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https://issues.apache.org/jira/browse/ZOOKEEPER-2574?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15481129#comment-15481129
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Abhishek Rai commented on ZOOKEEPER-2574:
-----------------------------------------
Thanks [~phunt], I've uploaded a fix and unittest. Without the fix, the
unittest fails in the assertion below, thanks.
{noformat}
/**
* Verify that the last znode that was created above exists. This
znode's creation was
* captured by the transaction log which was created before any of the
above
* SNAP_RETAIN_COUNT snapshots were created, but it's not captured in
any of these
* snapshots. So for it it exist, the (only) existing log file should
not have been purged.
*/
final String lastZnode = "/snap-" + (unique - 1);
final Stat stat = zk.exists(lastZnode, false);
Assert.assertNotNull("Last znode does not exist: " + lastZnode, stat);
{noformat}
> PurgeTxnLog can inadvertently delete required txn log files
> -----------------------------------------------------------
>
> Key: ZOOKEEPER-2574
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2574
> Project: ZooKeeper
> Issue Type: Bug
> Components: server
> Affects Versions: 3.4.7, 3.4.8, 3.5.0, 3.5.1, 3.5.2
> Environment: Zookeeper 3.4.8, standalone, and 3-server quorum
> Reporter: Abhishek Rai
> Assignee: Abhishek Rai
> Priority: Blocker
> Fix For: 3.4.10, 3.5.3
>
> Attachments: ZOOKEEPER-2574.patch
>
>
> As part of the fix for ZOOKEEPER-1797, the call to
> FileTxnSnapLog.getSnapshotLogs() was removed from PurgeTxnLog.java. As a
> result, some old-looking but required txn log files can be deleted, resulting
> in data corruption or loss.
> For example, consider the following:
> 1. Configuration:
> autopurge.snapRetainCount=3
> 2. Following files exist:
> log.100 spans transactions from zxid=100 till zxid=140 (inclusive)
> snapshot.110 - snapshot as of zxid=110
> snapshot.120 - snapshot as of zxid=120
> snapshot.130 - snapshot as of zxid=130
> Above scenario is possible when snapshotting has happened multiple times but
> without accompanying log rollover, which is possible if the server was
> running as a learner.
> 3. PurgeTxnLog retains all snapshots but deletes log.100 because its zxid is
> older than the zxid of the oldest snapshot (110). This results in loss of
> transactions in the range 131-140.
> Before the fix for ZOOKEEPER-1797, this was avoided by the call to
> FileTxnSnapLog.getSnapshotLogs() which finds and retains the newest txn log
> file with starting zxid < oldest retained snapshot's highest zxid.
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