Aggregation on parent/child documents

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Aggregation on parent/child documents

Augusto Uehara
Hello ElasticSearchers! 

I've been working on a BI system with ES 0.90 and we needed count "users" which have certain attributes, for instance let's say gender and star sign. A user is a parent-level document and the attributes are child documents. 

Fro the sample above, we were doing so by creating a query for each combination of male / female and the star signs and querying individually, as one can imagine, this was slow, but the results are exactly what we want. We could run this in roughly 2 minutes.

We considered using the msearch query to get these results in a single query and we ended up with something similar to this: https://gist.github.com/chaos-generator/9133118
The sample above runs in 40 seconds give or take.

And along came elastic search 1.0.0 and now we have aggregations, so we simplified our query to this: https://gist.github.com/chaos-generator/9133139
This runs lightning fast and we get the results in 200ms on average, which is ideal for us, BUT we get the total number of documents with the attributes, rather than the count on the parent documents.

Our problem, as you can see in the msearch gist, is that we have a parent level document and child documents, which would only be updated if another document with the exact same attributes came in, this means that a parent level user document can have three child documents that will have gender and star sign, but I only want to count the parent document, rather than each individual child document.

As we don't know in advance the attributes our users will be searching, we cannot use a script in index time to help us do this aggregation. We tried to use a script in search time like this:  https://gist.github.com/chaos-generator/9133321 , but it didn't work as we wanted too:

Any suggestions would be greatly appreciated.


Best regards,
Augusto

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Re: Aggregation on parent/child documents

Binh Ly
I'm wondering if the filter aggregation will work for you:

http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/search-aggregations-bucket-filter-aggregation.html

However, it does not support parent child, but if you have the children embedded directly inside the parent document, I think it should be similar in functionality to your _msearch solution.

BTW, if you are only doing aggregations or counts and don't really need search hits returned, you can further optimize by using the count search type:

_search?search_type=count

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Re: Aggregation on parent/child documents

Augusto Uehara
Thank you for your reply Binh,

I've tried the bucket filter, but had problems with parent/child relationships.

I've modified the multi-search query to use type = count, but the performance didn't change much, it took about 40 seconds to return the results. It was almost 20% faster indeed, but it is not the performance we want yet.

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Re: Aggregation on parent/child documents

Augusto Uehara
We run 4 instances of ES 1.0.0 using 30G for JVM. We run 64-bit OpenJDK 1.7.0_25 on ubuntu servers.

$ ulimit -a
core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 515139
max locked memory       (kbytes, -l) unlimited
max memory size         (kbytes, -m) unlimited
open files                      (-n) 64000
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 8192
cpu time               (seconds, -t) unlimited
max user processes              (-u) 515139
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

And I also disabled swap on linux.

You can use this gist to simulate the issue we have: https://gist.github.com/chaos-generator/9143655

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