[
https://issues.apache.org/jira/browse/SOLR-8297?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15981797#comment-15981797
]
Shikha Somani commented on SOLR-8297:
-------------------------------------
The proposal mentioned is fine except one point i.e. 'check that fromField and
toField are router.keys in these collections'. This condition will hinder cases
when routing key is different from toField/fromField. There are practical
use-cases when these keys can be different. This will add SQL like restriction
that join can be applied only on foreign key and foreign key has to be the
primary key of the other collection.
Attached is an new enhanced patch:
* Ready for master branch (Solr 7)
* Adhering to proposal
* Improved test cases and well tested
* Taking ‘rangeCheck’ in raw parameters as well as in local parameters. This
enables to join multiple (more than 2) collections having a mixed bag of
composite and implicit collection
** eg - toCol (composite), fromComposite (composite), fromImplicit (implicit)
** Applying join between these 3 collections, is now supported with this new
patch
> Allow join query over 2 sharded collections: enhance functionality and
> exception handling
> -----------------------------------------------------------------------------------------
>
> Key: SOLR-8297
> URL: https://issues.apache.org/jira/browse/SOLR-8297
> Project: Solr
> Issue Type: Improvement
> Components: SolrCloud
> Affects Versions: 5.3
> Reporter: Paul Blanchaert
> Attachments: SOLR-8297_Latest.patch, SOLR-8297.patch
>
>
> h2. Proposal
> h3. General Idea
> Approach [~shikhasomani]'s range check algorithm to the most cases
> h3. Join behavior depending on router types of joined collections
> || to\\from ||CompositeId||Implicit||
> ||CompositeId| shard range check, see table below | allow |
> ||Implicit| allow | shard to shard |
> h3. CompositeId to CompositeId join behaviour for certain number of shards
>
> || to\\from ||single||>1||
> ||single| allow (as is) | allow (range check) |
> ||>1| allow (as is) | per shard range check |
> h3. Rules from the tables above
> * joining from/to CompositeId and Implicit is blindly allowed, it pick ups
> any collocated replica, because users who do that probably understand what
> they do.
> * when both sides are Implicit let's join shards by name. ie if request hits
> collectionTO_shardY_replica2 at a node, the collocated
> collectionFROM_shardY_replica* is expected.
> * when both sides are CompositeId
> ** from single shard to single shard - nobrainer, just needs collocated
> replica;
> ** from multiple shards to single shard - all "from" shards (any it's
> replicas) are picked for joining
> ** from single shard to multiple shards - existing SOLR-4905 functionality
> ** from multiple to multiple - generic range check algorithm
> ### check that fromField and toField are router.keys in these collections
> ### take shard range for the current "to" collection replica (keep in mind
> that request is distributed across "to" collection shards)
> ### enumerate "from" collection shrads, find their subset which covers "to"
> shard range (this allows to handle any number of shards at both sides)
> ### pickup collocated replicas of these "from" shard subset
> h3. Caveat
> this is quite sensitive to shard allocation (and/or replica placement) ie
> failed "from" replica cannot be collocated with the required "to" shard.
> h2. Initial Description
> Enhancement based on SOLR-4905. New Jira issue raised as suggested by Mikhail
> Khludnev.
> A) exception handling:
> The exception "SolrCloud join: multiple shards not yet supported" thrown in
> the function findLocalReplicaForFromIndex of JoinQParserPlugin is not
> triggered correctly: In my use-case, I've a join on a facet.query and when my
> results are only found in 1 shard and the facet.query with the join is
> querying the last replica of the last slice, then the exception is not thrown.
> I believe it's better to verify the nr of slices when we want to verify the
> "multiple shards not yet supported" exception (so exception is thrown when
> zkController.getClusterState().getSlices(fromIndex).size()>1).
> B) functional enhancement:
> I would expect that there is no problem to perform a cross-core join over
> sharded collections when the following conditions are met:
> 1) both collections are sharded with the same replicationFactor and numShards
> 2) router.field of the collections is set to the same "key-field" (collection
> of "fromindex" has router.field = "from" field and collection joined to has
> router.field = "to" field)
> The router.field setup ensures that documents with the same "key-field" are
> routed to the same node.
> So the combination based on the "key-field" should always be available within
> the same node.
> From a user perspective, I believe these assumptions seem to be a "normal"
> use-case in the cross-core join in SolrCloud.
> Hope this helps
--
This message was sent by Atlassian JIRA
(v6.3.15#6346)
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
