[jira] [Created] (SOLR-15859) Add handler to dump filter cache

["Andy Lester (Jira)" <ji...@apache.org>]

Andy Lester created SOLR-15859:
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             Summary: Add handler to dump filter cache
                 Key: SOLR-15859
                 URL: https://issues.apache.org/jira/browse/SOLR-15859
             Project: Solr
          Issue Type: Improvement
      Security Level: Public (Default Security Level. Issues are Public)
            Reporter: Andy Lester


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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