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https://issues.apache.org/jira/browse/CASSANDRA-785?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12854086#action_12854086
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Jaakko Laine commented on CASSANDRA-785:
----------------------------------------
As discussed earlier in mailing list, load balancing cannot simply consider
primary range of bootstrap source when using rack aware (or DC shard) strategy,
but whole range (primary + replicas) need to be taken into account. Following
is a result of one test run using current LB functionality:
Address Status Load Range
Ring
146240099105929890127228403396377438645
192.168.0.104 Up 100.84 MB 573371861609767657238978844007740582
|<--|
192.168.0.101 Up 152.79 MB 37375360823777355034255131821084484487
| ^
192.168.0.102 Up 171.61 MB 78679861790617677332793962569191145101
v |
192.178.0.109 Up 688.97 MB 81901584797347486028896754414340634003
| ^
192.178.0.108 Up 21.22 MB 83864326228946960659296251414309936872
v |
192.168.1.107 Up 598.99 MB 89819165849860700111165509269175012567
| ^
192.168.1.106 Up 40.53 MB 98071312689481731589290075340406457109
v |
192.168.1.105 Up 65.89 MB 114171242327420423416372328565954705130
| ^
192.168.0.103 Up 250.74 MB 146240099105929890127228403396377438645
|-->|
As can be seen, the load is not exactly evenly balanced.
Attached patch gets bootstrap token according to the whole range of the
bootstrap source. Additionally, the token is adjusted locally in order to avoid
nodes in different racks from bootstrapping too close to each other. Almost
similar test run was done after the modifications and the final situation was:
Address Status Load Range
Ring
162707623323903830430688125027655118960
192.168.1.105 Up 187.56 MB 6397937533436544563999349762491808989
|<--|
192.178.0.108 Up 195.59 MB 22595489350255970966018220707106798316
| ^
192.168.0.101 Up 187.18 MB 37375360823777355034255131821084484487
v |
192.168.0.102 Up 241.7 MB 78679861790617677332793962569191145101
| ^
192.168.1.106 Up 305.2 MB 98034334071769068450923602160301798881
v |
192.178.0.109 Up 343.16 MB 107128436236301245608915524607283274430
| ^
192.168.0.104 Up 142.75 MB 114572714021825029937699759732741779443
v |
192.168.1.107 Up 134.35 MB 131133602853429031188902390794550667876
| ^
192.168.0.103 Up 129.2 MB 146240099105929890127228403396377438645
v |
192.178.0.110 Up 224.89 MB 162707623323903830430688125027655118960
|-->|
In this case nodes in different racks end up distributed much better in the
ring.
> Improve load balancing when using rack aware or DC strategy
> -----------------------------------------------------------
>
> Key: CASSANDRA-785
> URL: https://issues.apache.org/jira/browse/CASSANDRA-785
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Affects Versions: 0.5
> Reporter: Jaakko Laine
> Assignee: Jaakko Laine
> Fix For: 0.8
>
> Attachments: 785.patch
>
>
> Current load balancing functionality does not consider data centers. This may
> result in new nodes bootstrapping in "wrong" place if most loaded node is in
> another DC than the bootstrapping node. Explore possibilities to make load
> balance work better in multi-DC configuration without making load balancing
> complicated.
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