[jira] [Commented] (ZOOKEEPER-5090) SnapshotComparer includes ephemeral znodes in comparison output

["Sangeeta (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-5090?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18118196#comment-18118196 ] 

Sangeeta commented on ZOOKEEPER-5090:
-------------------------------------

Hi, I’d like to work on this issue.

I plan to update {{SnapshotComparer}} so nodes with a non-zero {{ephemeralOwner}} are excluded while the comparison tree is built, and add a regression test ensuring ephemeral paths and their payload sizes do not affect the comparison result.

Could this issue please be assigned to me?

Thank you.

> SnapshotComparer includes ephemeral znodes in comparison output
> ---------------------------------------------------------------
>
>                 Key: ZOOKEEPER-5090
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-5090
>             Project: ZooKeeper
>          Issue Type: Bug
>          Components: server
>    Affects Versions: 3.10.0
>         Environment: Operating system: Windows 11, amd64
> Java version: 17.0.12
> ZooKeeper version: 3.10.0-SNAPSHOT
> Branch: master
> Commit: 9102d0be12e66a5c592d8cbf0c6865f68ffa9252
>            Reporter: Salvatore Casolaro
>            Priority: Major
>
> SnapshotComparer includes ephemeral znodes in its comparison output, although its class documentation states that it only outputs information about permanent nodes and ignores both sessions and ephemeral nodes.
> The issue was reproduced on the Apache ZooKeeper master branch at commit
> 9102d0be12e66a5c592d8cbf0c6865f68ffa9252.
> h2. Expected behavior
> Znodes whose ephemeralOwner is non-zero should be excluded from the comparison data used by SnapshotComparer. Consequently, their paths and payload sizes should not appear in the reported differences or affect aggregate deltas.
> The official ZooKeeper 3.9.5 documentation states:
> {quote}This tool only outputs information about permanent nodes, ignoring both sessions and ephemeral nodes.
> {quote}
> Documentation:
> [ZooKeeper 3.9.5 documentation|https://zookeeper.apache.org/doc/r3.9.5/zookeeperTools.html#zkSnapshotComparer]
> h2. Actual behavior
> When two valid snapshots containing different ephemeral znodes are compared, SnapshotComparer reports the ephemeral paths as nodes found only in the left or right tree.
> The payload sizes of the ephemeral znodes are also included in the aggregate size calculations and affect the delta reported for the root node.
> Relevant output:
> {code:java}
> Node  found in both trees. Delta: -2 bytes, 0 descendants
> Node /effimero_sinistro found only in left tree. Descendant size: 13. Descendant count: 0
> Node /ephemeral_test found only in right tree. Descendant size: 11. Descendant count: 0
> All layers compared.
> {code}
> h2. Steps to reproduce
>  # Create a valid snapshot containing an ephemeral znode named /effimero_sinistro with a 13-byte payload.
>  # Create another valid snapshot containing an ephemeral znode named /ephemeral_test with an 11-byte payload.
>  # Verify with SnapshotFormatter that both nodes have a non-zero ephemeralOwner.
>  # Compare the snapshots using SnapshotComparer with both thresholds set to zero:
> {code:java}
> -l left_ephemeral.snap -r right_ephemeral.snap -b 0 -n 0
> {code}
> Observe that SnapshotComparer reports both ephemeral paths and includes their payload sizes in the aggregate root delta.
> h2. Snapshot evidence
> The dump of the left snapshot confirms:
> {code:java}
> /effimero_sinistro
> ephemeralOwner = 0x10000101fa30000
> dataLength = 13
> Session:
> 0x10000101fa30000, timeout = 30000, ephemeralCount = 1
> {code}
> The dump of the right snapshot confirms:
> {code:java}
> /ephemeral_test
> ephemeralOwner = 0x10000101fa30001
> dataLength = 11
> Session:
> 0x10000101fa30001, timeout = 30000, ephemeralCount = 1
> {code}
> Both ephemeralOwner values are non-zero and correspond to sessions stored in the respective snapshots.
> h2. Reproducibility
> The black-box regression test was first executed three times and failed consistently.
> The issue was subsequently reproduced on a verification branch based on
> upstream/master at the time of testing:
> {code:java}
> ZooKeeper version: 3.10.0-SNAPSHOT
> Branch: master
> Commit: 9102d0be12e66a5c592d8cbf0c6865f68ffa9252
> {code}
> SnapshotComparer completes the comparison successfully, but the regression test fails because the output contains the ephemeral znode path:
> {code:java}
> java.lang.AssertionError:
> Output must not contain: /effimero_sinistro
> {code}
> h2. Possible cause
> The issue appears to originate in TreeInfo.TreeNode.populateChildren().
> The method retrieves each DataNode and adds it to the internal TreeInfo without checking whether the node has a non-zero ephemeralOwner:
> {code:java}
> DataNode childNode = dataTree.getNode(childPath);
> long size;
> synchronized (childNode) {
>     size = childNode.data == null ? 0 : childNode.data.length;
> }
> TreeNode childTreeNode = new TreeNode(childPath, size);
> childTreeNode.populateChildren(childPath, dataTree, treeInfo, currentDepth + 1);
> children.add(childTreeNode);
> {code}
> As a result, ephemeral znodes are included in the internal comparison tree. Their paths can be reported directly, and their payload sizes can propagate to ancestor aggregates.
> In this reproduction, the 13-byte left ephemeral payload and the 11-byte right ephemeral payload produce the observed -2 byte delta for the root node.
> h2. Regression test
> A black-box JUnit 4 test invokes SnapshotComparer.main(String[]) with the two snapshot files. It verifies that the comparison completes successfully but does not include either ephemeral path in its output.
> The test is currently marked with @Ignore in the complete experimental test suite because it exposes the reported defect. The @Ignore annotation was temporarily removed when reproducing the failure.
> The relevant assertions are:
> {code:java}
> assertCompletedSuccessfully(result);
> assertOutputDoesNotContain(result, LEFT_EPHEMERAL_PATH);
> assertOutputDoesNotContain(result, RIGHT_EPHEMERAL_PATH);
> {code}
> The minimal snapshot files, sanitized snapshot dumps, and the complete
> regression test can be provided if needed.
> h2. Related issue
> SnapshotComparer was originally introduced in ZOOKEEPER-3427.
> I searched Jira and the Apache ZooKeeper GitHub repository for existing issues and pull requests concerning SnapshotComparer, ephemeral nodes, ephemeralOwner, permanent-node filtering, and session filtering, but I did not find an existing report covering this behavior.
> h2. Academic context
> This issue was identified while working on an academic software testing project provided within a course taught by Prof. Guglielmo De Angelis at the University of Rome Tor Vergata.
> GitHub profile: [Prof. Guglielmo De Angelis on GitHub|https://github.com/gulyx]



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