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From "Peter Sturge (JIRA)" <j...@apache.org>
Subject [jira] Created: (SOLR-1729) Date Facet now override time parameter
Date Thu, 21 Jan 2010 16:21:54 GMT
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


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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