The next step for T166733: Deploy refactored comment storage is to finally remove most of the old comment fields. Before we can drop them in WMF production, we'll have to make the following changes to the WMCS views.
Non-compat view field removals:
- archive: Remove ar_comment
- archive_userindex: Remove ar_comment
- filearchive:
- Remove fa_deleted_reason
- Remove fa_description
- filearchive_userindex:
- Remove fa_deleted_reason
- Remove fa_description
- image: Remove img_description
- ipblocks: Remove ipb_reason.
- ipblocks_ipindex: Remove ipb_reason.
- logging: Remove log_comment.
- logging_logindex: Remove log_comment.
- logging_userindex: Remove log_comment.
- oldimage: Remove oi_description
- oldimage_userindex: Remove oi_description
- recentchanges: Remove rc_comment.
- recentchanges_userindex: Remove rc_comment.
- revision: Remove rev_comment.
- revision_userindex: Remove rev_comment.
Compat field changes:
- archive_compat: (no changes)
- filearchive_compat:
- Change the alias for fa_deleted_reason to just comment_a.comment_text as fa_deleted_reason.
- Change the alias for fa_description to just if(fa_deleted&2,NULL,comment_b.comment_text) as fa_description.
- image_compat: Change the alias for img_description to just comment_text as img_description.
- ipblocks_compat: Change the alias for ipb_reason to just comment_text as ipb_reason.
- logging_compat: Change the alias for log_comment to just if(log_deleted&2,null,comment_text) as log_comment.
- oldimage_compat: Change the alias for oi_description to just if(oi_deleted&2,null,comment_text) as oi_description.
- protected_titles_compat: Change the alias for pt_reason to just comment_text as pt_reason.
- recentchanges_compat: Change the alias for rc_comment to just if(rc_deleted&2,null,comment_text) as rc_comment.
- revision_compat: Change the alias for rev_comment to just if(rev_deleted&2,null,comment_text) as rev_comment.
You might also change the various LEFT JOINs with the comment table in the compat views to be (INNER) JOINs instead, to more closely match what MediaWiki is going to be doing. On the other hand, leaving them as LEFT shouldn't hurt anything.
The end result should be no change in user-visible behavior for the compat views, as everything should already be hitting the comment_text cases, while users using the non-compat views will start getting errors about nonexistent fields if they haven't already updated their code to join with comment.