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https://issues.apache.org/jira/browse/SOLR-215?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12516192
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Hoss Man commented on SOLR-215:
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For the record, I have not looked at the most recent version of the patch --
don't think i've ever had a chance to look at any version of this patch
actually, but I since my fiance is currently reading harry potter, i figured
this was a good day to at least try and catch up on all the issue comments.
so far, i like what i'm reading -- i think the plan to first commit the
"framework" code so that multiple cores can be programmatic created, then
tackle the syntax for defining/creating/querying multiple cores via config
files and/or http params makes sense.
As far as the backwards compatibility issues go with things like the
Token(izer|Filter)Factory APIs, I think it's safe to say that people who want
to use multiple cores can be required to make minor modifications to custom
plugins they may have written in order to get them to work correctly with those
multiple cores.
what we have to watch out for is people who don't care about custom cores, and
have written custom plugins. things should continue to work for those people.
In the case of the token-blah-factories, a simple way to go (which can also
help us move away from the interface headache) might be to deprecate the
current factory interfaces, and add new abstract factory base classes which
implement those interfaces and are multi-core aware ... the initialization code
can first check to see if the class name in question extends the new abstract
base class -- if so then jolly good, if not then fall back to the legacy
behavior and init the class without any info about it's core.
the kind of situation i do worry about however is along the lines of a comment
Henri pointed out (very early on evidently, not sure how i missed it back
then)...
> Although the 'single core' feature has been retained (aka the static
> SolrCore.getCore),
> the SolrConfig.config could not;
...this is a little alarming, because there *may* be custom plugins that use
SolrConfig.config to get arbitrary configuration inforrmation from
solrconfig.xml ... i say *may* because we've never exactly advertised that as a
recommended technique, but that doesn't mean peope aren't doing it. At a
minimum we need a well documented replacement for (hopefully something like
SolrCore.getSolrCore(null).getSolrConfig() works) but the question that
immediately popped into my head was: "if SolrCore.getCore(null) can return 'the
null core' why can't SolrCOnfig.config be assigned the config from the null
core?"
In general, this is the kind of thing i worry about: making sure that any and
all custom plugin code that may exist right now can continue to exist and
function using a single core even after the multi-core functionality is
committed.
> Multiple Solr Cores
> -------------------
>
> Key: SOLR-215
> URL: https://issues.apache.org/jira/browse/SOLR-215
> Project: Solr
> Issue Type: Improvement
> Reporter: Henri Biestro
> Priority: Minor
> Attachments: solr-215.patch, solr-215.patch, solr-215.patch,
> solr-215.patch.zip, solr-215.patch.zip, solr-215.patch.zip,
> solr-215.patch.zip, solr-215.patch.zip, solr-215.patch.zip,
> solr-trunk-533775.patch, solr-trunk-538091.patch, solr-trunk-542847-1.patch,
> solr-trunk-542847.patch, solr-trunk-src.patch
>
>
> WHAT:
> As of 1.2, Solr only instantiates one SolrCore which handles one Lucene index.
> This patch is intended to allow multiple cores in Solr which also brings
> multiple indexes capability.
> The patch file to grab is solr-215.patch.zip (see MISC session below).
> WHY:
> The current Solr practical wisdom is that one schema - thus one index - is
> most likely to accomodate your indexing needs, using a filter to segregate
> documents if needed. If you really need multiple indexes, deploy multiple web
> applications.
> There are a some use cases however where having multiple indexes or multiple
> cores through Solr itself may make sense.
> Multiple cores:
> Deployment issues within some organizations where IT will resist deploying
> multiple web applications.
> Seamless schema update where you can create a new core and switch to it
> without starting/stopping servers.
> Embedding Solr in your own application (instead of 'raw' Lucene) and
> functionally need to segregate schemas & collections.
> Multiple indexes:
> Multiple language collections where each document exists in different
> languages, analysis being language dependant.
> Having document types that have nothing (or very little) in common with
> respect to their schema, their lifetime/update frequencies or even collection
> sizes.
> HOW:
> The best analogy is to consider that instead of deploying multiple
> web-application, you can have one web-application that hosts more than one
> Solr core. The patch does not change any of the core logic (nor the core
> code); each core is configured & behaves exactly as the one core in 1.2; the
> various caches are per-core & so is the info-bean-registry.
> What the patch does is replace the SolrCore singleton by a collection of
> cores; all the code modifications are driven by the removal of the different
> singletons (the config, the schema & the core).
> Each core is 'named' and a static map (keyed by name) allows to easily manage
> them.
> You declare one servlet filter mapping per core you want to expose in the
> web.xml; this allows easy to access each core through a different url.
> USAGE (example web deployment, patch installed):
> Step0
> java -Durl='http://localhost:8983/solr/core0/update' -jar post.jar solr.xml
> monitor.ml
> Will index the 2 documents in solr.xml & monitor.xml
> Step1:
> http://localhost:8983/solr/core0/admin/stats.jsp
> Will produce the statistics page from the admin servlet on core0 index; 2
> documents
> Step2:
> http://localhost:8983/solr/core1/admin/stats.jsp
> Will produce the statistics page from the admin servlet on core1 index; no
> documents
> Step3:
> java -Durl='http://localhost:8983/solr/core0/update' -jar post.jar ipod*.xml
> java -Durl='http://localhost:8983/solr/core1/update' -jar post.jar mon*.xml
> Adds the ipod*.xml to index of core0 and the mon*.xml to the index of core1;
> running queries from the admin interface, you can verify indexes have
> different content.
