[ZOOKEEPER-2789] Reassign `ZXID` for solving 32bit overflow problem

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 3.5.3
• Component/s: quorum
• Labels: pull-request-available
• Assignee: Benedict Jin
• Reporter: Benedict Jin
• Created: 23/May/17 01:45
• Updated: 05/Jan/23 06:27

Description

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.

Issue Links

• Blocked: ZOOKEEPER-1277 servers stop serving when lower 32bits of zxid roll over
• is related to: ZOOKEEPER-2791 Quorum doesn't recover after zxid rollover
• links to: GitHub Pull Request #262
• links to: GitHub Pull Request #262