Yury created SOLR-13315:
---------------------------
Summary: Possible SolrIndexSearcher leak through LogWatcher and
FunctionScoreQuery
Key: SOLR-13315
URL: https://issues.apache.org/jira/browse/SOLR-13315
Project: Solr
Issue Type: Bug
Security Level: Public (Default Security Level. Issues are Public)
Affects Versions: 7.5
Reporter: Yury
Attachments: path_to_gc_root_from_heap_dump.png
Here is possible leak of SolrIndexSearcher.
1) Where unused ref to SolrIndexSearcher is stored.
Log4j2Watcher implements LogWatcher<LogEvent>
and has CircularList<LogEvent> history inherited from LogWatcher<E>
In history we can store Log4jLogEvent which can hold ref to ParameterizedMessage
and ParameterizedMessage stores refs to all arguments of event log. (here we
can store objects which are no longer in use directly or indirectly)
2) How SolrIndexSearcher can be indirectly reached through this log buffer.
If during FunctionScoreQuery execution ExitingReaderException("The request took
too long to iterate over terms. Timeout: " ..) will be thrown this query will
be logged with warn level and it ref will be store in Log4j2Watcher.
(Here can be any exception which will log this query to Log4j2Watcher)
In general it should be ok but in this case FunctionScoreQuery indirectly
stores ref to SolrIndexSearcher.
As the result we have refs to already closed searchers which are no longer in
use.
Searcher has refs to caches (Docs, Filers, results ...) and they can not be
reclaimed by gc.
3) How SolrIndexSearcher can be accessed through FunctionScoreQuery
There is a FunctionScoreQuery which can hold ref to
MultiplicativeBoostValuesSource
which can hold ref to WrappedDoubleValuesSource
and the last one can hold ref to SolrIndexSearcher.
public final class FunctionScoreQuery extends Query {
...
private final DoubleValuesSource source;
...
}
private static class MultiplicativeBoostValuesSource extends DoubleValuesSource
{
private final DoubleValuesSource boost;
...
}
private static class WrappedDoubleValuesSource extends DoubleValuesSource {
private final ValueSource in;
private IndexSearcher searcher;
...
}
Actually any DoubleValuesSource implementation which stores ref to
IndexSearcher
on method call
public abstract DoubleValuesSource rewrite(IndexSearcher reader) throws
IOException;
can couse a problem if it will be logged via Log4j2Watcher.
4) How to temporary solve this problem
It is possible to disable Log4j2Watcher in solr.xml
5) How to fix this issue in more reliable way ?
I think that it is very dangerous to buffer refs to log messages arguments.
And may be Log4j2Watcher should be reworked to avoid buffering refs but
LoggingHandler depends on Log4j2Watcher.
But may be there are better ways to solve this issue.
Path to gc root is attached.
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