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https://issues.apache.org/jira/browse/SOLR-15859?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17650996#comment-17650996
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Shawn Heisey commented on SOLR-15859:
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[~magibney] I'm not going to rule anything out that hasn't been carefully
considered. I fully admit that I am playing in a sandbox that has more
complexity than I am used to thinking about, so I doubt I can actually get this
done without some collaboration.
Anything that reduces or eliminates the amount of synchronization that I have
to worry about, especially if it actually makes the code simpler, is very
welcome. I never feel confident about code for a threaded environment where I
don't put some thought into thread safety issues, so I think I have a tendency
to overthink it.
I don't really mind if the cache dumper knows at least a little bit about the
internals it is dealing with, but the more that can be abstracted, the better.
I'm hoping to get to a point where it only knows about SolrCacheBase and
doesn't care about CaffeineCache. But obviously some work will be required in
the cache implementation to make that abstraction available.
I expect where the dumper will be most connected to other Solr/Lucene internals
is knowing how to dump each specific cache -- filterCache is very different
than queryResultCache.
What I envision with the dumper is initially making it an experimental feature.
I think it might be useful to have a section of the ref guide dedicated to
experimental features, where the API and internals of the feature may radically
change from release to release if a better approach is found. Maybe treat it a
little bit like the ASF does when incubating new projects.
> Add handler to dump filter cache
> --------------------------------
>
> Key: SOLR-15859
> URL: https://issues.apache.org/jira/browse/SOLR-15859
> Project: Solr
> Issue Type: Improvement
> Reporter: Andy Lester
> Assignee: Shawn Heisey
> Priority: Major
> Labels: FQ, cache, filtercache, metrics
> Attachments: cacheinfo-1.patch, cacheinfo-2.patch, cacheinfo.patch,
> fix_92_startup.patch
>
>
> It would be very helpful to be able to inspect the contents of the
> filterCache.
> I'd like to be able to query something like
> {{/admin/caches?type=filter&nentries=1000&sort=numHits+DESC}}
> nentries would be allowed to be -1 to get everything.
> It would be nice to see these data items for each entry. I don't know which
> are available, but I'm thinking blue sky here:
> * cache key, exactly as stored
> * Timestamp when the entry was inserted
> * Whether the insertion of the entry evicted another entry, and if so which
> one
> * Timestamp of when this entry was last hit
> * Number of hits on this entry forever
> * Number of hits on this entry over some time period
> * Number of documents matched by the filter
> * Number of bytes of memory used by the filter
> These are the sorts of questions I'd like to be able answer:
> * "I just did a query that I expect will have added a cache entry. Did it?"
> * "Are my queries hitting existing cache entries?"
> * "How big should I set my filterCache size? Should I limit it by number of
> entries or RAM usage?"
> * "Which of my FQs are getting used the most? These are the ones I want in
> my firstSearcher queries." (I currently determine this by processing my old
> solr logs)
> * "Which filters give me the most bang for the buck in terms of RAM usage?"
> * "I have filter X and filter Y, but would it be beneficial if I made a
> filter X AND Y?"
> * "Which FQs are used more at certain times of the day? (Assuming I take
> regular snapshots throughout the day)"
> I imagine a response might look like:
> {{{}}
> {{ "responseHeader": {}}
> {{ "status": 0,}}
> {{ "QTime": 961}}
> {{ },}}
> {{ "response": {}}
> {{ "numFound": 12104,}}
> {{ "filterCacheKeys": {}}
> {{ [}}
> {{ "language:eng": {}}
> {{ "inserted": "2021-12-04T07:34:16Z",}}
> {{ "lastHit": "2021-12-04T18:17:43Z",}}
> {{ "numHits": 15065,}}
> {{ "numHitsInPastHour": 2319,}}
> {{ "evictedKey": "agelevel:4 shippable:Y",}}
> {{ "numRecordsMatchedByFilter": 24328753,}}
> {{ "bytesUsed": 3041094}}
> {{ }}}
> {{ ],}}
> {{ [}}
> {{ "is_set:N": {}}
> {{ ...}}
> {{ }}}
> {{ ],}}
> {{ [}}
> {{ "language:spa": {}}
> {{ ...}}
> {{ }}}
> {{ ]}}
> {{ }}}
> {{}}}
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