From 6c0047c4304fc5cd84029996587d6ea1416d0578 Mon Sep 17 00:00:00 2001
From: antirez <antirez@gmail.com>
Date: Fri, 30 Sep 2011 18:41:25 +0200
Subject: [PATCH] redis-trib: better slots allocation strategy for resharding
---
src/redis-trib.rb | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/src/redis-trib.rb b/src/redis-trib.rb
index 083f9740..3717f54e 100755
--- a/src/redis-trib.rb
+++ b/src/redis-trib.rb
@@ -287,10 +287,22 @@ class RedisTrib
# instance.
def compute_reshard_table(sources,numslots)
moved = []
- sources.each{|s|
+ # Sort from bigger to smaller instance, for two reasons:
+ # 1) If we take less slots than instanes it is better to start getting from
+ # the biggest instances.
+ # 2) We take one slot more from the first instance in the case of not perfect
+ # divisibility. Like we have 3 nodes and need to get 10 slots, we take
+ # 4 from the first, and 3 from the rest. So the biggest is always the first.
+ sources = sources.sort{|a,b| b.slots.length <=> a.slots.length}
+ sources.each_with_index{|s,i|
# Every node will provide a number of slots proportional to the
# slots it has assigned.
- n = (numslots.to_f/4096*s.slots.length).ceil
+ n = (numslots.to_f/4096*s.slots.length)
+ if i == 0
+ n = n.ceil
+ else
+ n = n.floor
+ end
s.slots.keys.sort[(0...n)].each{|slot|
if moved.length < numslots
moved << {:source => s, :slot => slot}