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https://issues.apache.org/jira/browse/SOLR-13807?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17179234#comment-17179234
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Michael Gibney commented on SOLR-13807:
---------------------------------------
aba1d18797c99b46edf211ff26b989a4d23f625b adds the ability to configure docset
domain size threshold ({{countCacheDf}} for consultation of the termFacetCache)
separately for base domain, fgSet, and bgSet. This is practically useful for
the common case where one might want to dedicate the termFacetCache primarily
to caching (large, static) bgSets, but accumulate facet counts for base and
fgSet "normally" (i.e., without consulting the termFacetCache). One nice
side-effect is that this allows the benchmarks above to demonstrate in a more
isolated way the different potential benefits from the termFacetCache wrt
sort-by-{{relatedness}}.
{code}
[magibney@mbp SOLR-13807-benchmarks]$ ./check.sh s true # no cache/cache
maxSize=0
cdnlty: 10 100 1k 10k 100k 1m
.1% 86 85 90 90 93 130
1% 89 87 92 91 96 138
10% 128 122 125 125 145 188
20% 145 137 142 143 162 242
30% 164 153 160 166 180 266
40% 186 176 180 180 201 295
50% 206 188 193 197 216 326
99.99% 198 196 200 200 220 332
[magibney@mbp SOLR-13807-benchmarks]$ ./check.sh s true # all caching disabled
at query level (countCacheDf=-1)
cdnlty: 10 100 1k 10k 100k 1m
.1% 88 86 91 89 94 121
1% 89 87 91 92 96 131
10% 124 122 127 126 146 186
20% 142 139 144 144 166 241
30% 160 156 162 160 213 264
40% 181 180 183 183 206 301
50% 196 195 197 196 216 324
99.99% 199 195 202 204 223 331
[magibney@mbp SOLR-13807-benchmarks]$ ./check.sh s true # bg-countCacheDf=0
(default; cache size->6 -- 1 per field)
cdnlty: 10 100 1k 10k 100k 1m
.1% 0 0 0 0 1 4
1% 1 1 1 2 5 8
10% 22 22 28 25 37 61
20% 42 42 43 44 59 99
30% 61 60 62 63 82 129
40% 80 80 84 84 101 165
50% 99 98 101 102 122 199
99.99% 122 118 123 124 142 231
[magibney@mbp SOLR-13807-benchmarks]$ ./check.sh s true # base, fg, bg
countCacheDf=0 (default; cache size->84)
cdnlty: 10 100 1k 10k 100k 1m
.1% 0 0 0 1 1 9
1% 0 0 0 1 4 12
10% 3 3 3 4 13 38
20% 6 6 6 7 14 47
30% 9 8 8 9 17 56
40% 11 10 11 10 21 64
50% 14 13 13 14 21 75
99.99% 25 24 24 25 34 108
{code}
The first two above demonstrate parity between disabling caching at the
collection config level and at the query level. The third illustrates the
result of consulting the termFacetCache only for the bgSet. The last consults
the termFacetCache across the board (base, fg, bg). One takeaway here is that
even a _very_ modestly-configured termFacetCache gives ~10x performance boost
for sort-by-skg against low-recall base domains, and a "worst"-case boost (for
high-cardinality domains) of ~33% -- and because of the static nature of the
bgSet, this boost can be expected to be consistent (unlike hit-or-miss gains
that are generally characteristic of caching).
The first two count-only benchmarks (below) demonstrates analogous parity for
different ways of disabled caching, and the third below shows significant
performance boost for count-only (sort-by-count) with default termFacetCache
consultation.
{code}
[magibney@mbp SOLR-13807-benchmarks]$ ./check.sh s count # no cache/maxSize=0
cdnlty: 10 100 1k 10k 100k 1m
.1% 0 0 0 0 0 4
1% 1 1 1 1 1 5
10% 9 8 9 8 11 15
20% 16 15 17 18 20 32
30% 23 21 23 22 26 42
40% 29 28 31 29 34 54
50% 37 34 37 35 41 65
99.99% 70 63 70 67 74 112
[magibney@mbp SOLR-13807-benchmarks]$ ./check.sh s count # caching disabled at
query time (countCacheDf=-1)
cdnlty: 10 100 1k 10k 100k 1m
.1% 0 0 0 0 0 4
1% 1 1 1 1 2 6
10% 7 8 8 9 11 14
20% 16 15 17 17 20 32
30% 23 21 22 21 27 42
40% 29 27 31 28 33 52
50% 35 33 39 35 43 63
99.99% 69 64 71 67 76 110
[magibney@mbp SOLR-13807-benchmarks]$ ./check.sh s count # countCacheDf=0
(default behavior; cache size->42)
cdnlty: 10 100 1k 10k 100k 1m
.1% 0 0 0 0 0 3
1% 0 0 0 0 1 4
10% 2 3 2 3 4 10
20% 6 6 6 6 7 13
30% 9 8 8 9 9 16
40% 12 11 11 12 13 19
50% 14 14 13 14 15 21
99.99% 27 25 26 25 27 35
{code}
> Caching for term facet counts
> -----------------------------
>
> Key: SOLR-13807
> URL: https://issues.apache.org/jira/browse/SOLR-13807
> Project: Solr
> Issue Type: New Feature
> Components: Facet Module
> Affects Versions: master (9.0), 8.2
> Reporter: Michael Gibney
> Priority: Minor
> Attachments: SOLR-13807-benchmarks.tgz,
> SOLR-13807__SOLR-13132_test_stub.patch
>
> Time Spent: 10m
> Remaining Estimate: 0h
>
> Solr does not have a facet count cache; so for _every_ request, term facets
> are recalculated for _every_ (facet) field, by iterating over _every_ field
> value for _every_ doc in the result domain, and incrementing the associated
> count.
> As a result, subsequent requests end up redoing a lot of the same work,
> including all associated object allocation, GC, etc. This situation could
> benefit from integrated caching.
> Because of the domain-based, serial/iterative nature of term facet
> calculation, latency is proportional to the size of the result domain.
> Consequently, one common/clear manifestation of this issue is high latency
> for faceting over an unrestricted domain (e.g., {{\*:\*}}), as might be
> observed on a top-level landing page that exposes facets. This type of
> "static" case is often mitigated by external (to Solr) caching, either with a
> caching layer between Solr and a front-end application, or within a front-end
> application, or even with a caching layer between the end user and a
> front-end application.
> But in addition to the overhead of handling this caching elsewhere in the
> stack (or, for a new user, even being aware of this as a potential issue to
> mitigate), any external caching mitigation is really only appropriate for
> relatively static cases like the "landing page" example described above. A
> Solr-internal facet count cache (analogous to the {{filterCache}}) would
> provide the following additional benefits:
> # ease of use/out-of-the-box configuration to address a common performance
> concern
> # compact (specifically caching count arrays, without the extra baggage that
> accompanies a naive external caching approach)
> # NRT-friendly (could be implemented to be segment-aware)
> # modular, capable of reusing the same cached values in conjunction with
> variant requests over the same result domain (this would support common use
> cases like paging, but also potentially more interesting direct uses of
> facets).
> # could be used for distributed refinement (i.e., if facet counts over a
> given domain are cached, a refinement request could simply look up the
> ordinal value for each enumerated term and directly grab the count out of the
> count array that was cached during the first phase of facet calculation)
> # composable (e.g., in aggregate functions that calculate values based on
> facet counts across different domains, like SKG/relatedness – see SOLR-13132)
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