What is a WAL file?

Question

The write-ahead log or "wal" file is a roll-forward journal that records transactions that have been committed but not yet applied to the main database. Details on the format of the wal file are describe in the WAL format subsection of the main file format document.

How do I view a WAL file?

PostgreSQL does not have a built-in function or view that directly returns WAL file related information. You can however, use this query: SELECT COUNT(*) FROM pg_ls_dir('pg_xlog') WHERE pg_ls_dir ~ '^[0-9A-F]{24}'; that does the job of getting the count of WAL files.

What is a WAL record?

In computer science, write-ahead logging (WAL) is a family of techniques for providing atomicity and durability (two of the ACID properties) in database systems. The changes are first recorded in the log, which must be written to stable storage, before the changes are written to the database.

Where are WAL files?

WAL logs are stored in the directory pg_wal under the data directory, as a set of segment files, normally each 16 MB in size (but the size can be changed by altering the --wal-segsize initdb option).

What are WAL files Postgres?

WAL is short for Write Ahead Log. WALs are used in nearly all modern RDBMS systems to provide durable and atomic transactions. Simply put, any transaction performed on the database is first written out as a WAL file, then applied to the actual on-disk table data files. WAL files are strictly sequential.

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