configuration within Postgres that determines how much memory can be used during certain operations. At its surface, the work_mem setting seems simple: after all, work_mem just specifies the amount of memory available to be used by internal sort operations and hash tables before writing data to disk.

How replication works in PostgreSQL?

Streaming replication in PostgreSQL works on log shipping. Every transaction in postgres is written to a transaction log called WAL (write-ahead log) to achieve durability. A slave uses these WAL segments to continuously replicate changes from its master.

What is Oracle stat collection?

In Oracle Database, optimizer statistics collection is the gathering of optimizer statistics for database objects, including fixed objects. The database can collect optimizer statistics automatically. You can also collect them manually using the DBMS_STATS package.

What is Pg_stat_all_tables?

The pg_stat_all_tables view shows one row for each table in the current database (including TOAST tables) to display statistics about accesses to that specific table. Access statistics from segment instances are ignored. …