Merge policy settings are ignored when set in YML

[pickypg]

Setting the merge_factor, and other merge policies, from within the YML file are always overridden by the defaults. There is a workaround, which is to set them in a base index template, which will cause them to be taken. This is only an issue in 1.4.0 and 1.4.1.

This came up when trying to set index.merge.policy.merge_factor in elasticsearch.yml to a value other than 10, which is the default. Peaking at the code, the sibling settings are also effected (e.g., index.merge.policy.max_merge_size).

For example, in an elasticsearch.yml:

index.merge.policy.type: log_byte_size 
index.merge.policy.merge_factor: 30 

After creating any index, you will see something along the lines of

[2014-12-10 00:00:00,920][INFO ][cluster.metadata   ] [cluster-name] [index-name-2014.12.10] creating index, cause [auto(bulk api)], shards [4]/[2], mappings [] 
[2014-12-10 00:00:03,664][INFO ][index.merge.policy ] [cluster-name] [index-name-2014.12.10][3] updating merge_factor from [30] to [10]

Notice that it's reverting the merge_factor (and it's not just a mistake in the log output).

All of the providers suffer the from the same issue:

• LogDocMergePolicyProvider
• LogByteSizeMergePolicyProvider
• TieredMergePolicyProvider

They all get the value set at index-creation time -- defaulting it to the global default if it's unset -- then compare to see if it's different from the global value. If they're different, it uses the index-creation value, which means the global default if it is unset.

The fix is simple, the passed in "default" should just be the global value rather than the global default.