Why elasticsearch dynamic templates create explicit fields in the mapping? - elasticsearch

Question

The document that I want to index is as follows
{
"Under Armour": 0.16667,
"Skechers": 0.14774,
"Nike": 0.24404,
"New Balance": 0.11905,
"SONOMA Goods for Life": 0.11236
}
Fields under this node are dynamic, which means when documents are getting added various fields(brands) will come with those documents.
If I create an index without specifying a mapping, ES says "maximum number of fields (1000) have been reached". Though we can increase this value, it is not a good practice.
In order to support the above document, I created a mapping as follows and created an index.
{
"mappings": {
"my_type": {
"dynamic_templates": [
{
"template1":{
"match_mapping_type": "double",
"match": "*",
"mapping": {
"type": "float"
}
}
}
]
}
}
}
When I add above document to the created index and checked the mapping of the index again. It looks like as below.
{
"my_index": {
"mappings": {
"my_type": {
"dynamic_templates": [
{
"template1": {
"match": "*",
"match_mapping_type": "double",
"mapping": {
"type": "float"
}
}
}
],
"properties": {
"New Balance": {
"type": "float"
},
"Nike": {
"type": "float"
},
"SONOMA Goods for Life": {
"type": "float"
},
"Skechers": {
"type": "float"
},
"Under Armour": {
"type": "float"
}
}
}
}
}
}
If you clearly see the mapping that I created earlier and the mapping when I added a document to the index is different. It added fields statically added to the mapping. When I keep adding more documents, new fields will be added to the mapping (which will end up with maximum number of fields(1000) has been reached).
My question is,
The mapping that I mentioned above is correct for the above mentioned document.
If it is correct, why new fields are added to the mapping?

Answer 1

According to the posts that I read, increasing the number of fields in an index is not a good practice it may increase the resource usage.
In this case, when there are enormous number of brands are there and new brands to be introduced.
The proper solution for such a case is, introduce key-value pairs. (Probably I need to do a transformation during ETL)
{
"brands": [
{
"key": "Under Armour",
"value": 0.16667
},
{
"key": "Skechers",
"value": 0.14774
},
{
"key": "Nike",
"value": 0.24404
}
]
}
When the data is formatted as above, the map won't be change.
A good reading that I found was
https://www.elastic.co/blog/found-beginner-troubleshooting#keyvalue-woes
Thanks #Val for the suggestion