Planet Plone - Where Developers And Integrators Write

Plone Conference 2022 - Namur

Posted by kitconcept GmbH on October 17, 2022 03:00 PM

Group Photo Plone Conference 2022 in Namur

The 2022 editon of the anual Plone conference happend from October 10th to 16th in Namur, Belgium.

The kitconcept team was present with nine developers. Our team members gave three trainings, two keynotes, and six talks.


Two days filled with trainings. Free for all conference attendees. This offer is unique in the Plone community and kitconcept team members were the backbone of the trainings about how to use Plone 6. From deployment to development to deep insides into how Volto and Plone 6 works.

Alok Kumar, Jakob Kahl: Volto and React

Alok Kumar and Jakob Kahl did a two day training to help developers get started with Volto and React:

Check out their trainings online if you want to catch up:

Érico Andrei, Jens Klein: Installing Plone

Our colleague Érico Andrei gave a training about installing Plone with Jens Klein on day one about how to install Plone:

Victor Fernandez de Alba, Tiberiu Ichim: Effective Volto

Victor Fernandez de Alba is kitconcept CTO and the Volto Release Manager. Tiberiu Ichim is a Volto team member and one of the key contributors to Volto. They gave key insights into how to work effectively with Volto. If you have experience with Volto and you want to become a real pro, this is the training you should go to.

Day One

On day one, kitconcept team members presented three talks, including the main keynote of the day.

Keynote Érico Andrei

Plone Foundation president, and our teammate, Érico Andrei kicked off the first day of the conference with a keynote about the Plone community.

Case Study by Timo Stollenwerk

kitconcept CEO Timo Stollenwerk presented a case study about how kitconcept relaunched hundreds of websites with the Plone 6 stack.

Plone at Scale: How Plone Powers Hundreds of Websites at one of the Largest Research Institutions in Europe

Alok Kumar

Alok Kumar presented “A Deep Dive Into Internals Of Volto” where he explained the different configuration options in Volto.

Day Two

Plone 6 beyond 2022

Volto Release Manager Victor Fernandez de Alba presented the roadmap for Plone 6 and Volto beyond 2022.

David Glick: The past, present, and future of how we test Plone

Érico Andrei: Brazil still loves Plone

30 Million visitors on a single day. 670k content objects. If you are running a Plone site at scale you definitely want Érico Andrei on your team. He helped the Electoral Justice department in Brazil to run and scale Plone for the upcoming elections.

Rob Gietema: Nick: A Nearly Headless CMS

Rob Gietema started plone-react together with Roel Bruggink at the Beethoven Sprint 2017 in Bonn at the kitconcept office. This first became Volto and later Plone 6.

For Rob, this isn’t enough. Check out his latest “pet project” Nick CMS. A NodeJS-based CMS headless CMS backend that works flawlessly with Volto.

Day 3

Timo Stollenwerk, Victor Fernandez de Alba: State of Plone

Plone Release Managers Maurits van Rees, Eric Steele, Victor Fernández de Alba, and Timo Stollenwerk started day three of the Plone Conference with the third keynote about “The State of Plone”:


The kitconcept team continues to drive innovation in the Plone community. Volto is the default frontend for Plone 6 and dominates the topics during the conference. We are happy to be part of such an amazing community.

Volto recipe for footer actions managed as site content

Posted by PloneExpanse on July 18, 2022 02:10 PM
Managing the Footer as content is one of the common tasks on a Plone / Volto website. One typical approach is to designate some root folder, let’s say footer-links as a container for Link instances, and use those links as shortcuts to dedicated pages. So, a footer component may look like this: import React from 'react'; import { getContent } from '@plone/volto/actions'; import { useSelector } from 'react-redux'; import {UniversalLink} from '@plone/volto/components'; const Footer = () => { const footerLinks = useSelector((state) => state.

Indexes in catalog.xml considered harmful

Posted by Maurits van Rees on March 16, 2022 08:41 PM
Do not add indexes in catalog.xml. Do that in a separate import or upgrade step. Read on for how to do that; I will throw in some general GenericSetup best practices along the way.

Custom Volto configuration to fix Babel problems with react-leaflet

Posted by PloneExpanse on February 06, 2022 04:05 PM
I’ve started working on a new Leaflet-powered Volto map block and the first thing that happened while loading react-leaftlet was an error reported by the browser: Module parse failed: Unexpected token (10:41) in @react-leaflet/core/esm/path.js ... const options = props.pathOptions ?? {}; ... The problem is that is, for some reasons, the transpiled JS bundle includes code using the nulish coalescing operator This is already a problem reported in react-leaflet and it happens because the distributed transpiled library includes that code.

On The Road to Plone 6 - Volto 14 Released

Posted by kitconcept GmbH on December 22, 2021 09:24 PM

Volto continues to innovate at a fast pace towards Plone 6. Today we released another major milestone on our road to Plone 6: Volto 14.

Volto 14 was in the making since September 2021 and it is in active use in various projects at Eau de Web, Red Turtle, Rohberg, kitconcept, and others.

Volto 14 comes with a set of new exiting features: a new search block that supports faceted search, locking support, a new seamless mode that makes deploying Volto easier, a new mobile navigation and support for Node 16.

Faceted Search Block

The new search block allows editor to create sophisticated faceted searches through the web without writing a single line of code.

Editors can define criteria for the content that is listed, like in the existing listing block in Volto.

Then editors can then choose arbitrary facets that are displayed to the users to choose from to narrow down the search.


Locking in a Content Management System is a mechanism to prevent users from accidentially overriding each others changes.

When a user edits a content object in Plone, the object is locked until the user hits the save or cancel button. If a second user tries to edit the object at the same time, she will see a message that this object is locked.

volto14 locking Content object in Volto 14 that is locked by another user

Locking requires at least plone.restapi 8.9.0 or plone.restapi 7.4.0 to be installed.

Seamless Mode

The new “seamless mode” allows zero configuration deployment by avoiding hardcoded environment variables in builds involved, and establishing good sensible defaults when setting up deployments (and also in development). So the developer/devOps doesn’t have to overthink their setups.

These are its main features:

  • Runtime environment variables
  • Unified traversal ++api++
  • Use Host header to auto-configure the API_PATH

and these immediate benefits:

  • Avoid having to expose and publish the classic UI if you don’t really need it
  • If possible, avoid having to rewrite all API responses, since it returns paths that do not correspond to the original object handled and “seen” from Volto, so you have to adjust them (via a code helper) in a lot of call responses.
  • Simplify Docker builds, making all the configuration via the runtime environment variables

Seamless Mode requires at least 2.0.0a1 to be installed.

New Mobile Navigation

We polished the mobile navigation for Volto 14 to improve the user experience on mobile.

New mobile navigation in action on the Plone Conference 2021 website

Node 16

Volto 16 will support Node 16 in addition to Node 14 and Node 12. Node 16 will receive security updates until April 2024.

node 16 Node 16 release schedule from

Plone 6

Volto 14 is an important step towards Plone 6. Volto 15 will switch the default editor from DraftJS to Slate editor and it is planned to be ready in Q1/Q2 2022. This is the last big step for Volto before Plone 6 can be released.

David Ichim: What's new in Plone 6 frontend for developers

Posted by Maurits van Rees on November 08, 2021 11:18 AM
Talk by David Ichim at the online Plone Conference 2021.

Tiberiu Ichim: Volto Pluggables

Posted by Maurits van Rees on November 08, 2021 09:55 AM
Talk by Tiberiu Ichim at the online Plone Conference 2021.

Stefan Antonelli and Peter Holzer: Theming Plone 6 Classic UI

Posted by Maurits van Rees on November 04, 2021 09:48 PM
Talk by Stefan Antonelli and Peter Holzer at the online Plone Conference 2021.

Steering Circle

Posted by Maurits van Rees on October 31, 2021 02:39 PM
Meeting of Plone's Steering Circle at the online Plone Conference 2021.

Annette Lewis and Will Gwin: From Zope to Plone: Thinking User-First During Migration

Posted by Maurits van Rees on October 28, 2021 02:39 PM
Talk by Annette Lewis and Will Gwin at the online Plone Conference 2021.

Lightning talks Wednesday

Posted by Maurits van Rees on October 27, 2021 08:35 PM
Lightning talks on Wednesday at the online Plone Conference 2021.

Thomas Schorr: Pyruvate WSGI Server Status Update

Posted by Maurits van Rees on October 27, 2021 07:23 PM
Talk by Thomas Schorr at the online Plone Conference 2021.

Tiberiu Ichim: Volto slots, portlets on steroids

Posted by Maurits van Rees on October 27, 2021 03:55 PM
Talk by Tiberiu Ichim at the online Plone Conference 2021.

