# Create a database and a table

createdb example_db

psql example_db

CREATE TABLE example_table (id INT, name VARCHAR(50));

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# Insert some data into the table

INSERT INTO example_table VALUES (1, 'John'), (2, 'Jane'), (3, 'Bob');

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# Create a backup of the database using the pg_dump utility

pg_dump example_db > backup.sql

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# Modify the table by deleting a row

DELETE FROM example_table WHERE id=3;

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# Create a write-ahead log (WAL) file to record the changes

SELECT pg_switch_xlog();

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# Modify the table again by inserting a new row

INSERT INTO example_table VALUES (4, 'Alice');

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# Create another WAL file

SELECT pg_switch_xlog();

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# Simulate a crash by stopping the PostgreSQL server

sudo systemctl stop postgresql.service

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# Restore the backup

psql example_db < backup.sql

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# Apply the WAL files to roll the database forward to the current state

pg_waldump < pg_wal/000000010000000000000001 | psql example_db

pg_waldump < pg_wal/000000010000000000000002 | psql example_db

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# Verify that the database is now in the correct state

psql example_db

SELECT * FROM example_table;