CODEWITHSUNDEEP
redis
Hassan Baig
Hassan Baig

Reputation: 15824

Redis memory usage vs space taken up by back ups

I'm looking at Redis backed up rdb files for a web application. There are 4 such files (for 4 different redis servers working concurrently), sizes being: 13G + 1.6G + 66M + 14M = ~15G

However, these same 4 instances seem to be taking 43.8GB of memory (according to new relic). Why such a large discrepancy between how much space redis data takes up in mem vs disk? Could it be a misconfiguration and can the issue be helped?

Upvotes: 1

Views: 1463

Answers (1)

Spock
Spock

Reputation: 184

I don't think there is any problem.

First of all, the data is stored in compressed format in rdb file so that the size is less than what it is in memory. How small the rdb file is depends on the type of data, but it can be around 20-80% of the memory used by redis

Another reason your memory usage could be more than the actual usage(you can compare the memory from new relic to the one obtained from redis-cli info memory command) is because of memory fragmentation. Whenever redis needs more memory, it will get the memory allocated from the OS, but will not release it easilyly(when the key expires or is deleted). This is not a big issue, as redis will ask for more memory only after using the extra memory that it has. You can also check the memory fragmentation using redis-cli info memory command.

Upvotes: 5

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