> USAGE (Java code):
> //create a configuration
> SolrConfig config = new SolrConfig("solrconfig.xml");
> //create a schema
> IndexSchema schema = new IndexSchema(config, "schema0.xml");
> //create a core from the 2 other.
> SolrCore core = new SolrCore("core0", "/path/to/index", config, schema);
> //Accessing a core:
> SolrCore core = SolrCore.getCore("core0");
> PATCH MODIFICATIONS DETAILS (per package):
> org.apache.solr.core:
> The heaviest modifications are in SolrCore & SolrConfig.
> SolrCore is the most obvious modification; instead of a singleton, there is a
> static map of cores keyed by names and assorted methods. To retain some
> compatibility, the 'null' named core replaces the singleton for the relevant
> methods, for instance SolrCore.getCore(). One small constraint on the core
> name is they can't contain '/' or '\' avoiding potential url & file path
> problems.
> SolrConfig (& SolrIndexConfig) are now used to persist all configuration
> options that need to be quickly accessible to the various components. Most of
> these variables were static like those found in SolrIndexSearcher. Mimicking
> the intent of these static variables, SolrConfig & SolrIndexConfig use public
> final members to expose them.
> SolrConfig inherits from Config which has been modified; Config is now more
> strictly a dom document (filled from some resource) and methods to evaluate
> xpath expressions. Config also continues to be the classloader singleton that
> allows to easily instantiate classes located in the Solr installation
> directory.
> org.apache.solr.analysis:
> TokenizerFactory & FilterFactory now get the SolrConfig passed as a parameter
> to init; one might want to read some resources to initialize the factory and
> the config dir is in the config. This is partially redundant with the
> argument map though.
> org.apache.solr.handler:
> RequestHandlerBase takes the core as a constructor parameter.
> org.apache.solr.util:
> The test harness has been modified to expose the core it instantiates.
> org.apache.solr.servlet:
> SolrDispatchFilter is now instantiating a core configured at init time; the
> web.xml must contain one filter declaration and one filter mapping per core
> you want to expose. Wherever some admin or servlet or page was referring to
> the SolrCore singleton or SolrConfig, they now check for the request
> attribute 'org.apache.solr.SolrCore' first; the filters set this attribute
> before forwarding to the other parts.
> Admin/servlet:
> Has been modified to use the core exposed through the request attribute
> 'org.apache.solr.SolrCore'.
> REPLICATION:
> The feature has not been implemented yet; the starting point is that instead
> of having just one index directory 'index/', the naming scheme for the index
> data directories is 'index*/'. Have to investigate.
> FUTURE:
> Uploading new schema/conf would be nice, allowing Solr to create cores
> dynamically; the upload mechanism itself is easy, the servlet dispatch filter
> needs to be modified.
> Having replication embedded in the Solr application itself using an http
> based version of the rsync algorithm; some of the core code of jarsync might
> be handy.
> MISC:
> The patch production process (not as easy as I thought it was with a
> Windows/Netbeans/cygwin/TortoiseSVN).
> 0/ Initial point is to have the modified code running in a local patch
> branch, all tests ok.
> 1/ Have one 'clean version' of the trunk aside the local patch branch; you'll
> need to verify that your patch can be applied to the last clean trunk version
> and that various tests still work from there. Creating the patch is key.
> 2/ If you used some IDE and forgot to set the auto-indentation corrrectly,
> you most likely need working around the space/indentation patch clutter that
> results. I could not find a way to get TortoiseSVN create a patch with the
> proper options (ignore spaces & al) and could not find a way to get
> NetbeansSVN generate one either. Thus I create the patch from the local trunk
> root through cygwin (with svn+patchutils); svn diff --diff-cmd /usr/bin/diff
> -x "-w -B -b -E -d -N -u" > ~/solr-215.patch.
> Before generating the patch, it is important to issue an 'svn add ...' for
> each file you might have added; a quick "svn status | grep '?'" allows to
> verify nothing will be missing. Not elegant, but you can even follow with:
> svn status | grep '?' | awk '{print $2}' | xargs svn add
> 3/ Apply the patch to the 'clean trunk'.
> TortoiseSVN 'apply patch' command only understands 'unified diff' thus the
> '-u' option.
> Alternatively, you can apply the patch through cygwin: patch -p0 -u <
> solr-215.patch.
> I've updated the 'dev' environment to an x86 Solaris 10 box which now
> generates the zipped patch( solr-215.patch.zip , same patch production
> method).
> For Solaris 10 users, patch must be "gnu" patch: /usr/local/bin/patch is its
> usual location (not to be confused with /bin/patch...)
> For x86, you can find it at
> ftp://ftp.sunfreeware.com/pub/freeware/intel/10/patch-2.5.4-sol10-x86-local.gz
> ; I don't know about diff but I'm using the version located at
> ftp://ftp.sunfreeware.com/pub/freeware/intel/10/diffutils-2.8.1-sol10-intel-local.gz
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