Torsten Bøgh Köster created SOLR-10506:
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Summary: Possible memory leak upon collection reload
Key: SOLR-10506
URL: https://issues.apache.org/jira/browse/SOLR-10506
Project: Solr
Issue Type: Bug
Security Level: Public (Default Security Level. Issues are Public)
Components: Server
Affects Versions: 6.5
Reporter: Torsten Bøgh Köster
Upon manual Solr Collection reloading, references to the closed {{SolrCore}}
are not fully removed by the garbage collector as a strong reference to the
{{ZkIndexSchemaReader}} is held in a ZooKeeper {{Watcher}} that watches for
schema changes.
In our case, this leads to a massive memory leak as managed resources are still
referenced by the closed {{SolrCore}}. Our Solr cloud environment utilizes
rather large managed resources (synonyms, stopwords). To reproduce, we fired
out environment up and reloaded the collection 13 times. As a result we fully
exhausted our heap. A closer look with the Yourkit profiler revealed 13
{{SolrCore}} instances, still holding strong references to the garbage
collection root (see screenshot 1).
Each {{SolrCore}} instance holds a single path with strong references to the gc
root via a `Watcher` in `ZkIndexSchemaReader` (see screenshot 2). The
{{ZkIndexSchemaReader}} registers a close hook in the {{SolrCore}} but the
Zookeeper is not removed upon core close.
We supplied a Github Pull Request that extracts the zookeeper `Watcher` as a
static inner class. To eliminate the memory leak, the schema reader is held
inside a `WeakReference` and the reference is explicitly removed on core close.
Initially I wanted to supply a test case but unfortunately did not find a good
starting point ...
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