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Database
A single database that runs on a database instance.
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Database instance
Database host machine, may contain multiple databases.
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Logical replication
Replication at the level of operations; describes the operation, the arguments and data (e.g., an UPDATE is applied to row X setting column Y = Z).
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Physical replication
Replication of the on-disk data structures after an operation has been applied.
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Primary database (DB)
The customer’s database within a database instance that is being replicated. The source of truth for data for all copies of that database.
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Write-ahead log (WAL)
Log used by a database to log database operations. Used for recovery replay or replication.