Do you guys know how to plug in a custom hash function for routing
parameter?
在 2014年3月26日星期三UTC+1下午12时51分24秒，Han JU写道：
>
> Thanks a lot Kevin.
>
> That DJB_HASH result makes it clear for us. I think we'll just use the id
> value as hash.
> Do you guys know how to plugin a custom hash function?
>
>
> 在 2014年3月26日星期三UTC+1上午11时58分36秒，Kevin Wang写道：
>>
>> There are two hash functions
>> implementation
>> org.elasticsearch.cluster.routing.operation.hash.djb.DjbHashFunction
>> and
>> org.elasticsearch.cluster.routing.operation.hash.simple.SimpleHashFunction,
>> default is DjbHashFunction. You can try get the hash by
>> using DjbHashFunction.DJB_HASH(you id)
>>
>>
>>
>>
>> On Wednesday, March 26, 2014 9:49:10 PM UTC+11, Han JU wrote:
>>>
>>> Thanks for your reply.
>>>
>>> As far as I know, in Java, basic hash value of positive int/long value
>>> is just themselves (our ids are small values like 1125, 345 etc).
>>> So I calculated some_id % 128, and I got 116 distinct values. But in
>>> reality there's a lot less shards in use.
>>>
>>> Does ElasticSearch use some special hash function?
>>>
>>> 在 2014年3月26日星期三UTC+1上午11时39分15秒，Kevin Wang写道：
>>>>
>>>> ES will get the shard id by hash(routing)%num of shards, in your case,
>>>> there are only 167 distinct values but have 128 shards, I think it's
>>>> highly
>>>> possible there is less than 128 distinct hash values. So some of the shard
>>>> will not have any data.
>>>>
>>>>
>>>> Kevin
>>>>
>>>> On Wednesday, March 26, 2014 9:30:36 PM UTC+11, Han JU wrote:
>>>>>
>>>>> Hi,
>>>>>
>>>>> We've indexed 25M documents into a single index of 128 shards with 1
>>>>> replica.
>>>>> The `routing` parameter is set to a path in the document, which is an
>>>>> int value:
>>>>>
>>>>> _routing: {
>>>>> path: "some_id"
>>>>> required: true
>>>>> }
>>>>>
>>>>>
>>>>> In out 25M documents, there's 167 distinct values of this "some_id"
>>>>> and in our expectation, ElasticSearch will route these documents evenly
>>>>> across all shards.
>>>>> But we've found out that, out of 128 shards, there are 53 empty shards
>>>>> (with 0 document inside), or, 40% of the shards are not used at all.
>>>>>
>>>>> My question:
>>>>>
>>>>> - is this normal? Do we miss something in configuring routing?
>>>>> - does this imbalanced shard utilization affect indexing speed?
>>>>>
>>>>> We can confirm that all documents are correctly indexed and routing
>>>>> works (when searching with routing only 1 shard responds with the correct
>>>>> answer).
>>>>> ElasticSearch version is v1.0.1.
>>>>>
>>>>>
>>>>> Thanks!
>>>>>
>>>>
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