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Message Sharing Migration

Part of the message sharing project.

Assumptions

• message-sharing-populate has run.
• Codebase is fully message-sharing-enabled.
• Schema elements that are to be removed are either gone or no longer used.

Code changes

To be landed before migration:

• Define TranslationMessage.converge():

  1. Look for TM "shared" with same (potmsgset, language, COALESCE(variant, -1), msgstr0, ...) as self, where shared.potemplate is null.

  2. If found: delete self.

  3. If not found: self.potemplate = NULL.

• When clearing is_imported in validate_is_imported or is_current in validate_is_current, converge the TM that's having the flag cleared if it ends up being neither imported nor current.

Migration steps

Migration consists of these phases:

• Initial Cleanup

• Merge POTMsgSets

• Converge TranslationMessages

Initial Cleanup

Before migrating, we should delete all non-current POTemplates. This eliminates some complications in migration.

Before we can delete a POTemplate, we must delete any rows that refer to it:

1. Clear TranslationMessage.pofile if the column still exists. We won't be using it anymore.

2. Delete all TranslationMessages that refer to the template in their potemplate fields.

3. Find all TranslationTemplateItems that refer to the template, and delete them.

4. Find any POTMsgSets that the deleted TranslationTemplateItems referred to, and that have no other TranslationTemplateItems referring to them.

5. Delete any TranslationMessages attached to those POTMsgSets.

6. Delete those POTMsgSets.

7. Delete all POFiles that refer to the template. Any references in POFileTranslator should have gone away when we deleted the TranslationMessages.

8. Delete the POTemplate.

Merge POTMsgSets

At the end of this phase, TranslationMessages will still be mostly diverged, but they'll be sharing POTMsgSets.

This phase requires at least a freeze on imports.

It's best to go through this separately per Ubuntu release, and maybe once for everything else. We must stop imports for whatever product or distroseries we're merging, which we can do individually for each Ubuntu series.

• Define equivalence class of POTemplate as belonging to POTemplates of the same name (not translation domain?) within either the same Product or the same DistroSeries.

• Define equivalence class of POTMsgSets as being attached (by TranslationTemplateItem) to POTemplates of the same equivalence class, and having the same (msgid_singular, COALESCE(msgid_plural, -1), COALESCE(context, )).

• Define the representative POTMsgSet in an equivalence class as the one in the series that has translation focus, if any; or failing that, the one with the highest id.

Steps:

1. For each equivalence class of POTMsgSets, merge all TranslationTemplateItems into those of the representative POTMsgSet.

2. For each converged current or imported TranslationMessage:

   • - if the representative POTMsgSet already has another converged current/imported TranslationMessage, clear the current/imported flag.

3. For each TranslationMessage:

   • - replace potmsgset with its representative POTMsgSet.

4. From each POTMsgSet equivalence class:

   • - delete all members but the representative one.

     - TODO: What if new TranslationMessages for these have appeared in the meantime?

Merge TranslationMessages