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https://issues.apache.org/jira/browse/SOLR-1729?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12970785#action_12970785
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Peter Sturge commented on SOLR-1729:
------------------------------------

Many thanks for finishing off this patch. Sorry I didn't get time to fix this, 
been swamped with so many projects at the moment.
That's great you got the thread local NOW included as well. Thanks!


> Date Facet now override time parameter
> --------------------------------------
>
>                 Key: SOLR-1729
>                 URL: https://issues.apache.org/jira/browse/SOLR-1729
>             Project: Solr
>          Issue Type: Improvement
>          Components: search
>    Affects Versions: 1.4
>         Environment: Solr 1.4
>            Reporter: Peter Sturge
>            Priority: Minor
>             Fix For: 4.0
>
>         Attachments: FacetParams.java, SimpleFacets.java, 
> solr-1.4.0-solr-1729.patch, SOLR-1729.patch, SOLR-1729.patch, 
> SOLR-1729.patch, UnInvertedField.java
>
>
> This PATCH introduces a new query parameter that tells a (typically, but not 
> necessarily) remote server what time to use as 'NOW' when calculating date 
> facets for a query (and, for the moment, date facets *only*) - overriding the 
> default behaviour of using the local server's current time.
> This gets 'round a problem whereby an explicit time range is specified in a 
> query (e.g. timestamp:[then0 TO then1]), and date facets are required for the 
> given time range (in fact, any explicit time range). 
> Because DateMathParser performs all its calculations from 'NOW', remote 
> callers have to work out how long ago 'then0' and 'then1' are from 'now', and 
> use the relative-to-now values in the facet.date.xxx parameters. If a remote 
> server has a different opinion of NOW compared to the caller, the results 
> will be skewed (e.g. they are in a different time-zone, not time-synced etc.).
> This becomes particularly salient when performing distributed date faceting 
> (see SOLR-1709), where multiple shards may all be running with different 
> times, and the faceting needs to be aligned.
> The new parameter is called 'facet.date.now', and takes as a parameter a 
> (stringified) long that is the number of milliseconds from the epoch (1 Jan 
> 1970 00:00) - i.e. the returned value from a System.currentTimeMillis() call. 
> This was chosen over a formatted date to delineate it from a 'searchable' 
> time and to avoid superfluous date parsing. This makes the value generally a 
> programatically-set value, but as that is where the use-case is for this type 
> of parameter, this should be ok.
> NOTE: This parameter affects date facet timing only. If there are other areas 
> of a query that rely on 'NOW', these will not interpret this value. This is a 
> broader issue about setting a 'query-global' NOW that all parts of query 
> analysis can share.
> Source files affected:
> FacetParams.java   (holds the new constant FACET_DATE_NOW)
> SimpleFacets.java  getFacetDateCounts() NOW parameter modified
> This PATCH is mildly related to SOLR-1709 (Distributed Date Faceting), but as 
> it's a general change for date faceting, it was deemed deserving of its own 
> patch. I will be updating SOLR-1709 in due course to include the use of this 
> new parameter, after some rfc acceptance.
> A possible enhancement to this is to detect facet.date fields, look for and 
> match these fields in queries (if they exist), and potentially determine 
> automatically the required time skew, if any. There are a whole host of 
> reasons why this could be problematic to implement, so an explicit 
> facet.date.now parameter is the safest route.

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