Philip Bauer: A new hope for migrations and upgrades

Posted by Maurits van Rees on October 27, 2021 02:33 PM
Talk by Philip Bauer at the online Plone Conference 2021.

Lightning talks Tuesday

Posted by Maurits van Rees on October 26, 2021 06:05 PM
Lightning talks on Tuesday at the online Plone Conference 2021.

Jens Klein: Forging a New Installer

Posted by Maurits van Rees on October 26, 2021 03:06 PM
Talk by Jens Klein at the online Plone Conference 2021.

Philip Bauer: Why relations are awesome

Posted by Maurits van Rees on October 26, 2021 02:28 PM
Talk by Philip Bauer at the online Plone Conference 2021.

Timo Stollenwerk: Plone 6 - Power and Control

Posted by Maurits van Rees on October 26, 2021 01:44 PM
Keynote talk by Timo Stollenwerk at the online Plone Conference 2021.

Maik Derstappen: Efficient Backend development for Plone

Posted by Maurits van Rees on October 25, 2021 07:24 PM
Talk by Maik Derstappen at the online Plone Conference 2021.

Chrissy Wainwright: State of the Plone Community

Posted by Maurits van Rees on October 25, 2021 01:25 PM
Keynote talk by Chrissy Wainwright at the online Plone Conference 2021.

On The Road to Plone 6 - Plone REST API 7 and Volto 12 Released!

Posted by kitconcept GmbH on April 12, 2021 09:24 AM

Two weeks ago we cut two important releases on the road to Plone 6. Plone REST API 7 introduces a new link integrity feature for blocks-based pages. Volto 12 improves the add-on ecosystem by introducing a new configuration registry to avoid circular dependencies.

stephen leonardi 5CH1TNfcZoo unsplash Photo by Stephen Leonardi on Unsplash

Plone REST API 7

Linking pages is one of the core idea of the world wide web. Keeping links within a website intact is therefore one of the core features that any Content Management System needs to provide.

One of the core features of Plone has always been that editors can copy and move single pages as well as large content trees without breaking internal links to other parts of the site. This is accomplished by using unigue IDs (UUIDs) instead of relative or absolute paths when adding a link to another page. Plone uses “portal transforms” internally to rewrite those links in RichText fields on save operations.

Plone 6 (aka Volto) introduces blocks-based page layouts, that store a JSON structure internally instead of HTML. This more structured way of storing page content and layout allows more complex page layouts. Though, because of this change, the existing portal transforms mechanism that rewrites links to UUIDs did not work any longer.

volto blocks edit mode Blocks-based Volto page in edit mode (with kitconcept-blocks-grid)

Werkbank, a Plone agency from Bochum, Germany, stepped up to sponsor the development of link integrity in 2020, since they needed that for a client project.

I started to draft a possible solution and wrote a first prototype. Thomas Buchenberger from 4teamwork picked up that work at the Plone Conference sprint in Ferrara, Italy.

Andrea Cecchi from RedTurtle joined our efforts and refactored the resolveUID algorithm into a blocks transformer, that we started to use for other use cases and that made the resolveUID transformer more generic and flexible.

After that, we cut a first plone.restapi 7 alpha release and entered a longer period of quality assurance and testing.

Two weeks ago, after we tested the new feature in multiple projects at kitconcept, I cut a final release of Plone REST API 7.

After the first alpha release, the ResolveUID transformation was added to links and images. In addition plone.restapi 7 comes with a new blocks serialization mechanism and an important fix that makes sure files are opened directly by Plone for anonymous users.

We also added a “smart fields” concept that allows integrators to mark a blocks field as searchableText field.

A new @contextnavigation endpoint was added that allows for local navigations. We enhanced the navigation endpoint to expose an optional navigation title (“nav_title”) field.

Since the final 7 release, we cut six more releases and REST API 7 was included in Plone 5.2.4 release.

Volto 12

gaelle marcel vrkSVpOwchk unsplash Photo by Gaelle Marcel on Unsplash

Tiberiu and Victor worked on a new Volto configuration registry which is the new central point to store and retrieve Volto configurations. The configuration registry is a singleton that ensures a setting only exists once. With more an more Volto add-ons that started to depend on each other, we started to run into circular dependencies issues that we can avoid now with the new configuration registry.

You can find more details about it in the Volto docs and in the Volto 12 upgrade guide.

Plone 6

Plone REST API 7 and Volto 12 were two very important releases on our road to Plone 6.

We plan to cut another Plone REST API 8 branch and release for Plone 6, which will support Python 3 only.

Volto will continue to move at very high pace towards Plone 6. We started to organize a series of Plone 6 “Micro-Sprints” to push things further.

Check out the Volto Roadmap on github for more details.

Lightning Talks Wednesday

Posted by Maurits van Rees on December 09, 2020 06:21 PM
Lightning Talks on Wednesday at the Plone Conference 2020

Lightning talks Monday

Posted by Maurits van Rees on December 09, 2020 10:19 AM
Lightning talks on Monday at Plone Conference 2020

Plone Connection Podcast: Episode 01 - Philip Bauer

Posted by on November 19, 2020 04:56 PM

The Plone Connection Podcast is a monthly podcast produced by Six Feet Up. Every month, Six Feet Up's Director of Engineering T. Kim Nguyen sits down with a different member of the Plone Community and asks them about their work with or on the Plone CMS.

Many thank to my good friend Kim for doing this!

Your first Plone 6 Project

Posted by on November 18, 2020 01:25 PM

I've had the opportunity to give this talk at the most excellent Python Web Conference.

ZODB Database debugging

Posted by on August 24, 2020 11:00 AM

The problem

The ZODB contains python objects serializes as pickles. When a object is loaded/used a pickle is deserialized ("unpickled") into a python object.

A ZODB can contain objects that cannot be loaded. Reasons for that may be:

  • Code could not be loaded that is required to unpickle the object (e.g. removed packages, modules or classes)
  • Objects are referenced but missing from the database (e.g. a blob is missing)
  • The objects contains invalid entries (e.g. a reference to a oid that uses a no longer supported format)

The most frequent issues are caused by:

  • Improperly uninstalled or removed packages (e.g. Archetypes, ATContentTypes, CMFDefault, PloneFormGen etc.)
  • Code has changed but not all objects that rely on that code as updated
  • Code was refactored and old imports are no longer working

You should not blame the migration to Python 3 for these issues! Many issues may already exists in their database before the migration but people usually do not run checks to find issues. After a migration to Python 3 most people check their database for the first time. This may be because the documentation on python3-migration recommends running the tool zodbverify.

Real problems may be revealed at that point, e.g when:

  • Packing the Database fails
  • Features fail

You can check you ZODB for problems using the package zodbverify. To solve each of the issues you need to be able to answer three questions:

  1. Which object is broken and what is the error?
  2. Where is the object and what uses it?
  3. How do I fix it?

In short these approaches to fixing exist:

  1. Ignore the errors
  2. Add zodbupgrade mappings
  3. Patch your python-path to work around the errors
  4. Replace broken objects with dummies
  5. Remove broken objects the hard way
  6. Find our what and where broken objects are and then fix or remove them safely

I will mostly focus on the last approach.

But before you spend a lot of time to investigate individual errors it would be a good idea to deal with the most frequent problems, especially IntIds and Relations (see the chapter "Frequent Culprits") below. In my experience these usually solved most issues.

Find out what is broken

Check your entire database

Use zodbverify to verify a ZODB by iterating and loading all records. zodbverify is available as a standalone script and as addon for plone.recipe.zope2instance. Use the newest version!

In the simplest form run it like this:

$ bin/zodbverify -f var/filestorage/Data.fs

It will return:

  • a list of types of errors
  • the number of occurences
  • all oids that raise that error on loading


zodbverify is only available for Plone 5.2 and later. For older Plone-Versions use the scripts and from the ZODB package:

$ ./bin/zopepy ./parts/packages/ZODB/scripts/ var/filestorage/Data.fs

$ ./bin/zopepy ./parts/packages/ZODB/scripts/ var/filestorage/Data.fs

The output of zodbverify might look like this abbreviated example from a medium-sized intranet (1GB Data.fs, 5GB blobstorage) that started with Plone 4 on Archetypes and was migrated to Plone 5.2 on Python 3 and Dexterity:

$ ./bin/zodbverify -f var/filestorage/Data.fs


INFO:zodbverify:Done! Scanned 163955 records.

Found 1886 records that could not be loaded.

Exceptions, how often they happened and which oids are affected:

ModuleNotFoundError: No module named 'Products.Archetypes': 1487

0x0e00eb 0x0e00ee 0x0e00ef 0x0e00f0 0x0e00f1 0x2b194b 0x2b194e 0x2b194f 0x2b1950 [...]

