Gaël Jourdan created SOLR-12413:
-----------------------------------
Summary: 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
Since upgrading to 7.2.1, we ran into an issue where Solr ignores aliases.json
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
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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