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https://issues.apache.org/jira/browse/SOLR-13817?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16949630#comment-16949630
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Ben Manes commented on SOLR-13817:
----------------------------------
You might also want to review whether atomic computations (loading through the
cache) would provide a performance benefit. This is supported by Caffeine
(built on {{computeIfAbsent}}) and avoids performing costly redundant work. It
probably isn't worth the effort to implement it in the other caches if they are
eventually removed.
For example {{RptWithGeometrySpatialField}} and {{BlockJoinParentQParser}} show
classic patterns of a racy get-compute-put idiom:
{code}
SolrCache parentCache = request.getSearcher().getCache(CACHE_NAME);
// lazily retrieve from solr cache
Filter filter = null;
if (parentCache != null) {
filter = (Filter) parentCache.get(parentList);
}
BitDocIdSetFilterWrapper result;
if (filter instanceof BitDocIdSetFilterWrapper) {
result = (BitDocIdSetFilterWrapper) filter;
} else {
result = new BitDocIdSetFilterWrapper(createParentFilter(parentList));
if (parentCache != null) {
parentCache.put(parentList, result);
}
}
return result;
{code}
If multiple threads require the same key then they will observe have a cache
miss, perform an expensive call (or else why cached?), and insert their
results. By using {{computeIfAbsent}} style call, this will be performed by one
thread under a striped lock (hashbin lock) and the others will wait patiently
for the results. If it was present, in Caffeine's case, it will be a lock-free
read so there is no locking overhead. This avoids cache stampedes and can have
a performance impact under load.
> Deprecate legacy SolrCache implementations
> ------------------------------------------
>
> Key: SOLR-13817
> URL: https://issues.apache.org/jira/browse/SOLR-13817
> Project: Solr
> Issue Type: Improvement
> Security Level: Public(Default Security Level. Issues are Public)
> Reporter: Andrzej Bialecki
> Assignee: Andrzej Bialecki
> Priority: Major
>
> Now that SOLR-8241 has been committed I propose to deprecate other cache
> implementations in 8x and remove them altogether from 9.0, in order to reduce
> confusion and maintenance costs.
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