No effect of "size" in 'query' while reindexing in elasticsearch

Hello,
I have been using logstash to migrate a index to another. I have recently tried to reindex certain amount of data from large dataset in local environment. So I tried using following configuration for migration:

input{
elasticsearch{
hosts=> "localhost:9200"
index=> "old_index"
query=> '{"query":{"match_all":{}},"size":10 }'
}
}
filter {
mutate {
remove_field => [ "@version", "@timestamp"]
}
}
output{
elasticsearch{
hosts=>"localhost:9200"
index=>"new_index"
document_type=>"contact"
manage_template => false
document_id=>"%{contactId}"
}
}

But this reindexes all the documents in old_index to new_index, where as , I was expecting just 10 documents to be reindexed in new_index.
Am I missing some concept using logstash with elasticsearch?

I am having the exact same issue, did you get a solution?

Thanks