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From Chet Aldrich <chet.aldr...@postmates.com>
Subject Re: Does ElasticsearchIO in the latest RC support adding document IDs?
Date Wed, 15 Nov 2017 19:08:56 GMT
Given that this seems like a change that should probably happen, and I’d like to help contribute
if possible, a few questions and my current opinion: 

So I’m leaning towards approach B here, which is:
> b. (a bit less user friendly) PCollection<KV> with K as an id. But forces the user
to do a Pardo before writing to ES to output KV pairs of <id, json>
> 
I think that the reduction in user-friendliness may be outweighed by the fact that this obviates
some of the issues surrounding a failure when finishing a bundle. Additionally, this forces
the user to provide a document id, which I think is probably better practice. This will also
probably lead to fewer frustrations around “magic” code that just pulls something in if
it happens to be there, and doesn’t if not. We’ll need to rely on the user catching this
functionality in the docs or the code itself to take advantage of it. 

IMHO it’d be generally better to enforce this at compile time because it does have an effect
on whether the pipeline produces duplicates on failure. Additionally, we get the benefit of
relatively intuitive behavior where if the user passes in the same Key value, it’ll update
a record in ES, and if the key is different then it will create a new record. 

Curious to hear thoughts on this. If this seems reasonable I’ll go ahead and create a JIRA
for tracking and start working on a PR for this. Also, if it’d be good to loop in the dev
mailing list before starting let me know, I’m pretty new to this. 

Chet 

> On Nov 15, 2017, at 12:53 AM, Etienne Chauchot <echauchot@apache.org <mailto:echauchot@apache.org>>
wrote:
> 
> Hi Chet,
> 
> What you say is totally true, docs written using ElasticSearchIO will always have an
ES generated id. But it might change in the future, indeed it might be a good thing to allow
the user to pass an id. Just in 5 seconds thinking, I see 3 possible designs for that. 
> a.(simplest) use a json special field for the id, if it is provided by the user in the
input json then it is used, auto-generated id otherwise.
> 
> b. (a bit less user friendly) PCollection<KV> with K as an id. But forces the user
to do a Pardo before writing to ES to output KV pairs of <id, json>
> 
> c. (a lot more complex) Allow the IO to serialize/deserialize java beans and have an
String id field. Matching java types to ES types is quite tricky, so, for now we just relied
on the user to serialize his beans into json and let ES match the types automatically.
> 
> Related to the problems you raise bellow:
> 
> 1. Well, the bundle is the commit entity of beam. Consider the case of ESIO.batchSize
being < to bundle size. While processing records, when the number of elements reaches batchSize,
an ES bulk insert will be issued but no finishBundle. If there is a problem later on in the
bundle processing before the finishBundle, the checkpoint will still be at the beginning of
the bundle, so all the bundle will be retried leading to duplicate documents. Thanks for raising
that! I'm CCing the dev list so that someone could correct me on the checkpointing mecanism
if I'm missing something. Besides I'm thinking about forcing the user to provide an id in
all cases to workaround this issue.
> 2. Correct.
> 
> Best,
> Etienne
> 
> Le 15/11/2017 à 02:16, Chet Aldrich a écrit :
>> Hello all! 
>> 
>> So I’ve been using the ElasticSearchIO sink for a project (unfortunately it’s
Elasticsearch 5.x, and so I’ve been messing around with the latest RC) and I’m finding
that it doesn’t allow for changing the document ID, but only lets you pass in a record,
which means that the document ID is auto-generated. See this line for what specifically is
happening: 
>> 
>> https://github.com/apache/beam/blob/master/sdks/java/io/elasticsearch/src/main/java/org/apache/beam/sdk/io/elasticsearch/ElasticsearchIO.java#L838
<https://github.com/apache/beam/blob/master/sdks/java/io/elasticsearch/src/main/java/org/apache/beam/sdk/io/elasticsearch/ElasticsearchIO.java#L838>

>> 
>> Essentially the data part of the document is being placed but it doesn’t allow
for other properties, such as the document ID, to be set. 
>> 
>> This leads to two problems: 
>> 
>> 1. Beam doesn’t necessarily guarantee exactly-once execution for a given item in
a PCollection, as I understand it. This means that you may get more than one record in Elastic
for a given item in a PCollection that you pass in. 
>> 
>> 2. You can’t do partial updates to an index. If you run a batch job once, and then
run the batch job again on the same index without clearing it, you just double everything
in there. 
>> 
>> Is there any good way around this? 
>> 
>> I’d be happy to try writing up a PR for this in theory, but not sure how to best
approach it. Also would like to figure out a way to get around this in the meantime, if anyone
has any ideas. 
>> 
>> Best, 
>> 
>> Chet
>> 
>> P.S. CCed echauchot@gmail.com <mailto:echauchot@gmail.com> because it seems
like he’s been doing work related to the elastic sink. 
>> 
>> 
> 


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