SchemaCache is not updated across multiple Plone instances

[avoinea]

How to reproduce:

1. Start a ZEO cluster with 2 Plone ZEO clients
2. Add Plone Site
3. Go to first Plone instance > Site Setup > Dexterity Content-Types > Page
4. Add new fieldset and new text field and press "Done"
5. Go to the second Plone instance > Site Setup > Dexterity Content-Types > Page
6. Notice the missing custom fieldset / field

Plone version: 5.2.2

See also:

• SchemaCache is not updated across multiple Plone instances plone.schemaeditor#81
• https://community.plone.org/t/dynamic-schema-is-not-synced-across-zeo-clients/12923

[jensens]

@avoinea you wrote in plone/plone.schemaeditor#81

My proposal is to also check fti._p_time, somehow

But at
https://github.com/plone/plone.dexterity/blob/master/plone/dexterity/schema.py#L107
the stored mtime from the cache is checked already against the _p_mtime from the FTI. So I dont think that's the problem.

Moreover I suspect the fti_cache on the request itself is the problem and needs invalidation. I guess it contains the old _p_mtime for some reason. Maybe I am wrong, Just a rough shoot.

[avoinea]

@jensens See https://github.com/plone/plone.dexterity/pull/137/files

The problem is like this:

1. The first time you access schema for Document a new class called Plone_0_Document is generated and persisted as plone.dexterity.schema.generated.Plone_0_Document
2. The next time, it is directly imported from plone.dexterity.schema.generated.Plone_0_Document
3. When you add a new field, it is directly added to plone.dexterity.schema.generated.Plone_0_Document and then serialized to fti model_source XML.

This is OK as a workflow when you have only one Plone instance. When you have multiple, each Plone instance will have it's own version of Plone_0_Document depending on when it was first accessed, and will read and write there.

What I do with this PR, is to also add fti._p_mtime as a variant of generated class name, thus we'll have: Plone_delimiter_ModificationTime_delimiter_PortalType_delimiter_schema

This will ensure that you load the latest version of the schema on each Plone instance as the _p_mtime is persisted to ZODB.

_PS. I couldn't add the timestamp at the end as the _schema is optional, and the code will misinterpret our timestamp as schema