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RE: Announcing the @gridcoin.science Witness - STEM on STEEM

in #witness-category • 7 years ago (edited)

Why you need high availability? Can't you just make two witnesses and rely on the mesing/p2p capability of blockchain?
Also the fact that the daemon needs 20 Gibibytes of RAM makes me wonder if it is capable of scaling much over to what it is now.
See, I am not very positive. But Have an up-vote.

7 years ago in #witness-category by
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     7 years ago 

    No worries; your skepticism is valid.

    High availability is necessary because of a few things we noticed:

    • If the memory-mapped files are lost (usually to a reboot because they perform best when stored on a ramdisk), the entire blockchain will have to be replayed, which takes hours. Witnesses are expected to be reliable (i.e., not down for hours and missing blocks), so another instance is needed to take over.
    • Best practices for backup Steem witnesses currently dictate that there can only be one active daemon for a witness because if there were two (with the same private signing key), they could both try to stake a block. That is somehow problematic, but the reason doesn't appear to be documented, so we'll need to research this further.
    • Existing ways to detect failed primary daemons rely on checking for incremented missed blocks, which means a failure must have already happened before it's noticed.

    If we can come up with an active/active setup, witness failover would not be necessary, and perhaps it could almost eliminate missed blocks.

    Yes, the daemon needs many gibibytes of RAM, and that requirement is going to keep growing unless there's an overhaul of what gets loaded into RAM. For now, we must scale vertically.

    The use of zram is a mitigation that buys us quite a bit more time before we eventually run out of RAM. Hopefully a solution comes up before we need to upgrade physical RAM.

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