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https://issues.apache.org/jira/browse/SOLR-6220?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Noble Paul updated SOLR-6220:
-----------------------------
Attachment: SOLR-6220.patch
First cut with some basic tests
> Replica placement strategy for solrcloud
> ----------------------------------------
>
> Key: SOLR-6220
> URL: https://issues.apache.org/jira/browse/SOLR-6220
> Project: Solr
> Issue Type: Bug
> Components: SolrCloud
> Reporter: Noble Paul
> Assignee: Noble Paul
> Attachments: SOLR-6220.patch
>
>
> h1.Objective
> Most cloud based systems allow to specify rules on how the replicas/nodes of
> a cluster are allocated . Solr should have a flexible mechanism through which
> we should be able to control allocation of replicas or later change it to
> suit the needs of the system
> All configurations are per collection basis. The rules are applied whenever a
> replica is created in any of the shards in a given collection during
> * collection creation
> * shard splitting
> * add replica
> * createsshard
> There are two aspects to how replicas are placed: snitch and placement.
> h2.snitch
> How to identify the tags of nodes. Snitches are configured through collection
> create command with the snitch prefix . eg: snitch.type=EC2Snitch.
> The system provides the following implicit tag names which cannot be used by
> other snitches
> * node : The solr nodename
> * host : The hostname
> * ip : The ip address of the host
> * cores : This is a dynamic varibale which gives the core count at any given
> point
> * disk : This is a dynamic variable which gives the available disk space at
> any given point
> There will a few snitches provided by the system such as
> h3.EC2Snitch
> Provides two tags called dc, rack from the region and zone values in EC2
> h3.IPSnitch
> Use the IP to infer the “dc” and “rack” values
> h3.NodePropertySnitch
> This lets users provide system properties to each node with tagname and value
> .
> example : -Dsolrcloud.snitch.vals=tag-x:val-a,tag-y:val-b. This means this
> particular node will have two tags “tag-x” and “tag-y” .
>
> h3.RestSnitch
> Which lets the user configure a url which the server can invoke and get all
> the tags for a given node.
> This takes extra parameters in create command
> example: {{snitch={type=RestSnitch,url=http://snitchserverhost:port/[node]}}
> The response of the rest call
> {{http://snitchserverhost:port/?nodename=192.168.1:8080_solr}}
> must be in json format
> eg:
> {code:JavaScript}
> {
> “tag-x”:”x-val”,
> “tag-y”:”y-val”
> }
> {code}
> h3.ManagedSnitch
> This snitch keeps a list of nodes and their tag value pairs in Zookeeper. The
> user should be able to manage the tags and values of each node through a
> collection API
> h2.Rules
> This tells how many replicas for a given shard needs to be assigned to nodes
> with the given key value pairs. These parameters will be passed on to the
> collection CREATE api as a multivalued parameter "rule" . The values will be
> saved in the state of the collection as follows
> {code:Javascript}
> {
> “mycollection”:{
> “snitch”: {
> type:“EC2Snitch”
> }
> “rules”:[
> {“shard”: “value1”, “replica”: “value2”, "tag1":"val1"},
> {“shard”: “value1”, “replica”: “value2”, "tag2":"val2"}
> ]
> }
> {code}
> A rule is specified as a pseudo JSON syntax . which is a map of keys and
> values
> *Each collection can have any number of rules. As long as the rules do not
> conflict with each other it should be OK. Or else an error is thrown
> * In each rule , shard and replica can be omitted
> ** default value of replica is {{\*}} means ANY or you can specify a count
> and an operand such as {{+}} or {{-}}
> ** and the value of shard can be a shard name or {{\*}} means EACH or
> {{**}} means ANY. default value is {{\*\*}} (ANY)
> * There should be exactly one extra condition in a rule other than {{shard}}
> and {{replica}}.
> * all keys other than {{shard}} and {{replica}} are called tags and the tags
> are nothing but values provided by the snitch for each node
> * By default certain tags such as {{node}}, {{host}}, {{port}} are provided
> by the system implicitly
> Examples:
> {noformat}
> //in each rack there can be max two replicas of A given shard
> {rack:*,shard:*,replica:2-}
> //in each rack there can be max two replicas of ANY replica
> {rack:*,shard:**,replica:2-}
> {rack:*,replica:2-}
> //in each node there should be a max one replica of EACH shard
> {node:*,shard:*,replica:1-}
> //in each node there should be a max one replica of ANY shard
> {node:*,shard:**,replica:1-}
> {node:*,replica:1-}
>
> //In rack 738 and shard=shard1, there can be a max 0 replica
> {rack:738,shard:shard1,replica:0-}
>
> //All replicas of shard1 should go to rack 730
> {shard:shard1,replica:*,rack:730}
> {shard:shard1,rack:730}
> // all replicas must be created in a node with at least 20GB disk
> {replica:*,shard:*,disk:20+}
> {replica:*,disk:20+}
> {disk:20+}
> // All replicas should be created in nodes with less than 5 cores
> //In this ANY AND each for shard have same meaning
> {replica:*,shard:**,cores:5-}
> {replica:*,cores:5-}
> {cores:5-}
> //one replica of shard1 must go to node 192.168.1.2:8080_solr
> {node:”192.168.1.2:8080_solr”, shard:shard1, replica:1}
> //No replica of shard1 should go to rack 738
> {rack:!738,shard:shard1,replica:*}
> {rack:!738,shard:shard1}
> //No replica of ANY shard should go to rack 738
> {rack:!738,shard:**,replica:*}
> {rack:!738,shard:*}
> {rack:!738}
> {noformat}
> In the collection create API all the placement rules are provided as a
> parameter called placement and multiple rules are separated with "|"
> example:
> {noformat}
> snitch={type:EC2Snitch}&rule={shard:*,replica:1,dc:dc1}&rule={shard:*,replica:2-,dc:dc3}&rule{shard:shard1,replica:*,rack:!738}
>
> {noformat}
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