ModuleNotFoundError: No module named 'Products.PloneFormGen': 289

0x2b1940 0x2b1941 0x2b1942 0x2b1943 0x2b1944 0x2b1974 0x2b1975 0x2b1976 0x2b1977 [...]

AttributeError: module 'App.interfaces' has no attribute 'IPersistentExtra': 34

0x2c0a69 0x2c0a6b 0x2c0ab7 0x2c0ab9 0x2c555d [...] 0x35907f

ModuleNotFoundError: No module named 'Products.CMFDefault': 20

0x011e 0x011f 0x0120 0x0121 0x0122 0x0123 0x0124 0x0125 0x0126 0x0127 0x0128 0x0129 0x012a 0x012b 0x012c 0x012d 0x012e 0x012f 0x0130 0x0131

ModuleNotFoundError: No module named 'webdav.interfaces'; 'webdav' is not a package: 20

0x3b1cde 0x3b1ce0 0x3b1ce4 0x3b1ce6 0x3b1ce9 0x3b1ceb 0x3b1cee 0x3b1cf0 0x3b1cf4 0x3b1cf6 0x3b1cf9 0x3b1cfb 0x3b1cfe 0x3b1d00 0x3b1d04 0x3b1d06 0x3b1d09 0x3b1d0b 0x3b1d0e 0x3b1d10

ModuleNotFoundError: No module named 'webdav.EtagSupport'; 'webdav' is not a package: 16

0x2c0a68 0x2c0a6a 0x2c555c 0x2c555e 0x2c560b 0x2c560d 0x2c5663 0x2c5665 0x2c571b 0x2c571d 0x2c5774 0x2c5776 0x2c5833 0x2c5835 0x33272d 0x33272f

ModuleNotFoundError: No module named 'fourdigits': 8

0x28030f 0x280310 0x280311 0x280312 0x280313 0x280314 0x280315 0x280316

ModuleNotFoundError: No module named 'Products.ATContentTypes': 4

0x0e00e9 0x0e011a 0x0e01b3 0x0e0cb3

AttributeError: module '' has no attribute 'IEventSettings': 3

0x2a712b 0x2a712c 0x2a712d

ModuleNotFoundError: No module named 'Products.PloneLanguageTool': 1


ModuleNotFoundError: No module named 'Products.CMFPlone.MetadataTool': 1


ModuleNotFoundError: No module named 'Products.CMFPlone.DiscussionTool': 1


ModuleNotFoundError: No module named '': 1


ModuleNotFoundError: No module named 'Products.ResourceRegistries': 1


You can see all different types of errors that appear and which objects are causing them. Objects are referenced by their oid in the ZODB. See the Appendix on how to deal with oids.

You can see that among other issues there are still a lot of references to Archetypes and PloneFormGen (I omitted the complete lists) even though both are no longer used in the site.

Before the summary the log dumps a huge list of errors that contain the pickle and the error:


Could not process unknown record 0x376b77 (b'\x00\x00\x00\x00\x007kw'):

INFO:zodbverify:b'\x80\x03cProducts.PloneFormGen.content.thanksPage\nFormThanksPage\nq\x00.\x80\x03}q\x01(X\x0c\x00\x00\x00showinsearchq\x02\x88X\n\x00\x00\x00_signatureq\x03C\x10\xd9uH\xc0\x81\x14$\xf5W:C\x80x\x183\xc7q\x04X\r\x00\x00\x00creation_dateq\x05cDateTime.DateTime\nDateTime\nq\x06)\x81q\x07GA\xd6\xdf_\xba\xd56"\x89X\x05\x00\x00\x00GMT+2q\x08\x87q\tbX\r\x00\x00\x00marshall_hookq\nNX\n\x00\x00\x00showFieldsq\x0b]q\x0cX\x02\x00\x00\x00idq\rX\t\x00\x00\x00thank-youq\x0eX\x11\x00\x00\x00_at_creation_flagq\x0f\x88X\x11\x00\x00\x00modification_dateq\x10h\x06)\x81q\x11GA\xd6\xdf_\xba\xd7\x15r\x89h\x08\x87q\x12bX\x05\x00\x00\x00titleq\x13X\x05\x00\x00\x00Dankeq\x14X\x0f\x00\x00\x00demarshall_hookq\x15NX\x0e\x00\x00\x00includeEmptiesq\x16\x88X\x0e\x00\x00\x00thanksEpilogueq\x17C\x08\x00\x00\x00\x00\x007k\xaaq\x18cProducts.Archetypes.BaseUnit\nBaseUnit\nq\x19\x86q\x1aQX\x07\x00\x00\x00showAllq\x1b\x88X\x12\x00\x00\x00_EtagSupport__etagq\x1cX\r\x00\x00\x00ts34951147.36q\x1dX\x0b\x00\x00\x00portal_typeq\x1eX\x0e\x00\x00\x00FormThanksPageq\x1fX\x0b\x00\x00\x00searchwordsq C\x08\x00\x00\x00\x00\x007k\xabq!h\x19\x86q"QX\x07\x00\x00\x00_at_uidq#X \x00\x00\x00a2d15a36a521471daf2b7005ff9dbc62q$X\r\x00\x00\x00at_referencesq%C\x08\x00\x00\x00\x00\x007k\xacq&cOFS.Folder\nFolder\nq\'\x86q(QX\x0e\x00\x00\x00thanksPrologueq)C\x08\x00\x00\x00\x00\x007k\xadq*h\x19\x86q+QX\x0f\x00\x00\x00noSubmitMessageq,C\x08\x00\x00\x00\x00\x007k\xaeq-h\x19\x86q.QX\x03\x00\x00\x00_mdq/C\x08\x00\x00\x00\x00\x007k\xafq0cPersistence.mapping\nPersistentMapping\nq1\x86q2QX\x12\x00\x00\x00__ac_local_roles__q3}q4X\x16\x00\x00\x00xxx@xxx.deq5]q6X\x05\x00\x00\x00Ownerq7asu.'

INFO:zodbverify:Traceback (most recent call last):

  File "/Users/pbauer/workspace/dipf-intranet/src-mrd/zodbverify/src/zodbverify/", line 62, in verify_record

    class_info = unpickler.load()

  File "/Users/pbauer/.cache/buildout/eggs/ZODB-5.5.1-py3.8.egg/ZODB/", line 62, in find_class

    return super(Unpickler, self).find_class(modulename, name)

ModuleNotFoundError: No module named 'Products.PloneFormGen'

Inspecting a single object

In this case the object with the oid 0x376b77 seems to be a FormThanksPage from Products.PloneFormGen. But wait! You deleted all of these, so where in the site is it?

If the offending object is normal content the solution is mostly simple. You can call obj.getPhysicalPath() to find out where it is. But ore often than not editing and saving will fix the problem. In other cases you might need to copy the content to a new item and delete the broken object.

But usually it is not simply content but something else. Here are some examples:

  • A annotation on a object or the portal
  • A relationvalue in the relatopn-catalog
  • A item in the IntId catalog
  • A old revision of content in CMFEditions
  • A configuration-entry in portal_properties or in portal_registry

The hardest part is to find out what and where the broken object actually is before removing or fixing it.

The reason for that is that a entry in the ZODB does not know about it's parent. Acquisition finds parents with obj.aq_parent() but many items are not-Acquisition-aware. Only the parents that reference objects know about them.

A object x could be the attribute some_object on object y but you will not see that by inspecting x. Only y knows that x is y.some_object.

A way to work around this is used by the script on ZODB. It allows you to list all incoming and outgoing references to a certain object.

With this you will see that x is referenced by y. With this information you can then inspect the object y and hopefully see how x is set on y.

More often than not y is again not a object in the content-hierarchy but maybe a BTree of sorts, a pattern that is frequently used for effective storage of many items. Then you need to find out the parent of y to be able to fix x.

And so forth. It can a couple of steps until you end up in a item that can be identified, e.g. portal_properties or RelationCatalog and usually only exists once in a database.

To make the process of finding this path less tedious I extended zodbverify in with a feature that will show you all parents and their parents in a way that allows you to see where in the tree is it.

Before we look at the path of 0x376b77 we'll inspect the object.

