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From "Noble Paul (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (SOLR-6220) Replica placement startegy for solrcloud
Date Tue, 01 Jul 2014 15:07:24 GMT

     [ https://issues.apache.org/jira/browse/SOLR-6220?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Noble Paul updated SOLR-6220:
-----------------------------

    Summary: Replica placement startegy for solrcloud  (was: Replica placement startegy dor
solrcloud)

> Replica placement startegy 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
>
> 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&snitch.url=http://snitchserverhost:port?nodename={}}}
> The response of the  rest call   {{http://snitchserverhost:port/?nodename=192.168.1:8080_solr}}
> must be in either json format or properties format. 
> eg: 
> {code:JavaScript}
> {
> “tag-x”:”x-val”,
> “tag-y”:”y-val”
> }
> {code}
> or
> {noformat}
> tag-x=x-val
> tag-y=y-val
> {noformat}
> 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.Placement 
> 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 parameter  "placement" . The values will be saved in the state of the collection as follows
> {code:Javascript}
> {
>  “mycollection”:{
>   “snitch”: {
>       type:“EC2Snitch”
>     }
>   “placement”:{
>    “key1”: “value1”,
>    “key2”: “value2”,
>    }
> }
> {code}
> A rule consists of 2 parts
>  * LHS or the qualifier : The format is \{shardname}.\{replicacount} .    Use the wild
card “*” for qualifying all. Use the \(!) operand for exclusion
>  * RHS or  conditions :  The format is \{tagname}\{operand}\{value} . The tag name and
values are provided by the snitch. The supported operands are
>  ** -> :  equals
>  ** >    : greater than . Only applicable for numeric tags
>  **<     : less than , Only applicable to numeric tags
> 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
> Example rules:
>  * “shard1:1”:“dc->dc1&rack->168” : This would assign exactly 1 replica
for shard1 with nodes having tags   “dc=dc1,rack=168”.
>  *  “shard1:1+”:“dc->dc1&rack->168”  : Same as above but assigns atleast
one replica to the tag val combination
>  * “*.1”:“dc->dc1” :  For all shards keep exactly one replica in dc:dc1
>  * “*.1+”:”dc->dc2”  :     At least one  replica needs to be in dc:dc2
>  * “*.2-”:”dc->dc3” : Keep a maximum of 2 replicas in dc:dc3 for all shards
>  * “shard1.*”:”rack->730”  :  All replicas of shard1 will go to rack 730
>  * “shard1.1”:“node->192.167.1.2:8983_solr”  : 1 replica of shard1 must go
to the node 192.167.1.28983_solr
>  * “!shard1.* : “rack->738”  : No replica of shard1 should go to rack 738 
>  * “!shard1.* : “host->192.168.89.91”  : No replica of shard1 should go to host
192.168.89.91
> * “*.*”: “cores<5”: All replicas should be created in nodes with  less than
5 cores  
>  * “*.*”:”disk>20gb” :  All replicas must be created in nodes with disk space
greater than 20gb
> 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&placement=*.1:dc->dc1|*.2-:dc->dc3|!shard1. :rack->738

> {noformat}



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