[
https://issues.apache.org/jira/browse/SOLR-9524?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15497213#comment-15497213
]
Mike Drob commented on SOLR-9524:
---------------------------------
Chatted with [~mbraun688] about this a bit...
I think {{computeIfAbsent}} is close to what we want, but it doesn't let us
easily preserve the current behaviour to throw {{IOException}} - we'd have to
wrap it as an RTE. I'm also a little sceptical of the claim that multiple
threads would be attempting to calculate the same fingerprint, since this is
only called when we open a new searcher.
I'll agree that it may be expensive, but I don't what code paths we are trying
to protect against. And I think we'd get much better gains by doing the
optimizations at the lower level... There's a note in IndexFingerprint that
{{// TODO: this could be parallelized, or even cached per-segment if
performance becomes an issue}}, which I think is where we should look instead
of trying to ensure that a fingerprint is only calculated once.
If we _do_ need to ensure that each fingerprint is only calculated once for
performance issues, then we should switch to a more granular locking mechanism.
Possibly something like striped locking, or a parallel Map<Long, Lock>. This is
a lot more complexity.
> SolrIndexSearcher.getIndexFingerprint uses dubious sunchronization
> ------------------------------------------------------------------
>
> Key: SOLR-9524
> URL: https://issues.apache.org/jira/browse/SOLR-9524
> Project: Solr
> Issue Type: Bug
> Security Level: Public(Default Security Level. Issues are Public)
> Affects Versions: 6.3
> Reporter: Mike Drob
>
> In SOLR-9310 we added more code that does some fingerprint caching in
> SolrIndexSearcher. However, the synchronization looks like it could be made
> more efficient and may have issues with correctness.
> https://github.com/apache/lucene-solr/blob/branch_6x/solr/core/src/java/org/apache/solr/search/SolrIndexSearcher.java#L2371-L2385
> Some of the issues:
> * Double checked locking needs use of volatile variables to ensure proper
> memory semantics.
> * sync on a ConcurrentHashMap is usually a code smell
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
---------------------------------------------------------------------
To unsubscribe, e-mail: dev-unsubscr...@lucene.apache.org
For additional commands, e-mail: dev-h...@lucene.apache.org
