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From "Peter Sturge (JIRA)" <j...@apache.org>
Subject [jira] Commented: (SOLR-1729) Date Facet now override time parameter
Date Wed, 03 Feb 2010 12:01:29 GMT

    [ https://issues.apache.org/jira/browse/SOLR-1729?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12829043#action_12829043
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Peter Sturge commented on SOLR-1729:
------------------------------------

Hi Chris,
Thanks for your comments - I hope I didn't sound like your comments were taken wrongly - I
absolutely count on comments from you and other experts to make sure I'm not missing some
important functionality and/or side effect. You know the code base far better than I, so its
great that you take the time to point out all the different bits and peices that need addressing.

I can certainly understand the need to address the 'core-global' isssues raised by you and
Yonik for storing a ThreadLocal 'query-global' 'NOW'.
I suppose the main issue in implementing the thread-local route is that we'd have to make
sure we found every place in the query core that references now, and point those references
to the new variable? If the 'code-at-large' [hopefully] always calls the date math routines
for finding 'NOW', great, it should be relatively straightforward. If there are any stray
e.g. System.currentTimeMillis(), then it's a bit more fiddly, but still do-able.

??it's all handled internally by DateField??
Sounds like DateField would the best candidate for holding the ThreadLocal? The query handler
code can set the variable of its DateField instance if it's set in a query parameter, otherwise
it just defaults to it's own local (UTC) time.
Could be done similarly to DateField.ThreadLocalDateFormat, perhaps?


> 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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