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Comment by rgbimbochamp

6 hours ago

Those help but the main write speed gain is the WAL, that uses preallocated mmap segments to avoid a write(2) per durable mutation while preserving crash recovery. AES hashing mainly helps Bloom filter point lookups and LZ4 mainly helps SSTable I/O. Scans benefit indirectly, but don’t yet use a custom SIMD merge loop.

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rgbimbochamp

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bestouff  5 hours ago

I said elsewhere this doesn't survive a power loss.

  • taneq  5 hours ago

    While it’s important to make this explicit, at what point do we just assume a high-reliability UPS is table stakes?

    Of course, if you need SIL2 type reliability then you need to assume any given hardware component can spontaneously combust and become a total loss, at which point the data loss caused by a power cut is a rounding error.

    • toast0  3 hours ago

      > While it’s important to make this explicit, at what point do we just assume a high-reliability UPS is table stakes?

      Several years after they become commercially available?

      My experience with small UPSes is they tend to cook the batteries and you don't find out until they switch the load and the battery doesn't hold up.

      Large facility UPSes tend to do better, but automatic transfer switches have a tendancy to fail ocassionally. If you're hosted in many locations, it's not unusual to have a couple ATS failures per decade.

      All that said, unexpected power loss is certainly one reason that writes may be lost, but OSes crash too. Disk firmware can also crash, but if thst bricks the disk, writes in progress don't really matter. Sometimes cabling fails. Or you get a uncorrectable ECC error (which will typically cause an OS panic... unless you're running a very fancy OS, but if it's in dirty disk backed page, even a fancy OS wouldn't save you)

      Plenty of applications don't need or want to pay the cost for full commit to disk, but calling something durable when it's not committed to disk is inaccurate.

      And that's before we get into the whole thing where the OS and the disk like to return success when things haven't quite finished.

    • whilenot-dev  3 hours ago

      What's got this to do with a UPS? Not having a UPS is an external threat on the reliability of the power grid.

      Doing a hard shutdown or tripping over power cords seem much likelier local scenarios than any spontaneous combustion of hardware components.