How Redis AOF Rewrite Shrinks Log Files and Keeps Data Consistent

Redis’s Append‑Only File (AOF) persistence records every write command, so the AOF file continuously grows. If unchecked, a large AOF file can degrade Redis performance and increase recovery time.

Example commands:

RPUSH list "A" "B"
RPUSH list "C"
RPUSH list "D" "E"
LPOP list
LPOP list

Some of these commands become redundant because they do not affect the final database state.

To combat AOF bloat, Redis provides an AOF rewrite (or rewrite ) feature that creates a new, compact AOF file containing only the minimal set of commands needed to reconstruct the current dataset.

For the list example, the five original commands can be replaced by a single command: RPUSH list "C" "D" "E" The rewrite works by reading the current value of each key from the database and writing a single command that reproduces that value.

Because rewriting involves heavy I/O, Redis performs it in a child process, allowing the parent process to continue serving client requests.

During the rewrite, new write commands are stored in an AOF rewrite buffer . When the child finishes, it signals the parent, which then:

Appends the buffered commands to the new AOF file, ensuring the file reflects the latest state.

Atomically renames the new file over the old one, completing the replacement.

Only the brief signal‑handling phase blocks the server, minimizing impact on availability.