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https://issues.apache.org/jira/browse/SOLR-1729?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12805313#action_12805313
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Hoss Man commented on SOLR-1729:
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bq. (e.g. they are in a different time-zone, not time-synced etc.).
time-zones should be irrelevant since all calculations are done in UTC ... lack
of time-sync is a legitimate concern, but the more serious problem is
distributed requests and network lag. Even if all of the boxes have
synchronized clocks, they might not all get queried at the exact same time, and
multiple requets might be made to a single server for different phrases of the
distributed request that expect to get the same answers.
It should be noted that while adding support to date faceting for this type of
"when is now?" is certainly _necessary_ to make distributed date faceting work
sanely, it is not _sufficient_ ... unless filter queries that use date math
also respect it the counts returned from date faceting will still potentially
be non-sensical.
> 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
> Attachments: FacetParams.java, SimpleFacets.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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