THthamer·Aug 5, 2021
It's not only the "VM" experiments but generally the very basic approach to persistence that's kept Redis from being an actual database and has most users (hopefully) only using it as a cache.
Around the same period as this blog post antirez had also announced that he had written a B-Tree that could be potentially used to store Redis data. The code is still up: https://github.com/antirez/otree – needless to say serious storage engines like LevelDB or RocksDB are more than a single 1,000-line C file, while this looked more like a weekend project.
The persistence model that has stayed in Redis is also a pretty basic approach: fork + dump all memory to a single file. Write every command to a file and compact it by doing the same fork + scan/flush. None of this is efficient, and with a tens of GB of cache you get long pauses during fork() as
Read the rest
the page table gets copied to the child process (yes just the table, not the memory pages themselves).
All this to say that his advice on disk I/O is to be taken in the context of his own experience in this domain.