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https://issues.apache.org/jira/browse/ZOOKEEPER-2325?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15713016#comment-15713016
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ASF GitHub Bot commented on ZOOKEEPER-2325:
-------------------------------------------
Github user hanm commented on a diff in the pull request:
https://github.com/apache/zookeeper/pull/117#discussion_r90516950
--- Diff:
src/java/main/org/apache/zookeeper/server/persistence/FileTxnSnapLog.java ---
@@ -165,8 +165,22 @@ public File getSnapDir() {
*/
public long restore(DataTree dt, Map<Long, Integer> sessions,
PlayBackListener listener) throws IOException {
- snapLog.deserialize(dt, sessions);
+ long deserializeResult = snapLog.deserialize(dt, sessions);
FileTxnLog txnLog = new FileTxnLog(dataDir);
+ if (-1L == deserializeResult) {
+ /* this means that we couldn't find any snapshot, so we need to
+ * initialize an empty database */
+ if (txnLog.getLastLoggedZxid() != -1) {
+ throw new IOException(
+ "No snapshot found, but there are log entries. " +
+ "Something is broken!");
+ }
+ /* TODO: (br33d) we should either put a ConcurrentHashMap on
restore()
+ * or use Map on save() */
+ save(dt, (ConcurrentHashMap<Long, Integer>)sessions);
--- End diff --
I think we need it here because if we are getting here then the zxid of
this server must be -1, so it would not win leader election if at least one
other server is sane (with valid snapshot/txn log to recover.), so this server
will become a follow and sync the (none empty) snapshot from the leader. If all
servers have empty snapshots then this save is also required to bootstrap the
recover process.
> Data inconsistency if all snapshots empty or missing
> ----------------------------------------------------
>
> Key: ZOOKEEPER-2325
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2325
> Project: ZooKeeper
> Issue Type: Bug
> Components: server
> Affects Versions: 3.4.6
> Reporter: Andrew Grasso
> Assignee: Andrew Grasso
> Priority: Critical
> Attachments: ZOOKEEPER-2325-test.patch, ZOOKEEPER-2325.001.patch,
> zk.patch
>
> Original Estimate: 1h
> Remaining Estimate: 1h
>
> When loading state from snapshots on startup, FileTxnSnapLog.java ignores the
> result of FileSnap.deserialize, which is -1L if no valid snapshots are found.
> Recovery proceeds with dt.lastProcessed == 0, its initial value.
> The result is that Zookeeper will process the transaction logs and then begin
> serving requests with a different state than the rest of the ensemble.
> To reproduce:
> In a healthy zookeeper cluster of size >= 3, shut down one node.
> Either delete all snapshots for this node or change all to be empty files.
> Restart the node.
> We believe this can happen organically if a node runs out of disk space.
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