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Improve the robustness of old ZooKeeper log removal #1040

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Improve the robustness of old ZooKeeper log removal #1040

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Commits on Sep 27, 2024

  1. Improve the robustness of old ZooKeeper log removal 

    Motivation:

`OldLogRemover` in `ZooKeeperCommandExecutor` currently catches a
`Throwable` when deleting an old log or its log blocks. However, it has
two issues doing so:

- It doesn't handle an exception that's raised when reading the metadata
  of the old log.
- `Throwable` is way too wide exception to catch. Catching a
  `KeeperException` whose code is `NONODE` will be enough.
  - Note that the failure will only transfer the leadership to other
    replica, rather than stopping the whole replication process.

Modifications:

- `OldLogRemover` now catches `KeeperException` whose code is `NONODE`
  only.
- An attempt to read a missing log node's metadata is now handled
  properly.
- Added more detail to the log messages about missing nodes
  - Split `deleteLog()` into `deleteLog()` and `deleteLogBlock()`

Result:

- The leadership is not transferred anymore when `OldLogRemover`
  attempts to retrieve a missing log node's metadata, which is not
  really a critical issue.
  - Instead, the leadership will be transferred when an exception
    occurs not because of a missing node.
    @trustin
    trustin committed Sep 27, 2024
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  2. Lint

    @trustin
    trustin committed Sep 27, 2024
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