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https://issues.apache.org/jira/browse/SOLR-15859?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17650990#comment-17650990
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Michael Gibney commented on SOLR-15859:
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I think it might be possible (and preferable?) to implement this as a custom
{{SolrCache<K, V>}} implementation that wraps {{solr.CaffeineCache<K,
MetadataWrapper<V>>}}. I think [~ben.manes] was alluding to something like this
"MetadataWrapper" approach in his [comment above|#comment-17633401].
I've actually done something similar, and it can work quite well. It can be a
bit tricky, but I think the "per-entry stats" part would be pretty
straightforward done this way, and I really like the idea of implementing this
functionality without modifying the hot path of what's currently the
default/only cache implementation bundled with Solr. I think the only necessary
modification to the existing {{solr.CaffeineCache}} class would be to provide a
hook to actually dump the values, e.g., add them to a provided map, or
something (so as not to actually expose the internals)?
I do think the functionality you're pursuing with this could be useful. One
benefit of implementing as I'm suggesting above, I think this functionality
would be almost entirely pluggable (as in, plugins) -- aside from some
interface for actually dumping a snapshot of the contents of the cache, which I
suspect would indeed need a public method added to {{solr.CaffeineCache}}.
I would definitely recommend avoiding top-level {{synchronized (cache)}} -- and
I don't think that would be necessary if pursuing the "wrapping" approach.
Maybe a more tightly-scoped change that ignores for now the request handler and
stats tracking, and instead focuses on figuring out a clean (if perhaps
experimental?) method/interface for dumping the contents of
{{solr.CaffeineCache}}? I suspect that would be easier to merge with
confidence, and would open the door to iterate on different ways of achieving
some of the more nuanced functionality.
> 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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