On May 1 a user started generating transactions with many inputs (presumably “sweeping” up Zcash that was stored in many different addresses of theirs). These transactions have increased the computational and network load, and this has caused problems for some users. Reported problems include Zcash nodes using more RAM (potentially exceeding the RAM available and crashing), transactions taking longer to confirm, and a higher orphan rate causing losses to miners.
We’ve investigated and determined that there’s no reason to think anyone is behaving maliciously, and there’s no evidence that any security vulnerability exists.
We’re adding additional monitoring to help us understand how the live network is behaving (orphan rates, RAM usage of Zcash nodes, transaction time-to-confirm, etc.). We’re also adding more benchmarks which exercise this code inside our Continuous Integration system so that we can optimize the Zcash software to handle this load better.
We have the following recommendations for users:
• Provision 8 GB of RAM for Zcash full nodes.
• Take into account that calls to getblocktemplate may take up to 15 seconds to complete when the blockchain is under load.
• Don’t treat a transaction as final until the transaction has 10 confirmations (which typically takes about half an hour after the transaction is posted).
• If you experience any difficulties, either with the performance issues described here or anything else “weird” or problematic, contact us! Join the Zcash community chat (https://chat.zcashcommunity.com) and ask for support.