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ASF GitHub Bot commented on ZOOKEEPER-2789: ------------------------------------------- Github user yunfan123 commented on the issue: https://github.com/apache/zookeeper/pull/262 Hi, I think 48 bits low is better for large throughput zk cluster. Another benefits is when use 48 bits low we assuming the epoch low than (1<<16), so we can 16 bits high to judge whether it is old version or new version. So use 48 bits low we can make the upgrade progress smoothly > Reassign `ZXID` for solving 32bit overflow problem > -------------------------------------------------- > > Key: ZOOKEEPER-2789 > URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2789 > Project: ZooKeeper > Issue Type: Bug > Components: quorum > Affects Versions: 3.5.3 > Reporter: Benedict Jin > Assignee: Benedict Jin > Fix For: 3.6.0 > > Original Estimate: 168h > Remaining Estimate: 168h > > If it is `1k/s` ops, then as long as $2^32 / (86400 * 1000) \approx 49.7$ > days ZXID will exhausted. But, if we reassign the `ZXID` into 16bit for > `epoch` and 48bit for `counter`, then the problem will not occur until after > $Math.min(2^16 / 365, 2^48 / (86400 * 1000 * 365)) \approx Math.min(179.6, > 8925.5) = 179.6$ years. > However, i thought the ZXID is `long` type, reading and writing the long type > (and `double` type the same) in JVM, is divided into high 32bit and low 32bit > part of the operation, and because the `ZXID` variable is not modified with > `volatile` and is not boxed for the corresponding reference type (`Long` / > `Double`), so it belongs to [non-atomic operation] > (https://docs.oracle.com/javase/specs/jls/se8 /html/jls-17.html#jls-17.7). > Thus, if the lower 32 bits of the upper 32 bits are divided into the entire > 32 bits of the `long`, there may be a concurrent problem. -- This message was sent by Atlassian JIRA (v6.4.14#64029)