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Paiboon Panusbordee
Asked: 2014-01-24 06:57:42 +0800 CST

Can Redis RDB corrupt?

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In redis.io site, it states that RDB is less durable than AOF. Does this mean there is some possibility of database corruption, and complete data loss if power is lost during a save operation?

redis

2 Answers

  1. The .rdb itself "cannot" be corrupt as the dump is first saved to a tmp file and renamed to the dump after. Ofcourse there can go something wrong when renaming. So there is a very very small chance, but it is not likely.

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  2. Best Answer

    It is possible for the RDB file to become corrupt if the underlying datastore has problems. Redis includes a utility redis-check-dump to validate a file, and you could use this to check the newly written dump file for consistency.

    If an RDB is corrupt on startup, Redis will fail to start and report a somewhat cryptic error. There is a pull request:

    https://github.com/antirez/redis/pull/1744

    To make the check program run automatically, but it has not been merged (yet).

    The dump file is written in a background thread, which means that it cannot contain a 100% up to date copy of the key space. To get this, you need to use the AOF file and set it to sync after every write (which has performance implications).

    Redis' architecture allows you to build many different solutions to this. You could turn on AOF writing on the master with "never" fsync, then create two slave servers, one of which only created RDB files every 10 minutes and another that used AOF with "always" or "everysec" fsync. This would give you built-in redundancy on the master so long as the disk never failed, but if it did you could take the AOF file from the slave and use it to bring the master back. If that failed, you could go to the RDB slave, but in this case you might lose the data written since the last 10 minute dump.

    This flexibility is part of what makes Redis so powerful: you can choose, based on the data you are storing what level of redundancy to use.

    Alternatively, you can go with a hosted Redis service and let them worry about the details.

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