Wellington Chevreuil commented on HBASE-22618:

Hi [~PierreZ], yes, branch-1 is targeted for the next 1.x minor release, which 
happens to be 1.5 now. The next 1.4.y maintenance release is targeted to be 
1.4.11. To target this change to that release, we need to commit it on 
branch-1.4 as well. Maintenance releases should mostly concern to bug fixes, 
but since this improvement seems more like a new feature,  I'm wondering if it 
would be the right decision to include this in maintenance releases. 

{quote} * The second patch is missing, making the Jira not resolved. First 
patch was about opening the possibility to add cost functions, but we want to 
also provide an example of a cost function, by adding one that is allowing for 
Heterogeneous cluster, as stated by the ticket. Should I create another 
Yeah, let's keep things separate. Now that this Jira allows for adding custom 
cost functions, let's track custom cost functions development on its specific 
jira. Once you create this new jira, please link to this one.

> Provide a way to have Heterogeneous deployment
> ----------------------------------------------
>                 Key: HBASE-22618
>                 URL: https://issues.apache.org/jira/browse/HBASE-22618
>             Project: HBase
>          Issue Type: Improvement
>    Affects Versions: 3.0.0, 2.2.0, 2.2.1, 2.1.6, 1.4.11, 2.1.7
>            Reporter: Pierre Zemb
>            Assignee: Pierre Zemb
>            Priority: Major
>             Fix For: 3.0.0, 1.5.0, 2.3.0
>         Attachments: HBASE-22618.branch-1.001.patch, 
> HBASE-22618.branch-1.002.patch, HBASE-22618.branch-2.001.patch, 
> HBASE-22618.master.001.patch
> Hi,
> We wouls like to open the discussion about bringing the possibility to have 
> regions deployed on {color:#222222}Heterogeneous deployment{color}, i.e Hbase 
> cluster running different kind of hardware.
> h2. Why?
>  * Cloud deployments means that we may not be able to have the same hardware 
> throughout the years
>  * Some tables may need special requirements such as SSD whereas others 
> should be using hard-drives
>  * {color:#222222} {color}*in our usecase*{color:#222222}(single table, 
> dedicated HBase and Hadoop tuned for our usecase, good key 
> distribution){color}*, the number of regions per RS was the real limit for 
> us*{color:#222222}.{color}
> h2. Our usecase
> We found out that *in our usecase*(single table, dedicated HBase and Hadoop 
> tuned for our usecase, good key distribution)*, the number of regions per RS 
> was the real limit for us*.
> Over the years, due to historical reasons and also the need to benchmark new 
> machines, we ended-up with differents groups of hardware: some servers can 
> handle only 180 regions, whereas the biggest can handle more than 900. 
> Because of such a difference, we had to disable the LoadBalancing to avoid 
> the {{roundRobinAssigmnent}}. We developed some internal tooling which are 
> responsible for load balancing regions across RegionServers. That was 1.5 
> year ago.
> h2. Our Proof-of-concept
> We did work on a Proof-of-concept 
> [here|https://github.com/PierreZ/hbase/blob/dev/hbase14/balancer/hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/HeterogeneousBalancer.java],
>  and some early tests 
> [here|https://github.com/PierreZ/hbase/blob/dev/hbase14/balancer/hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/HeterogeneousBalancer.java],
> [here|https://github.com/PierreZ/hbase/blob/dev/hbase14/balancer/hbase-server/src/test/java/org/apache/hadoop/hbase/master/balancer/TestHeterogeneousBalancerBalance.java],
>  and 
> [here|https://github.com/PierreZ/hbase/blob/dev/hbase14/balancer/hbase-server/src/test/java/org/apache/hadoop/hbase/master/balancer/TestHeterogeneousBalancerRules.java].
>  We wrote the balancer for our use-case, which means that:
>  * there is one table
>  * there is no region-replica
>  * good key dispersion
>  * there is no regions on master
> A rule file is loaded before balancing. It contains lines of rules. A rule is 
> composed of a regexp for hostname, and a limit. For example, we could have:
> {quote}rs[0-9] 200
> rs1[0-9] 50
> {quote}
> RegionServers with hostname matching the first rules will have a limit of 
> 200, and the others 50. If there's no match, a default is set.
> Thanks to the rule, we have two informations: the max number of regions for 
> this cluster, and the rules for each servers. {{HeterogeneousBalancer}} will 
> try to balance regions according to their capacity.
> Let's take an example. Let's say that we have 20 RS:
>  * 10 RS, named through {{rs0}} to {{rs9}} loaded with 60 regions each, and 
> each can handle 200 regions.
>  * 10 RS, named through {{rs10}} to {{rs19}} loaded with 60 regions each, and 
> each can support 50 regions.
> Based on the following rules:
> {quote}rs[0-9] 200
> rs1[0-9] 50
> {quote}
> The second group is overloaded, whereas the first group has plenty of space.
> We know that we can handle at maximum *2500 regions* (200*10 + 50*10) and we 
> have currently *1200 regions* (60*20). {{HeterogeneousBalancer}} will 
> understand that the cluster is *full at 48.0%* (1200/2500). Based on this 
> information, we will then *try to put all the RegionServers to ~48% of load 
> according to the rules.* In this case, it will move regions from the second 
> group to the first.
> The balancer will:
>  * compute how many regions needs to be moved. In our example, by moving 36 
> regions on rs10, we could go from 120.0% to 46.0%
>  * select regions with lowest data-locality
>  * try to find an appropriate RS for the region. We will take the lowest 
> available RS.
> h2. Other implementations and ideas
> Clay Baenziger proposed this idea on the dev ML:
> {quote}{color:#222222}Could it work to have the stochastic load balancer use 
> [pluggable cost functions instead of this static list of cost 
> functions|[https://github.com/apache/hbase/blob/baf3ae80f5588ee848176adefc9f56818458a387/hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/StochasticLoadBalancer.java#L198]]?
>  Then, could this type of a load balancer be implemented simply as a new cost 
> function which folks could choose to load and mix with the others?{color}
> {quote}
> {color:#222222}I think this could be an interesting way to include 
> user-functions in the mix. As you know your hardawre and the pattern access, 
> you can easily know which metrics is important for balancing, for us, it will 
> only be the number of regions, but we could mix-it with the incoming 
> writes!{color}
> bhupendra.jain proposed also the ideas of "labels"
> {quote}{color:#222222}Internally, we are also having discussion to develop 
> similar solution. In our approach, We were also thinking of adding "RS Label" 
> Feature similar to Hadoop Node Label feature. {color}
> {color:#222222}Each RS can have a label to denote its capabilities / 
> resources . When user create table, there can be extra attributes with its 
> descriptor. The balancer can decide to host region of table based on RS label 
> and these attributes further.  {color}
>  {color:#222222}With RS label feature, Balancer can be more intelligent.  
> Example tables with high read load needs more cache backed by SSDs , So such 
> table regions should be hosted on RS having SSDs ... {color}
> {quote}
> {color:#222222}I love the idea, but I think Clay's idea is better for a 
> better and faster first set of commits on the subject! What do you think? 
> {color}

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