sijie opened a new pull request #847: BP-23: Ledger Balancer (WIP)
URL: https://github.com/apache/bookkeeper/pull/847
 
 
   Descriptions of the changes in this PR:
   
   In Messaging/Streaming/Logging oriented use case (where old ledgers/segments 
are most likely will be deleted at some point), we don't actually need to 
rebalance the ledgers stored on bookies.
   
   However,
   In Storage oriented use cases (where data most likely will never be 
deleted), BookKeeper data might not always be placed uniformly across bookies. 
One common reason is addition of new bookies to an existing cluster. This 
proposal is proposing to provide a balancer mechanism (as an utility, also as 
part of AutoRecovery daemon), that analyzes ledger distributions and balances 
ledgers across bookies.
   
   It replicated ledgers to new bookies (based on resource-aware placement 
policies) until the cluster is deemed to be balanced, which means that disk 
utilization of every bookie (ratio of used space on the node to the capacity of 
the node) differs from the utilization of the cluster (ratio of used space on 
the cluster to total capacity of the cluster) by no more than a given threshold 
percentage.
   
   The balancer will replicate ledgers away from disk-filled bookies as first 
priority.
   
   Master Issue: #846 
   

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