Balancing primary shards


this is a very old topic, for which the answer is that balancing primary
shard is not useful,
mainly because indexing and replication cost more or less the same.

However, there is a case where it matters: percolation. Our elasticsearch
infrastructure is
composed of two nodes. Indexing incomming documents works like a charm, but
we also
have around 100 percolators, some of them involving fuzzy matches on
thousands strings.
Percolation requires a lot of cpu, a lot more than indexing.
There are very few search requests, thus their impact on the cpu is

We observe that, when all primary shards are gathered on one node (e.g.
badly balanced),
this node has a very high cpu load, while the other is just quiet. When
primary shards are
equally balanced, we observe a similar load on the two nodes.

#3293 has been updated (I cannot reopen it).


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