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https://issues.apache.org/jira/browse/SOLR-5381?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13809096#comment-13809096
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Noble Paul commented on SOLR-5381:
----------------------------------
OK ,
here is the plan to split clusterstate on a per collection basis
h2. How to use this feature?
Introduce a new option while creating a collection (external=true) . This will
keep the state of the collection in a separate node.
example :
http://localhost:8983/solr/admin/collections?action=CREATE&name=xcoll&numShards=5&replicationFactor=2&external=true
This will result in this following entry in clusterstate.json
{code:JavaScript}
{
“xcoll” : {“ex”:true}
}
{code}
there will be another ZK entry which carries the actual collection information
* /collections
** /xcoll
*** /state.json
{code:JavaScript}
{"xcoll":{
"shards":{"shard1":{
"range":”80000000-b332ffff”l,
"state":"active",
"replicas":{
"core_node1":{
"state":"active",
"base_url":"http://192.168.1.5:8983/solr";,
"core":"xcoll_shard1_replica1",
"node_name":"192.168.1.5:8983_solr",
"leader":"true"}}}},
"router":{"name":"compositeId"}}}
{code}
The main Overseer thread is responsible for creating collections and managing
all the events for all the collections in the clusterstate.json .
clusterstate.json is modified only when a collection is created/deleted or when
state updates happen to “non-external” collections
Each external collection to have its own Overseer queue as follows. There will
be a separate thread for each external collection.
* /collections
** /xcoll
*** /overseer
**** /collection-queue-work
**** /queue
**** /queue-work
h2. SolrJ enhancements
SolrJ would only listen to cluterstate,json. When a request comes for a
collection ‘xcoll’
* it would first check if such a collection exists
* If yes it first looks up the details in the local cache for that collection
* If not found in cache , it fetches the node /collections/xcoll/state.json and
caches the information
* Any query/update will be sent with extra query param specifying the
collection name , shard name and range (example
\_target_=xcoll:shard1:80000000-b332ffff) . A node would throw an error
(INVALID_NODE) if it does not the serve the collection/shard/range combo.
* If a SolrJ gets INVALID_NODE error it would invalidate the cache and fetch
fresh state information for that collection (and caches it again).
h2. Changes to each Solr Node
Each node would only listen to the clusterstate.json and the states of
collections which it is a member of. If a request comes for a collection it
does not serve, it first checks for the \_target_ param. All collections
present in the clusterstate.json will be deemed as collections it serves
* If the param is present and the node does not serve that
collection/shard/range combo, an INVALID_NODE error is thrown
** If the validation succeeds it is served
* If the param is not present and the node is a member of the collection, the
request is served by
** If the node is not a member of the collection, it uses SolrJ to proxy the
request to appropriate location
Internally , the node really does not care about the state of external
collections. If/when it is required, the information is fetched real time from
ZK and used and thrown away.
h2. Changes to admin GUI
External collections are not shown graphically in the admin UI .
> Split Clusterstate and scale
> -----------------------------
>
> Key: SOLR-5381
> URL: https://issues.apache.org/jira/browse/SOLR-5381
> Project: Solr
> Issue Type: Improvement
> Components: SolrCloud
> Reporter: Noble Paul
> Assignee: Noble Paul
> Original Estimate: 2,016h
> Remaining Estimate: 2,016h
>
> clusterstate.json is a single point of contention for all components in
> SolrCloud. It would be hard to scale SolrCloud beyond a few thousand nodes
> because there are too many updates and too many nodes need to be notified of
> the changes. As the no:of nodes go up the size of clusterstate.json keeps
> going up and it will soon exceed the limit impossed by ZK.
> The first step is to store the shards information in separate nodes and each
> node can just listen to the shard node it belongs to. We may also need to
> split each collection into its own node and the clusterstate.json just
> holding the names of the collections .
> This is an umbrella issue
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