Pass the oid and the debug-flag -D to zodbverify with ./bin/zodbverify -f var/filestorage/Data.fs -o 0x376b77 -D:

$ ./bin/zodbverify -f var/filestorage/Data.fs -o 0x376b77 -D

INFO:zodbverify:Inspecting 0x376b77:

<persistent broken Products.PloneFormGen.content.thanksPage.FormThanksPage instance b'\x00\x00\x00\x00\x007kw'>


Object as dict:

{'__Broken_newargs__': (), '__Broken_state__': {'showinsearch': True, '_signature': b'\xd9uH\xc0\x81\x14$\xf5W:C\x80x\x183\xc7', 'creation_date': DateTime('2018/08/22 17:19:7.331429 GMT+2'), 'marshall_hook': None, 'showFields': [], 'id': 'thank-you', '_at_creation_flag': True, 'modification_date': DateTime('2018/08/22 17:19:7.360684 GMT+2'), 'title': 'Danke', 'demarshall_hook': None, 'includeEmpties': True, 'thanksEpilogue': <persistent broken Products.Archetypes.BaseUnit.BaseUnit instance b'\x00\x00\x00\x00\x007k\xaa'>, 'showAll': True, '_EtagSupport__etag': 'ts34951147.36', 'portal_type': 'FormThanksPage', 'searchwords': <persistent broken Products.Archetypes.BaseUnit.BaseUnit instance b'\x00\x00\x00\x00\x007k\xab'>, '_at_uid': 'a2d15a36a521471daf2b7005ff9dbc62', 'at_references': <Folder at at_references>, 'thanksPrologue': <persistent broken Products.Archetypes.BaseUnit.BaseUnit instance b'\x00\x00\x00\x00\x007k\xad'>, 'noSubmitMessage': <persistent broken Products.Archetypes.BaseUnit.BaseUnit instance b'\x00\x00\x00\x00\x007k\xae'>, '_md': <Persistence.mapping.PersistentMapping object at 0x111617c80 oid 0x376baf in <Connection at 11094a550>>, '__ac_local_roles__': {'': ['Owner']}}}


The object is 'obj'

[2] > /Users/pbauer/workspace/dipf-intranet/src-mrd/zodbverify/src/zodbverify/

-> pickle, state = storage.load(oid)


Even before you use the provided pdb to inspect it you can see that it is of the class persistent broken, a way of the ZODB to give you access to objects even though their class can no longer be imported.

You can now inspect it:

(Pdb++) obj

<persistent broken Products.PloneFormGen.content.thanksPage.FormThanksPage instance b'\x00\x00\x00\x00\x007kw'>

(Pdb++) pp obj.__dict__

{'__Broken_newargs__': (),

 '__Broken_state__': {'_EtagSupport__etag': 'ts34951147.36',

                      '__ac_local_roles__': {'': ['Owner']},

                      '_at_creation_flag': True,

                      '_at_uid': 'a2d15a36a521471daf2b7005ff9dbc62',

                      '_md': <Persistence.mapping.PersistentMapping object at 0x111617c80 oid 0x376baf in <Connection at 11094a550>>,

                      '_signature': b'\xd9uH\xc0\x81\x14$\xf5W:C\x80x\x183\xc7',

                      'at_references': <Folder at at_references>,

                      'creation_date': DateTime('2018/08/22 17:19:7.331429 GMT+2'),

                      'demarshall_hook': None,

                      'id': 'thank-you',

                      'includeEmpties': True,

                      'marshall_hook': None,

                      'modification_date': DateTime('2018/08/22 17:19:7.360684 GMT+2'),

                      'noSubmitMessage': <persistent broken Products.Archetypes.BaseUnit.BaseUnit instance b'\x00\x00\x00\x00\x007k\xae'>,

                      'portal_type': 'FormThanksPage',

                      'searchwords': <persistent broken Products.Archetypes.BaseUnit.BaseUnit instance b'\x00\x00\x00\x00\x007k\xab'>,

                      'showAll': True,

                      'showFields': [],

                      'showinsearch': True,

                      'thanksEpilogue': <persistent broken Products.Archetypes.BaseUnit.BaseUnit instance b'\x00\x00\x00\x00\x007k\xaa'>,

                      'thanksPrologue': <persistent broken Products.Archetypes.BaseUnit.BaseUnit instance b'\x00\x00\x00\x00\x007k\xad'>,

                      'title': 'Danke'}}

If you now choose to continue (by pressing c) zodbverify it will try to disassemble the pickle. That is very useful for in-depth debugging but out of the scope of this documentation.

Inspect the path of references

Now you know it is broken but you still don't know where this ominous FormThanksPage actually is.

Continue to let zodbverify find the path to the object:

INFO:zodbverify:Building a reference-tree of ZODB...


INFO:zodbverify:Created a reference-dict for 163955 objects.


This oid is referenced by:

INFO:zodbverify:0x376ada BTrees.IOBTree.IOBucket at level 1

INFO:zodbverify:0x28018c BTrees.IOBTree.IOBTree at level 2

INFO:zodbverify:0x280184 five.intid.intid.IntIds at level 3

INFO:zodbverify:0x1e five.localsitemanager.registry.PersistentComponents at level 4

INFO:zodbverify:0x11 Products.CMFPlone.Portal.PloneSite at level 5

INFO:zodbverify:0x01 OFS.Application.Application at level 6

INFO:zodbverify: 8< --------------- >8 Stop at root objects

INFO:zodbverify:0x02f6 persistent.mapping.PersistentMapping at level 7

INFO:zodbverify: 8< --------------- >8 Stop at root objects

INFO:zodbverify:0x02f7 zope.component.persistentregistry.PersistentAdapterRegistry at level 8

INFO:zodbverify: 8< --------------- >8 Stop at root objects

INFO:zodbverify:0x02f5 at level 6

INFO:zodbverify:0x02fa zope.ramcache.ram.RAMCache at level 7

INFO:zodbverify:0x02fd at level 8

INFO:zodbverify:0x338f13 at level 9

INFO:zodbverify:0x0303 BTrees.OOBTree.OOBTree at level 10

INFO:zodbverify:0x346961 at level 10

INFO:zodbverify: 8< --------------- >8 Stop after level 10!

INFO:zodbverify: 8< --------------- >8 Stop after level 10!

INFO:zodbverify:0x02fe at level 9

INFO:zodbverify:0x034d plone.keyring.keyring.Keyring at level 10

INFO:zodbverify: 8< --------------- >8 Stop after level 10!

INFO:zodbverify: 8< --------------- >8 Stop after level 10!

INFO:zodbverify: 8< --------------- >8 Stop after level 10!

INFO:zodbverify: 8< --------------- >8 Stop after level 10!

INFO:zodbverify:0x376864 BTrees.IOBTree.IOBucket at level 3

INFO:zodbverify:0x31049f BTrees.IOBTree.IOBucket at level 4

INFO:zodbverify:0x325823 BTrees.IOBTree.IOBucket at level 5

INFO:zodbverify:0x3984c8 BTrees.IOBTree.IOBucket at level 6

INFO:zodbverify:0x2cce9a BTrees.IOBTree.IOBucket at level 7

INFO:zodbverify:0x2c6669 BTrees.IOBTree.IOBucket at level 8

INFO:zodbverify:0x2c62b4 BTrees.IOBTree.IOBucket at level 9

INFO:zodbverify:0x2c44c1 BTrees.IOBTree.IOBucket at level 10

INFO:zodbverify: 8< --------------- >8 Stop after level 10!

INFO:zodbverify:0x377536 BTrees.OIBTree.OIBucket at level 2

INFO:zodbverify:0x376b14 BTrees.OIBTree.OIBucket at level 3

INFO:zodbverify:0x376916 BTrees.OIBTree.OIBucket at level 4

INFO:zodbverify:0x376202 BTrees.OIBTree.OIBucket at level 5

INFO:zodbverify:0x373fa7 BTrees.OIBTree.OIBucket at level 6

INFO:zodbverify:0x37363a BTrees.OIBTree.OIBucket at level 7

INFO:zodbverify:0x372f26 BTrees.OIBTree.OIBucket at level 8

INFO:zodbverify:0x372cc8 BTrees.OIBTree.OIBucket at level 9

INFO:zodbverify:0x36eb86 BTrees.OIBTree.OIBucket at level 10

INFO:zodbverify: 8< --------------- >8 Stop after level 10!

INFO:zodbverify: 8< --------------- >8 Stop after level 10!

INFO:zodbverify: 8< --------------- >8 Stop after level 10!

INFO:zodbverify:0x407185 BTrees.OIBTree.OIBTree at level 10

INFO:zodbverify: 8< --------------- >8 Stop after level 10!

You can see from the logged messages that the FormThanksPage is in a IOBucket which again is in a IOBTree which is in a object of the class five.intid.intid.IntIds which is part if the component-registry in the Plone site.

This means there is a reference to a broken object in the IntId tool. How to solve all these is covered below in the chapter "Frequent Culprits".

Decide how and if to fix it

In this case the solution is clear (remove refs to broken objects from the intid tool). But that is only one approach.

Often the solution is not presented like this (the solution to intid was not obvious to me until I spent considerable time to investigate).

The following six options to deal with these problems exists. Spoiler: Option 6 is the best approach in most cases but the other also have valid use-cases.

