Redis save and backup script

This is idea how you can backup the file RDB file.

Basicaly you need to set up two crontab processes. First must perform BGSAVE:

redis-cli bgsave

When this is call, Redis will perform background save. Process usually will finish couple of minutes later. At the end new RDB file will be created.

Second crontab must start 10-15 min later. It needs to move / copy / upload the file to different location. For simplicity here I will simulate a copy to different disk or NFS image.

cp /data/redis/dump.rdb /backup/redis.dump.rdb

Here someone may rise very important question:
What will happen, if Redis begin to save at the time we copy?

Answer is trivial - if you are using modern filesystem, everything is OK and nothing will happen.

This is because of the way Redis do save operation.
First Redis forks, then it saves under temporary file. After process is done, Redis deletes the old file and rename temporary file.

In modern filesystems such EXT2, EXT3, XFS, RaiserFS, NTFS etc., the file always will be copied normally even file is deleted, because delete do not remove the file, but rather remove the only the link to the file. For more information, you may refer to UNIX C unlink() function.

How to do daily backup file

If we just copy the file, today's file will replace yesterday's. This is not always a good idea.

If we want to keep daily backup we can add "date '+%a'" and to append it to the backup filename. The following example also includes configurable directories.

REDIS_SOURCE=/data/redis/dump.rdb
BACKUP_DIR=/backup

BACKUP_PREFIX="redis.dump.rdb"
DAY=`date '+%a'`
REDIS_DEST="$BACKUP_DIR/$BACKUP_PREFIX.$DAY"

cp $REDIS_SOURCE $REDIS_DEST

Crontab set-up

For those who are not familiar with crontab, here you are the crontab script itself:

# Do BGSAVE
0  0 * * *	redis-cli bgsave

# Simple copy
15 0 * * *	cp /data/redis/dump.rdb /backup/redis.dump.rdb

# ... or call more complex script (example is commented)
#15 0 * * *	/scripts/perform_copy.sh

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