Elasticsearch node on 7.0 alpha is not booting (Upgrade from 6.1.2)

[shamzeer]

Elasticsearch version (bin/elasticsearch --version): 7.0.0 alpha1

Plugins installed: [analysis-phonetic, ingest-attachment]

JVM version (java -version): 1.8.0.181

OS version (uname -a if on a Unix-like system): Windows 2012 R2

Description of the problem including expected versus actual behavior: We have disabled "_all" field in our mappings in ElasticSearch 6.1.2. We have created indices and indexed data into it. The following is an example of the mapping.

{
"testindex": {
"mappings": {
"type": {
"_all": {
"enabled": false
},
"properties": {
"title": {
"type": "text"
},
"description": {
"type": "text"
}
}
}
}
}
}

Everything is fine with ElasticSearch 6.1.2. But when we upgrade to Elasticsearch 7.0.0 alpha 1, ElasticSearch boot up failed with the following error.

org.elasticsearch.index.mapper.MapperParsingException: Root mapping definition has unsupported parameters: [_all : {enabled=false}]

Is there a way to ignore it (_all) while booting up?
Or is there a way to update the mapping to remove the _all field?

Looking for a solution other than mandating re-index of data.

Please provide your suggestions. Thanks.

[elasticmachine]

Pinging @elastic/es-search

[dakrone]

Thanks for bringing this up @shamzeer, I'm working on a fix for this for 7.0

[shamzeer]

Thanks very much for considering this.

[dakrone]

Notes:

I originally thought we would be able to drop the _all mapping inside of DocumentMapperParser to work around the exception, however, this doesn't actually change the serialized value. What happens later is that then when we go to check if the mapping needs to be updated, the _all is still there in the compressed xcontent bytes, which causes the mapping to think it needs to be updated again, causing an assertion to trip.

My branch with the fix and unit test as well as rolling upgrade test (which fails) is at

master...dakrone:allow-underscore-all-in-mapping

[jpountz]

@dakrone The approach looks good to me. I would just ensure that enabled is actually false when removing _all from the map? Can you open a PR and assign me as a reviewer?

[jimczi]

@jpountz, we agreed with @dakrone that the @elastic/es-search team will handle this issue ;)
I'll open a new pr with the approach that @dakrone took and let's discuss the failing upgrade test there.