Option 1: Ignoring the errors

I do that a lot. Especially old databases that were migrated all the may from Plone 2 or 3 up to the current version have issues. If these issues never appear during operation and if clients have no budget or interest in fixing them you can leave them be. If they do not hurt you (e.g. you cannot pack your database or features actually fail) you can choose to ignore them.

At some point later they might appear and it may be a better time to fix them. I spent many hours fixing issues that will never show during operation.

Option 2: Migrating/Fixing a DB with zodbupdate

Use that when a module or class has moved or was renamed.


You can change objects in DB according to rules:

  • When a import has moved use a rename mapping
  • To specify if a obj needs to be decoded decode mapping

Examples from Zope/src/OFS/

zodbupdate_decode_dict = {

    'OFS.Image File data': 'binary',

    'OFS.Image Image data': 'binary',

    'OFS.Application Application title': 'utf-8',

    'OFS.DTMLDocument DTMLDocument title': 'utf-8',

    'OFS.DTMLMethod DTMLMethod title': 'utf-8',

    'OFS.DTMLMethod DTMLMethod raw': 'utf-8',

    'OFS.Folder Folder title': 'utf-8',

    'OFS.Image File title': 'utf-8',

    'OFS.Image Image title': 'utf-8',

    'OFS.Image Pdata title': 'utf-8',

    'OFS.Image Pdata data': 'binary',

    'OFS.OrderedFolder OrderedFolder title': 'utf-8',

    'OFS.userfolder UserFolder title': 'utf-8',


zodbupdate_rename_dict = {

    'webdav.LockItem LockItem': 'OFS.LockItem LockItem',


You can specify your own mappings in your own packages. These mappings need to be registered in so zodbupdate will pick them up.

Rename mapping example:

Decode mapping example:

Option 3: Work around with a patch

You can inject a module to work around missing or moved classes or modules.

The reason to want do this is usually because then you can safely delete items after that. They don't hurt your performance.

Examples in

# -*- coding: utf-8 -*-

from OFS.SimpleItem import SimpleItem

from import alias_module

from import bbb

from zope.interface import Interface

class IBBB(Interface):


class BBB(object):


SlideshowDescriptor = SimpleItem

# Interfaces


    from collective.z3cform.widgets.interfaces import ILayer

except ImportError:

    alias_module('collective.z3cform.widgets.interfaces.ILayer', IDummy)


    from App.interfaces import IPersistentExtra

except ImportError:

    alias_module('App.interfaces.IPersistentExtra', IDummy)


    from webdav.interfaces import IDAVResource

except ImportError:

    alias_module('webdav.interfaces.IDAVResource', IDummy)

# SimpleItem


    from collective.easyslideshow.descriptors import SlideshowDescriptor

except ImportError:

    alias_module('collective.easyslideshow.descriptors.SlideshowDescriptor', SlideshowDescriptor)

# object


    from collective.solr import interfaces

except ImportError:

    alias_module('collective.solr.indexer.SolrIndexProcessor', BBB)


    from Products.CMFPlone import UndoTool

except ImportError:

    sys.modules['Products.CMFPlone.UndoTool'] = bbb


Plone has plenty of these (see

Option 4: Replace broken objects with a dummy

If a objects is missing (i.e. you get a POSKeyError) or broken beyond repair you can choose to replace it with a dummy.

from persistent import Persistent

from ZODB.utils import p64

import transaction

app = self.context.__parent__

broken_oids = [0x2c0ab6, 0x2c0ab8]

for oid in broken_oids:

    dummy = Persistent()

    dummy._p_oid = p64(oid)

    dummy._p_jar = app._p_jar


    app._p_jar._added[dummy._p_oid] = dummy


You shoud be aware that the missing or broken object will be gone forever after you didi this. So before you choose to go down this path you should try to find out what the object in question actually was.

Option 5: Remove broken objects from db

from persistent import Persistent

from ZODB.utils import p64

import transaction

app = self.context.__parent__

broken_oids = [0x2c0ab6, 0x2c0ab8]

for oid in broken_oids:

    root = connection.root()

    del app._p_jar[p64(oid)]


I'm not sure if that is a acceptable approach under any circumstance since this will remove the pickle but not all references to the object. It will probably lead to PosKeyErrors.

Option 6: Manual fixing

This is how you should deal with most problems.

The way to go

  1. Use zodbverify to get all broken objects
  2. Pick one error-type at a time
  3. Use zodbverify with -o <OID> -D to inspect one object and find out where that object is referenced
  4. If you use follow referenced by until you find where in the tree the object lives. zodbverify will try to do it for you.
  5. Remove or fix the object (using a upgrade-step, pdb or a rename mapping)

Find out which items are broken

The newest version of zodbverify has a feature to that does the same task we discussed in Example 1 for you. Until it is merged and released you need to use the branch show_references from the pull-request

When inspecting a individual oid zodbverify builds a dict of all references for reverse-lookup. Then it recursively follow the trail of references to referencing items up to the root. To prevent irrelevant and recursive entries it aborts after level 600 and at some root-objects because these usually references a lot and would clutter the result with irrelevant information.

The output should give you a pretty good idea where in the object-tree a item is actually located, how to access and fix it.

If 0x3b1d06 is the broken oid inspect it with zodbverify:

$ ./bin/instance zodbverify -o 0x3b1d06 -D

2020-08-24 12:19:32,441 INFO    [Zope:45][MainThread] Ready to handle requests

2020-08-24 12:19:32,442 INFO    [zodbverify:222][MainThread]

The object is 'obj'

The Zope instance is 'app'

[4] > /Users/pbauer/workspace/dipf-intranet/src-mrd/zodbverify/src/zodbverify/

-> pickle, state = storage.load(oid)

(Pdb++) obj

<BTrees.OIBTree.OITreeSet object at 0x110b97ac0 oid 0x3b1d06 in <Connection at 10c524040>>

(Pdb++) pp [i for i in obj]

[<InterfaceClass OFS.EtagSupport.EtagBaseInterface>,


 <class 'webdav.interfaces.IDAVResource'>,

 <InterfaceClass plone.dexterity.interfaces.IDexterityContent>,



 <SchemaClass plone.supermodel.model.Schema>]

The problem now is that obj has no __parent__ so you have no way of knowing what you're actually dealing with.

When you press c for continue zodbverify will proceed and load the pickle:

(Pdb++) c

2020-08-24 12:20:50,784 INFO    [zodbverify:68][MainThread]

Could not process <class 'BTrees.OIBTree.OITreeSet'> record 0x3b1d06 (b'\x00\x00\x00\x00\x00;\x1d\x06'):

2020-08-24 12:20:50,784 INFO    [zodbverify:69][MainThread] b'\x80\x03cBTrees.OIBTree\nOITreeSet\nq\x00.\x80\x03(cOFS.EtagSupport\nEtagBaseInterface\nq\x01cAcquisition.interfaces\nIAcquirer\nq\\nIAllowDiscussion\nq\x03czope.annotation.interfaces\nIAnnotatable\nq\x04czope.annotation.interfaces\nIAttributeAnnotatable\nq\x05cplone.uuid.interfaces\nIAttributeUUID\nq\x06cProducts.CMFDynamicViewFTI.interfaces\nIBrowserDefault\nq\x07cProducts.CMFCore.interfaces\nICatalogAware\nq\x08cProducts.CMFCore.interfaces\nICatalogableDublinCore\nq\tczope.location.interfaces\nIContained\nq\ncProducts.CMFCore.interfaces\nIContentish\nq\x0bcOFS.interfaces\nICopySource\nq\x0ccwebdav.interfaces\nIDAVResource\nq\rcplone.dexterity.interfaces\nIDexterityContent\nq\\nIDexterityHasRelations\nq\x0fcplone.dexterity.interfaces\nIDexterityItem\nq\\nIDexterityIterateAware\nq\x11cplone.dexterity.interfaces\nIDexteritySchema\nq\\nIDocument\nq\x13cProducts.CMFCore.interfaces\nIDublinCore\nq\x14cProducts.CMFCore.interfaces\nIDynamicType\nq\\nIExcludeFromNavigation\nq\x16cz3c.relationfield.interfaces\nIHasIncomingRelations\nq\x17cz3c.relationfield.interfaces\nIHasOutgoingRelations\nq\x18cz3c.relationfield.interfaces\nIHasRelations\nq\x19cplone.namedfile.interfaces\nIImageScaleTraversable\nq\x1acOFS.interfaces\nIItem\nq\\nIIterateAware\nq\x1ccplone.portlets.interfaces\nILocalPortletAssignable\nq\x1dczope.location.interfaces\nILocation\nq\x1ecOFS.interfaces\nIManageable\nq\x1fcProducts.CMFCore.interfaces\nIMinimalDublinCore\nq cProducts.CMFCore.interfaces\nIMutableDublinCore\nq!cProducts.CMFCore.interfaces\nIMutableMinimalDublinCore\nq"\nINameFromTitle\nq#cApp.interfaces\nINavigation\nq$cProducts.CMFCore.interfaces\nIOpaqueItemManager\nq%cAccessControl.interfaces\nIOwned\nq&cAccessControl.interfaces\nIPermissionMappingSupport\nq\'cpersistent.interfaces\nIPersistent\nq(cOFS.interfaces\nIPropertyManager\nq)\nIRelatedItems\nq*cAccessControl.interfaces\nIRoleManager\nq+cplone.contentrules.engine.interfaces\nIRuleAssignable\nq,cProducts.CMFDynamicViewFTI.interfaces\nISelectableBrowserDefault\nq-cOFS.interfaces\nISimpleItem\\nITableOfContents\nq/cOFS.interfaces\nITraversable\nq0cplone.uuid.interfaces\nIUUIDAware\nq1cProducts.CMFEditions.interfaces\nIVersioned\\nIVersioningSupport\nq3cProducts.CMFCore.interfaces\nIWorkflowAware\nq4cOFS.interfaces\nIWriteLock\nq5cOFS.interfaces\nIZopeObject\nq6czope.interface\nInterface\nq7cplone.dexterity.schema.generated\nPlone_0_Document\nq8cplone.supermodel.model\nSchema\nq9tq:\x85q;\x85q<\x85q=.'

