Confusion over codec parameter to ILM force-merge action

[DaveCTurner]

In #49974 we added support for changing to the best_compression codec in ILM's force-merge action, but it seems that the parameter in the REST API is actually index_codec and not codec as per the docs:

elasticsearch/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ilm/ForceMergeAction.java

Line 36 in 95a7eed

public static final ParseField CODEC = new ParseField("index_codec");

This means the docs for 7.7 are wrong (see #55978). I think index_codec is an unfortunate choice of name and it would be preferable to change it to codec even though it's now a breaking change so we'd have to do the whole deprecation dance to achieve that.

[elasticmachine]

Pinging @elastic/es-core-features (:Core/Features/ILM+SLM)

[dakrone]

I think index_codec is an unfortunate choice of name and it would be preferable to change it to codec

I'm going to guess (since it was a community PR), that index_codec came from it being the index.codec setting, and I asked to not have a dot in the field name for the action definition.

Can you explain why you think index_codec is an unfortunate name? Just parity between the two?

[DaveCTurner]

Yes, just that I think of the index setting as simply codec (the namespace may be given separately and can even be omitted in some contexts) and that the index_ prefix seems redundant (whose codec could we be changing if not the index's?). I'm not certain we should rename it, but I do expect this discrepancy will catch me out in the future.

[zuozp8]

docs still need updating https://www.elastic.co/guide/en/elasticsearch/reference/7.7/ilm-forcemerge.html

[elasticmachine]

Pinging @elastic/es-docs (>docs)

[jrodewig]

#62243 updates the docs to use the current index_codec param name.

[jrodewig]

@dakrone @DaveCTurner I'm going to close this issue as the docs are now fixed. Please re-open if you feel we need to rename the parameter.