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https://issues.apache.org/jira/browse/SOLR-12413?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16494856#comment-16494856
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Gaël Jourdan edited comment on SOLR-12413 at 5/30/18 8:10 AM:
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Thanks for your feedback that this is a real issue.
[~elyograg], you're right, using Collections API would work. I did not mention
it but actually this problem occurs on a Solr cluster which is shutdown most of
the time because it's a backup cluster and we only start it in some emergency
cases. This is why we don't use Collections API.
was (Author: gjourdan):
[~elyograg], you're right, using Collections API would work. I did not mention
it but actually this problem occurs on a Solr cluster which is shutdown most of
the time because it's a backup cluster and we only start it in some emergency
cases. This is why we don't use Collections API.
> Solr ignores aliases.json from ZooKeeper at startup
> ---------------------------------------------------
>
> Key: SOLR-12413
> URL: https://issues.apache.org/jira/browse/SOLR-12413
> Project: Solr
> Issue Type: Bug
> Security Level: Public(Default Security Level. Issues are Public)
> Components: SolrCloud
> Affects Versions: 7.2.1
> Environment: A SolrCloud cluster with ZooKeeper (one node is enough
> to reproduce).
> Solr 7.2.1.
> ZooKeeper 3.4.6.
> Reporter: Gaël Jourdan
> Priority: Major
>
> Since upgrading to 7.2.1, we ran into an issue where Solr ignores
> _aliases.json_ file stored in ZooKeeper.
>
> +Steps to reproduce the problem:+
> # SolrCloud cluster is down
> # Direct update of _aliases.json_ file in ZooKeeper with Solr ZkCLI *without
> using Collections API* :
> ** {{java ... org.apache.solr.cloud.ZkCLI -zkhost ... -cmd clear
> /aliases.json}}
> ** {{java ... org.apache.solr.cloud.ZkCLI -zkhost ... -cmd put /aliases.json
> "new content"}}
> # SolrCloud cluster is started => _aliases.json_ not taken into account
>
> +Analysis:+
> Digging a bit in the code, what is actually causing the issue is that, when
> starting, Solr now checks for the metadata of the _aliases.json_ file and if
> the version metadata from ZooKeeper is lower or equal to local version, it
> keeps the local version.
> When it starts, Solr has a local version of 0 for the aliases but ZooKeeper
> also has a version of 0 of the file because we just recreated it. So Solr
> ignores ZooKeeper configuration and never has a chance to load aliases.
>
> Relevant parts of Solr code are:
> *
> [https://github.com/apache/lucene-solr/blob/branch_7_2/solr/solrj/src/java/org/apache/solr/common/cloud/ZkStateReader.java]
> : line 1562 : method setIfNewer
> {code:java}
> /**
> * Update the internal aliases reference with a new one, provided that its ZK
> version has increased.
> *
> * @param newAliases the potentially newer version of Aliases
> */
> private boolean setIfNewer(Aliases newAliases) {
> synchronized (this) {
> int cmp = Integer.compare(aliases.getZNodeVersion(),
> newAliases.getZNodeVersion());
> if (cmp < 0) {
> LOG.debug("Aliases: cmp={}, new definition is: {}", cmp, newAliases);
> aliases = newAliases;
> this.notifyAll();
> return true;
> } else {
> LOG.debug("Aliases: cmp={}, not overwriting ZK version.", cmp);
> assert cmp != 0 || Arrays.equals(aliases.toJSON(), newAliases.toJSON())
> : aliases + " != " + newAliases;
> return false;
> }
> }
> }{code}
> *
> [https://github.com/apache/lucene-solr/blob/branch_7_2/solr/solrj/src/java/org/apache/solr/common/cloud/Aliases.java]
> : line 45 : the "empty" Aliases object with default version 0
> {code:java}
> /**
> * An empty, minimal Aliases primarily used to support the non-cloud solr use
> cases. Not normally useful
> * in cloud situations where the version of the node needs to be tracked even
> if all aliases are removed.
> * A version of 0 is provided rather than -1 to minimize the possibility that
> if this is used in a cloud
> * instance data is written without version checking.
> */
> public static final Aliases EMPTY = new Aliases(Collections.emptyMap(),
> Collections.emptyMap(), 0);{code}
>
> Note that a workaround is to force ZooKeeper to always have a version greater
> than 0 for _aliases.json_ file (for instance by not clearing the file and
> just overwriting it again and again).
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