2020-08-24 12:20:50,786 INFO    [zodbverify:70][MainThread] Traceback (most recent call last):

  File "/Users/pbauer/workspace/dipf-intranet/src-mrd/zodbverify/src/zodbverify/", line 64, in verify_record


  File "/Users/pbauer/.cache/buildout/eggs/ZODB-5.5.1-py3.8.egg/ZODB/", line 62, in find_class

    return super(Unpickler, self).find_class(modulename, name)

ModuleNotFoundError: No module named 'webdav.interfaces'; 'webdav' is not a package

    0: \x80 PROTO      3

    2: (    MARK

    3: c        GLOBAL     'OFS.EtagSupport EtagBaseInterface'

   38: q        BINPUT     1

   40: c        GLOBAL     'Acquisition.interfaces IAcquirer'

   74: q        BINPUT     2

   76: c        GLOBAL     ' IAllowDiscussion'

  135: q        BINPUT     3

  137: c        GLOBAL     'zope.annotation.interfaces IAnnotatable'

  178: q        BINPUT     4

  180: c        GLOBAL     'zope.annotation.interfaces IAttributeAnnotatable'

  230: q        BINPUT     5

  232: c        GLOBAL     'plone.uuid.interfaces IAttributeUUID'

  270: q        BINPUT     6

  272: c        GLOBAL     'Products.CMFDynamicViewFTI.interfaces IBrowserDefault'

  327: q        BINPUT     7

  329: c        GLOBAL     'Products.CMFCore.interfaces ICatalogAware'

  372: q        BINPUT     8

  374: c        GLOBAL     'Products.CMFCore.interfaces ICatalogableDublinCore'

  426: q        BINPUT     9

  428: c        GLOBAL     'zope.location.interfaces IContained'

  465: q        BINPUT     10

  467: c        GLOBAL     'Products.CMFCore.interfaces IContentish'

  508: q        BINPUT     11

  510: c        GLOBAL     'OFS.interfaces ICopySource'

  538: q        BINPUT     12

  540: c        GLOBAL     'webdav.interfaces IDAVResource'

  572: q        BINPUT     13

  574: c        GLOBAL     'plone.dexterity.interfaces IDexterityContent'

  620: q        BINPUT     14

  622: c        GLOBAL     ' IDexterityHasRelations'

  681: q        BINPUT     15

  683: c        GLOBAL     'plone.dexterity.interfaces IDexterityItem'

  726: q        BINPUT     16

  728: c        GLOBAL     ' IDexterityIterateAware'

  791: q        BINPUT     17

  793: c        GLOBAL     'plone.dexterity.interfaces IDexteritySchema'

  838: q        BINPUT     18

  840: c        GLOBAL     ' IDocument'

  885: q        BINPUT     19

  887: c        GLOBAL     'Products.CMFCore.interfaces IDublinCore'

  928: q        BINPUT     20

  930: c        GLOBAL     'Products.CMFCore.interfaces IDynamicType'

  972: q        BINPUT     21

  974: c        GLOBAL     ' IExcludeFromNavigation'

 1040: q        BINPUT     22

 1042: c        GLOBAL     'z3c.relationfield.interfaces IHasIncomingRelations'

 1094: q        BINPUT     23

 1096: c        GLOBAL     'z3c.relationfield.interfaces IHasOutgoingRelations'

 1148: q        BINPUT     24

 1150: c        GLOBAL     'z3c.relationfield.interfaces IHasRelations'

 1194: q        BINPUT     25

 1196: c        GLOBAL     'plone.namedfile.interfaces IImageScaleTraversable'

 1247: q        BINPUT     26

 1249: c        GLOBAL     'OFS.interfaces IItem'

 1271: q        BINPUT     27

 1273: c        GLOBAL     ' IIterateAware'

 1317: q        BINPUT     28

 1319: c        GLOBAL     'plone.portlets.interfaces ILocalPortletAssignable'

 1370: q        BINPUT     29

 1372: c        GLOBAL     'zope.location.interfaces ILocation'

 1408: q        BINPUT     30

 1410: c        GLOBAL     'OFS.interfaces IManageable'

 1438: q        BINPUT     31

 1440: c        GLOBAL     'Products.CMFCore.interfaces IMinimalDublinCore'

 1488: q        BINPUT     32

 1490: c        GLOBAL     'Products.CMFCore.interfaces IMutableDublinCore'

 1538: q        BINPUT     33

 1540: c        GLOBAL     'Products.CMFCore.interfaces IMutableMinimalDublinCore'

 1595: q        BINPUT     34

 1597: c        GLOBAL     ' INameFromTitle'

 1642: q        BINPUT     35

 1644: c        GLOBAL     'App.interfaces INavigation'

 1672: q        BINPUT     36

 1674: c        GLOBAL     'Products.CMFCore.interfaces IOpaqueItemManager'

 1722: q        BINPUT     37

 1724: c        GLOBAL     'AccessControl.interfaces IOwned'

 1757: q        BINPUT     38

 1759: c        GLOBAL     'AccessControl.interfaces IPermissionMappingSupport'

 1811: q        BINPUT     39

 1813: c        GLOBAL     'persistent.interfaces IPersistent'

 1848: q        BINPUT     40

 1850: c        GLOBAL     'OFS.interfaces IPropertyManager'

 1883: q        BINPUT     41

 1885: c        GLOBAL     ' IRelatedItems'

 1933: q        BINPUT     42

 1935: c        GLOBAL     'AccessControl.interfaces IRoleManager'

 1974: q        BINPUT     43

 1976: c        GLOBAL     'plone.contentrules.engine.interfaces IRuleAssignable'

 2030: q        BINPUT     44

 2032: c        GLOBAL     'Products.CMFDynamicViewFTI.interfaces ISelectableBrowserDefault'

 2097: q        BINPUT     45

 2099: c        GLOBAL     'OFS.interfaces ISimpleItem'

 2127: q        BINPUT     46

 2129: c        GLOBAL     ' ITableOfContents'

 2196: q        BINPUT     47

 2198: c        GLOBAL     'OFS.interfaces ITraversable'

 2227: q        BINPUT     48

 2229: c        GLOBAL     'plone.uuid.interfaces IUUIDAware'

 2263: q        BINPUT     49

 2265: c        GLOBAL     'Products.CMFEditions.interfaces IVersioned'

 2309: q        BINPUT     50

 2311: c        GLOBAL     ' IVersioningSupport'

 2370: q        BINPUT     51

 2372: c        GLOBAL     'Products.CMFCore.interfaces IWorkflowAware'

 2416: q        BINPUT     52

 2418: c        GLOBAL     'OFS.interfaces IWriteLock'

 2445: q        BINPUT     53

 2447: c        GLOBAL     'OFS.interfaces IZopeObject'

 2475: q        BINPUT     54

 2477: c        GLOBAL     'zope.interface Interface'

 2503: q        BINPUT     55

 2505: c        GLOBAL     'plone.dexterity.schema.generated Plone_0_Document'

 2556: q        BINPUT     56

 2558: c        GLOBAL     'plone.supermodel.model Schema'

 2589: q        BINPUT     57

 2591: t        TUPLE      (MARK at 2)

 2592: q    BINPUT     58

 2594: \x85 TUPLE1

 2595: q    BINPUT     59

 2597: \x85 TUPLE1

 2598: q    BINPUT     60

 2600: \x85 TUPLE1

 2601: q    BINPUT     61

 2603: .    STOP

highest protocol among opcodes = 2

If you are into this you can read the pickle now :)

If you press c again zodbverify will build the refernce-tree for this object and ispect if for you:

(Pdb++) c

2020-08-24 12:22:42,596 INFO    [zodbverify:234][MainThread] ModuleNotFoundError: No module named 'webdav.interfaces'; 'webdav' is not a package: 0x3b1d06

2020-08-24 12:22:42,597 INFO    [zodbverify:43][MainThread] Building a reference-tree of ZODB...

