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https://issues.apache.org/jira/browse/SOLR-6349?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14091534#comment-14091534
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Hoss Man commented on SOLR-6349:
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Proposed implementation...
* Change StatsValuesFactory.createStatsValues (and the constructors for the
various StatsValues impls) to take in the local params from the {{stats.field}}
* each StatsValue impl should validate the stat params it's asked to compute
* all stats should default to disabled, but we need a special backcompat case
that if *no* stats are specified in local param, all current default stats are
computed
** we can't be lazy and just check 0==localparams.size() - need to check the
actuals stats params because of local params like "ex" and "key"
* for the distributed logic where things get a bit more complex (ie: distrib
mean needs sum+count from all shards; distrib stddev needs
sum+count+sumOfSquares from each shard) we can go two possible routes:
** A) StatsValue needs a new method to be *asked* by StatsComponent what local
params it needs when sending shard requests
*** in this case the localparams of the shard requests have diff localparams
and the processing of those shard stats requests can be ignorant of the fact
that they are distributed
** B) StatsValue (via the factory method) needs to be informed when it's
computing stats for an "isShard" request, so it can internally decide what
per-shard values to return based on the input
*** in this case, the localparams are not modified per shard, but since
"isShard=true" the StatsValue may return diff metrics then the ones requested
so that the coordinator gets what it needs to aggregate.
** I think i'm leaning towards option "B" - particularly because it simplifies
the idea of how to deal with situations like "percentiles" where the per-shard
info isn't really a stat that should have it's own localparma folks migth ask
for.
* deprecate {{stats.calcdistinct}} but use it as a default for the new
corresponding localparam(s)
> LocalParams for enabling/disabling individual stats
> ---------------------------------------------------
>
> Key: SOLR-6349
> URL: https://issues.apache.org/jira/browse/SOLR-6349
> Project: Solr
> Issue Type: Sub-task
> Reporter: Hoss Man
>
> Stats component currently computes all stats (except for one) every time
> because they are relatively cheap, and in some cases dependent on eachother
> for distrib computation -- but if we start layering stats on other things it
> becomes unnecessarily expensive to compute all the stats when they just want
> the "sum" (and it will definitely become excessively verbose in the
> responses).
> The plan here is to use local params to make this configurable. All of the
> existing stat options could be modeled as a simple boolean param, but future
> params (like percentiles) might take in a more complex param value...
> Example:
> {noformat}
> stats.field={!min=true max=true percentiles='99,99.999'}price
> stats.field={!mean=true}weight
> {noformat}
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