Sample Exam Questions

From the objective of OSS-DB Exam Silver
S2.4 Backup and restore (Transaction log (WAL) and WAL archive)

Sample Question


Choose two appropriate descriptions for transaction log (WAL) and WAL archiving.

  1. WAL files and WAL archiving are used for Point In Time Recovery (PITR).

  2. The size of each WAL file is 8KB.

  3. The file structures of WAL files and WAL archives are different.

  4. The output destination for the WAL archive is set using the "restore_command" parameter.

  5. By default, WAL files are stored in the "$PGDATA/pg_wal" directory.

※This sample exam is different from those that appear in the actual OSS-DB Exam.

Answer and Explanation

PostgreSQL creates Write Ahead Logging (WAL) to implement an append-only architecture.
If WAL files continue to grow, the disk will become full, so old WAL files are discarded. However, there are times when WAL files should not be discarded because they are used for PITR.
In such cases, configure archiving to periodically save WAL files in a different location.
This is WAL archiving.
WAL files are saved in "$PGDATA/pg_wal" by default, but the destination for the WAL archive copy command should be set in "archive_command."

Therefore, the correct answers are A and E.