2020-08-24 12:22:42,964 INFO    [zodbverify:60][MainThread] Objects: 10000

2020-08-24 12:22:44,167 INFO    [zodbverify:60][MainThread] Objects: 20000

2020-08-24 12:22:44,521 INFO    [zodbverify:60][MainThread] Objects: 30000

2020-08-24 12:22:44,891 INFO    [zodbverify:60][MainThread] Objects: 40000

2020-08-24 12:22:45,184 INFO    [zodbverify:60][MainThread] Objects: 50000

2020-08-24 12:22:45,507 INFO    [zodbverify:60][MainThread] Objects: 60000

2020-08-24 12:22:45,876 INFO    [zodbverify:60][MainThread] Objects: 70000

2020-08-24 12:22:46,403 INFO    [zodbverify:60][MainThread] Objects: 80000

2020-08-24 12:22:46,800 INFO    [zodbverify:60][MainThread] Objects: 90000

2020-08-24 12:22:47,107 INFO    [zodbverify:60][MainThread] Objects: 100000

2020-08-24 12:22:47,440 INFO    [zodbverify:60][MainThread] Objects: 110000

2020-08-24 12:22:47,747 INFO    [zodbverify:60][MainThread] Objects: 120000

2020-08-24 12:22:48,052 INFO    [zodbverify:60][MainThread] Objects: 130000

2020-08-24 12:22:48,375 INFO    [zodbverify:60][MainThread] Objects: 140000

2020-08-24 12:22:48,665 INFO    [zodbverify:60][MainThread] Objects: 150000

2020-08-24 12:22:48,923 INFO    [zodbverify:60][MainThread] Objects: 160000

2020-08-24 12:22:49,037 INFO    [zodbverify:61][MainThread] Created a reference-dict for 163955 objects.

2020-08-24 12:22:49,386 INFO    [zodbverify:182][MainThread] Save reference-cache as /Users/pbauer/.cache/zodbverify/zodb_references_0x03d7f331f3692266.json

2020-08-24 12:22:49,424 INFO    [zodbverify:40][MainThread] The oid 0x3b1d06 is referenced by:

0x3b1d06 (BTrees.OIBTree.OITreeSet) is referenced by 0x3b1d01 (BTrees.OOBTree.OOBucket) at level 1

0x3b1d01 (BTrees.OOBTree.OOBucket) is referenced by 0x11c284 (BTrees.OOBTree.OOBTree) at level 2

0x11c284 (BTrees.OOBTree.OOBTree) is _reltoken_name_TO_objtokenset for 0x11c278 (z3c.relationfield.index.RelationCatalog) at level 3

0x11c278 (z3c.relationfield.index.RelationCatalog) is relations for 0x1e (five.localsitemanager.registry.PersistentComponents) at level 4

0x1e (five.localsitemanager.registry.PersistentComponents) is referenced by 0x11 (Products.CMFPlone.Portal.PloneSite) at level 5

0x11 (Products.CMFPlone.Portal.PloneSite) is Plone for 0x01 (OFS.Application.Application) at level 6

8< --------------- >8 Stop at root objects

0x11 (Products.CMFPlone.Portal.PloneSite) is Plone for 0x02f6 (persistent.mapping.PersistentMapping) at level 7

8< --------------- >8 Stop at root objects

0x11 (Products.CMFPlone.Portal.PloneSite) is Plone for 0x02f7 (zope.component.persistentregistry.PersistentAdapterRegistry) at level 8

8< --------------- >8 Stop at root objects

0x1e (five.localsitemanager.registry.PersistentComponents) is __parent__ for 0x02f5 ( at level 6

0x1e (five.localsitemanager.registry.PersistentComponents) is __parent__ for 0x02fa (zope.ramcache.ram.RAMCache) at level 7

0x1e (five.localsitemanager.registry.PersistentComponents) is __parent__ for 0x02fd ( at level 8

0x02fd ( is __parent__ for 0x338f13 ( at level 9

0x338f13 ( is ++rule++rule-2 for 0x0303 (BTrees.OOBTree.OOBTree) at level 10

0x02fd ( is __parent__ for 0x346961 ( at level 10

0x02fd ( is __parent__ for 0x346b59 ( at level 11

0x02fd ( is __parent__ for 0x346b61 ( at level 12

0x1e (five.localsitemanager.registry.PersistentComponents) is __parent__ for 0x02fe ( at level 9

0x1e (five.localsitemanager.registry.PersistentComponents) is referenced by 0x034d (plone.keyring.keyring.Keyring) at level 10

0x034d (plone.keyring.keyring.Keyring) is referenced by 0x02fb (persistent.mapping.PersistentMapping) at level 11

0x02fb (persistent.mapping.PersistentMapping) is referenced by 0x3b1a32 (plone.keyring.keyring.Keyring) at level 12

0x02fb (persistent.mapping.PersistentMapping) is referenced by 0x3b1a33 (plone.keyring.keyring.Keyring) at level 13

0x1e (five.localsitemanager.registry.PersistentComponents) is __parent__ for 0x3b3dc4 (pas.plugins.ldap.plonecontrolpanel.cache.CacheSettingsRecordProvider) at level 11

0x3b1d01 (BTrees.OOBTree.OOBucket) is _next for 0x3b1cf1 (BTrees.OOBTree.OOBucket) at level 3


From this output you can find out that the broken object is (surprise) a item in the RelationCatalog of zc.relation. See the chapter "Frequent Culprits" for information how to deal with these.

Example 1 of using

In this and the next example I will use the script to find out where a broken objects actually sits so I can remove or fix it. The easier approach is to use zodbverify but I discuss this approach here since it was your best option until I extended zodbverify and since it might help you to understand the way references work in the ZODB.

$ ./bin/zodbverify -f var/filestorage/Data.fs

INFO:zodbverify:Done! Scanned 120797 records.

Found 116 records that could not be loaded.

Exceptions and how often they happened:

AttributeError: Cannot find dynamic object factory for module plone.dexterity.schema.generated: 20

AttributeError: module '' has no attribute 'IEventSettings': 3

ModuleNotFoundError: No module named 'Products.ATContentTypes': 4

ModuleNotFoundError: No module named 'Products.Archetypes': 5

ModuleNotFoundError: No module named 'Products.CMFDefault': 20

ModuleNotFoundError: No module named 'Products.CMFPlone.DiscussionTool': 1

ModuleNotFoundError: No module named 'Products.CMFPlone.MetadataTool': 1

ModuleNotFoundError: No module named 'Products.PloneLanguageTool': 1

ModuleNotFoundError: No module named 'Products.ResourceRegistries': 1

ModuleNotFoundError: No module named 'fourdigits': 8

ModuleNotFoundError: No module named '': 2

ModuleNotFoundError: No module named ''; '' is not a package: 34

ModuleNotFoundError: No module named 'webdav.EtagSupport'; 'webdav' is not a package: 16

Follow the white rabbit...

./bin/zopepy ./parts/packages/ZODB/scripts/ var/filestorage/Data.fs 0x35907d

oid 0x35907d BTrees.OIBTree.OISet 1 revision

    tid 0x03c425bfb4d8dcaa offset=282340 2017-12-15 10:07:42.386043

        tid user=b'Plone'

        tid description=b'/Plone/it-service/hilfestellungen-anleitungen-faq/outlook/content-checkout'

        new revision BTrees.OIBTree.OISet at 282469

    tid 0x03d3e83a045dd700 offset=421126 2019-11-19 15:54:01.023413

        tid user=b''

        tid description=b''

        referenced by 0x35907b BTrees.OIBTree.OITreeSet at 911946038


Follow referenced by ...

