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From "Erick Erickson (JIRA)" <>
Subject [jira] [Commented] (SOLR-4083) Deprecate specifying individual <core> information in solr.xml. Possibly deprecate solr.xml entirely
Date Thu, 15 Nov 2012 17:00:13 GMT


Erick Erickson commented on SOLR-4083:

MMMMMooooommmmmm! He keeps bugging me <G>...

But maybe you've forced me to get to the core of the issue.

I _think_ the answer is that I don't know if it's acceptable to wait for startup until 10-15K
directories are enumerated and any associated properties files are examined (that's the scale
we're talking here). OTOH, I have no good intuition that it's _not_ acceptable. I was originally
thinking that the core information for large, complex installations could be kept in some
DB somewhere, or even in a special Solr "meta-data" core, and accessed on demand since there
is presumably a system-of-record for that information, possibly externally maintained. So
you could have a much faster startup in this case than if you had to enumerate a (very) large
tree structure.

You're right that in a situation where the (pluggable or not) coreDescriptorProvider walked
the directory structure anyway, there's no need to provide a way to plug anything, it'd take
the same amount of time either way. But what about other ways of storing this?

And I guess that _assuming_ an infrastructure is out there somewhere, I can argue that provisioning
the core (i.e. getting the directory created, getting the minimum directory structure in place
etc) has to be done outside of this mechanism anyway. Once a site solves that problem, just
walking the directory tree is sufficient, there's no need for additional coupling of the CoreDescriptorProvider
to the physical directory structure. Get the structure right and you'd automatically have
the info a CoreDescriptorProvider would return.

And I suppose one could spin off a thread at startup so startup would actually be very fast
at the expense of (possibly) waiting on your first core get until either 1> the directory
tree was exhausted or 2> the core was found.

Let me run an experiment or two to see what this looks like in practice. If it takes a minute
or two to start up, especially if loading core info is a background thread, I may be (finally)
forced to agree with you...
> Deprecate specifying individual <core> information in solr.xml. Possibly deprecate
solr.xml entirely
> ----------------------------------------------------------------------------------------------------
>                 Key: SOLR-4083
>                 URL:
>             Project: Solr
>          Issue Type: Improvement
>          Components: Schema and Analysis
>    Affects Versions: 4.1, 5.0
>            Reporter: Erick Erickson
>            Assignee: Erick Erickson
> Spinoff from SOLR-1306. Having a solr.xml file is limiting and possibly unnecessary.
We'd gain flexibility by having an "auto-discovery", essentially walking the directories and
finding all the cores and just loading them.
> Here's an issue to start the discussion of what that would look like. At this point the
way I'm thinking about it depends on SOLR-1306, which depends on SOLR-1028, so the chain is
getting kind of long.
> Straw-man proposal:
> 1> system properties can be specified as root paths in the solr tree to start discovery.
> 2> the directory walking process will stop going deep (but not wide) in the directories
whenever a file is encountered. That file can contain any of the properties
currently specifiable in a <core> tag. This allows, for instance, re-use of a single
solrconfig.xml or schema.xml file across multiple cores. I really dont want to get into having
cores-within-cores. While this latter is possible, I don't see any advantage. You _can_ have
multiple roots and there's _no_ requirement that the cores be in the directory immediately
below that root they can be arbitrarily deep.
> 3> I'm not quite sure what to do with the various properties in the <cores>
tag. Perhaps just require these to be system properties?
> 4> Notice the title. Does it still make sense to specify <3> in solr.xml but
ignore the cores stuff? It seems like so little information will be in solr.xml if we take
all the <core> tags out that we should just kill it all together.
> 5> Not quite sure what this means for _where_ the cores live. Is it arbitrary? Anywyere
on disk? Why not?
> 6> core swapping/renaming/whatever. Really, this is about how we model persist="true"
on solr.xml. It's easy if we keep solr.xml and just remove the individual core entries. Where
to put them?
> 7> _if_ we're supposed to persist core admin operations, it seems like we just persist
this stuff to the individual files. Things like whether it's loaded, whether
its name has changed (1028 allows lazy loading).
> 8> This still provide the capability of your own custom CoreDescriptorProvider, which
you'll have to specify somehow. I'm not quite sure where yet.
> solr.xml is really the bootstrap for the whole shootin' match. Removing it entirely means
we have to specify root directories, zk parameters, whatever somehow. What do people think
is the best option here? Leave a degenerate solr.xml? Require system properties be set for
any of these options? Currently, the options we'll need are anything (actual or proposed)
in the <solr> and <cores> tags.
> So, what the first cut at this would be, building on 1306, is a default CoreDescriptorProvider
that ignored all the <core> entries in solr.xml, walked the tree and loaded all the
cores found. I claim this is a quick thing to PoC assuming SOLR-1306 and I'll try to provide
a patch demonstrating it over the weekend.
> But mostly, this is a place to start the discussion about what this would look like rather
than have it get lost in SOLR-1306.
> finally, note that I have no intention of putting any of this into 4.x at least until
we cut the 4.1/4.0.1 whatever.
> And, of course, until we fully deprecate solr.xml (5.0?) the current behavior will be
the default.

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