Fwd: Deprecation of QueryElevationComponent's support for elevate.xml in data directories

[David Smiley <ds...@apache.org>]

---------- Forwarded message ---------
From: David Smiley <ds...@apache.org>
Date: Sat, Mar 20, 2021 at 12:36 AM
Subject: Deprecation of QueryElevationComponent's support for elevate.xml
in data directories
To: solr-user <so...@lucene.apache.org>
Cc: Bruno Roustant <br...@gmail.com>, Nazerke Seidan <
seinaz1997@gmail.com>, <mo...@europeana.eu>


Hey Solr community,

I found myself doing some maintenance inside QueryElevationComponent
related to some much larger refactoring.  I'm seeing a fair amount of
complexity around it's support of "elevate.xml" in a Solr *data* directory
(where the index is).  I don't know of any other Solr component that does
anything like this.  This feature of QEC existed from the start in Jan
2008.  In October of that same year, Solr's replication handler gained the
ability to replicate config files (see "confFiles" option) between cores.
I think this aspect of QEC would not have existed if it came later.  In
SolrCloud, you're expected to use ZooKeeper of course.

I plan to remove this mechanism in 9.0 on the grounds that it is obsolete.

To account for the ability to automatically detect elevate.xml changes in a
data dir and reload on a commit, I'm adding this mechanism to the
configSet/conf.  I'm not doing so for SolrCloud at this time because of
overhead concerns but it could be added later with some work.

I also plan to remove QEC's support of the elevate.xml file to be
"versioned" -- e.g. elevate.xml.001, elevate.xml.002.  The underlying
mechanism was added in
https://issues.apache.org/jira/browse/SOLR-351 where it was argued to be
useful for Windows OS which cannot replace an already open file.  Obviously
this is a non-issue in SolrCloud, and perhaps not an issue if you use the
confFiles replication feature to edit it either.  Regardless, I'm highly
suspicious it's an issue whatsoever since this file shouldn't be held open
on a sustained basis; it's only loaded on core load / replication and with
my changes above, on a commit if the modification time changes.

If you have concerns, let me know.

SOLR-15274 - QueryElevationComponent: auto-load file changes; remove data
dir support <https://issues.apache.org/jira/browse/SOLR-15274>

~ David Smiley
Apache Lucene/Solr Search Developer
http://www.linkedin.com/in/davidwsmiley