./bin/zopepy ./parts/packages/ZODB/scripts/ var/filestorage/Data.fs 0x35907b


referenced by 0x3c5790 BTrees.OOBTree.OOBucket
./bin/zopepy ./parts/packages/ZODB/scripts/ var/filestorage/Data.fs 0x3c5790


referenced by 0x11c284 BTrees.OOBTree.OOBTree

./bin/zopepy ./parts/packages/ZODB/scripts/ var/filestorage/Data.fs 0x11c284


referenced by 0x3d0bd6 BTrees.OOBTree.OOBucket

./bin/zopepy ./parts/packages/ZODB/scripts/ var/filestorage/Data.fs 0x3d0bd6


referenced by 0x11c278 z3c.relationfield.index.RelationCatalog


Found it!!!!!

Example 2 of using

In this example zodbverify found a trace of Products.PloneFormGen even though you think you safely uninstalled the addon (e.g. using

Then find out where exists in the tree by following the trail of items that reference it:

./bin/zopepy ./parts/packages/ZODB/scripts/ var/filestorage/Data.fs 0x372d00

oid 0x372d00 Products.PloneFormGen.content.thanksPage.FormThanksPage 1 revision

    tid 0x03d3e83a045dd700 offset=421126 2019-11-19 15:54:01.023413

        tid user=b''

        tid description=b''

        new revision Products.PloneFormGen.content.thanksPage.FormThanksPage at 912841984

        referenced by 0x372f26 BTrees.OIBTree.OIBucket at 912930339

        references 0x372e59 Products.Archetypes.BaseUnit.BaseUnit at 912841984

        references 0x372e5a Products.Archetypes.BaseUnit.BaseUnit at 912841984

        references 0x372e5b OFS.Folder.Folder at 912841984

        references 0x372e5c Products.Archetypes.BaseUnit.BaseUnit at 912841984

        references 0x372e5d Products.Archetypes.BaseUnit.BaseUnit at 912841984

        references 0x372e5e Persistence.mapping.PersistentMapping at 912841984

    tid 0x03d40a3e52a41633 offset=921078960 2019-11-25 17:02:19.368976

        tid user=b'Plone pbauer'

        tid description=b'/Plone/rename_file_ids'

        referenced by 0x2c1b51 BTrees.IOBTree.IOBucket at 921653012

Follow referenced by until you find something...

./bin/zopepy ./parts/packages/ZODB/scripts/ var/filestorage/Data.fs 0x2c1b51

oid 0x2c1b51 BTrees.IOBTree.IOBucket 1 revision


Here I skip the trail of referenced by until I find 0x280184 five.intid.intid.IntIds:

./bin/zopepy ./parts/packages/ZODB/scripts/ var/filestorage/Data.fs 0x280184

oid 0x280184 five.intid.intid.IntIds 1 revision

    tid 0x03d3e83a045dd700 offset=421126 2019-11-19 15:54:01.023413

        tid user=b''

        tid description=b''

        new revision five.intid.intid.IntIds at 8579054

        references 0x28018c <unknown> at 8579054

        references 0x28018d <unknown> at 8579054

    tid 0x03d3e90c4d3aed55 offset=915868610 2019-11-19 19:24:18.100824

        tid user=b' adminstarzel'

        tid description=b'/Plone/portal_quickinstaller/installProducts'

        referenced by 0x02f6 persistent.mapping.PersistentMapping at 915868690

        referenced by 0x02f7 zope.component.persistentregistry.PersistentAdapterRegistry at 915879394

        referenced by 0x02f7 zope.component.persistentregistry.PersistentAdapterRegistry at 915879394

        referenced by 0x1e five.localsitemanager.registry.PersistentComponents at 915898834

That is the IntId-Catalog from zope.intid. The problem seems to be that similar to the zc.relation catalog rerefences to broken objects stay in the catalog and need to be removed manually.

Here is a example of how to remove all broken objects from the catalog in a pdb-session:

(Pdb++) from zope.intid.interfaces import IIntIds

(Pdb++) from zope.component import getUtility

(Pdb++) intid = getUtility(IIntIds)

(Pdb++) broken_keys = [i for i in intid.ids if 'broken' in repr(i.object)]

(Pdb++) for broken_key in broken_keys: intid.unregister(broken_key)


(Pdb++) import transaction

(Pdb++) transaction.commit()

After packing the DB the problem is gone. o/

Other Options

Use zodbbrowser to inspect the ZODB.
It is Zope3 app to navigate a ZODB in a browser. At least I had problems getting it to run with a Plone-ZODB.
Use zc.zodbdgc
This tool can validate distributed databases by starting at their root and traversing to make sure all referenced objects are reachable. Optionally, a database of reference information can be generated.
Use collective.zodbdebug
A great tool to build and inspect reference-maps and backreference-maps of a ZODB. So for it does not work with Python 3 yet. Some if its features are also part of zodbverify.

Frequent Culprits

IntIds and Relations

The IntId-Tool and the relation-catalog are by far the most requent issues, especially if you migrated from Archetypes to Dexterity.

There may be a lot of RelationValues in these Tools that still reference objects that cannot be loadedif these removed objects were not properly removed.

The following code from collective.relationhelpers cleans up the IntId- and Relation-catalog but keeps relations intact. For large sites it may take a while to run because it also needs to recreate linkintegrity-relations.

from collective.relationhelpers.api import cleanup_intids

from collective.relationhelpers.api import purge_relations

from collective.relationhelpers.api import restore_relations

from collective.relationhelpers.api import store_relations

def remove_relations(context=None):

    # store all relations in a annotation on the portal


    # empty the relation-catalog


    # remove all relationvalues and refs to broken objects from intid


    # recreate all relations from a annotation on the portal


For details see


Many addons and features in Plone store data in Annotations on the portal or on content.

It's a good idea to check IAnnotations(portal).keys() after a migration for Annotation that you can safely remove.

Here is a example where wicked (the now-removed wiki-style-editing feature of Plone) stored it's settings in a Annotation:

def cleanup_wicked_annotation(context=None):

    ann = IAnnotations(portal)

    if '' in ann:

        del ann['']

Another example is files from failed uploads stored by plone.formwidget.namedfile in a annotation:

def cleanup_upload_annotation(context=None):

    # remove traces of aborted uploads

    ann = IAnnotations(portal)

    if ann.get('file_upload_map', None) is not None:

        for uuid in ann['file_upload_map']:

            del ann['file_upload_map'][uuid]


Migrating a ZODB from py2 to py3

Since people often encounter issues with their ZODB after migrating here is a quick dive into migrating a ZODB from Python 2 to Python 3.

The migration is basically calling the script zodbupdate in py3 with the parameter --convert-py3.

$ ./bin/zodbupdate --convert-py3

You need to pass it the location of the database, the defaul-encoding (utf8) and a fallback-encoding (latin1) for items where decoding to utf8 fails.


$ ./bin/zodbupdate --convert-py3 --file=var/filestorage/Data.fs --encoding=utf8 --encoding-fallback latin1

Updating magic marker for var/filestorage/Data.fs

Ignoring index for /Users/pbauer/workspace/projectx/var/filestorage/Data.fs

Loaded 2 decode rules from AccessControl:decodes

Loaded 12 decode rules from OFS:decodes

Loaded 2 decode rules from Products.PythonScripts:decodes

Loaded 1 decode rules from Products.ZopeVersionControl:decodes

Committing changes (#1).

After that you should be able to use your ZODB in Python 3.

The process in a nutshell:

  1. First, run bin/zodbupdate -f var/filestorage/Data.fs So no python3 convert stuff yet! This will detect and apply several explicit and implicit rename rules.
  2. Then run bin/instance zodbverify. If this still gives warnings or exceptions, you may need to define more rules and apply them with zodbupdate. But you can still choose to migrate to py3 if this shows errors.
  3. Using Python 3 run bin/zodbupdate --convert-py3 --file=var/filestorage/Data.fs --encoding utf8
  4. For good measure, on Python 3 run bin/instance zodbverify.

Read the docs:

See also:

Dealing with oids

Transforming oids from int to hex and text and vice versa:

>>> from ZODB.utils import p64

>>> oid = 0x2c0ab6

>>> p64(oid)


>>> from ZODB.utils import oid_repr

>>> oid = b'\x00\x00\x00\x00\x00,\n\xb6'

>>> oid_repr(oid)


>>> from ZODB.utils import repr_to_oid

>>> oid = '0x2c0ab6'

>>> repr_to_oid(oid)


Get a path for blobs:

from ZODB.blob import BushyLayout

if isinstance(oid, int):

    # e.g. oid = 0x2c0ab6

    from ZODB.utils import p64

    oid = p64(oid)

return BushyLayout.oid_to_path(None, oid)

Load a obj by oid from ZODB in a pdb-prompt:

oid = 0x2c0ab6

from ZODB.utils import p64

app = self.context.__parent__

obj = app._p_jar.get(p64(oid))


Finish, merge and document


Quite a lot of people from the Plone/Zope communities have wriotten about this issue. I learned a lot from these posts: