Compositing in Plone

Seven years ago, I started a project called CompositePage.  It added a drag and drop UI to Zope 2.  Others built on it and created CompositePack.  I applaud them for their efforts.

However, today I think the CompositePage UI pattern is the wrong idea.  The CompositePage UI pattern is to render the page with extra markup that allows people with the necessary privileges to move objects around the page.  The idea works technically, but it incurs a lot of technical issues for template authors and it is frequently difficult to explain to users.

I saw an implementation of a much better idea a few years ago.  The better idea is to present a greatly simplified representation of the page when in design mode.  Ideally, the simplified page should contain only basic colors and fuzzy text, so as to draw the user’s attention to the widgets, not the page.

Now it just occurred to me that CompositePage could implement this idea easily by letting developers define two templates per layout: the real template and the representative design template.  Why didn’t I think of that before?  That would be quite friendly.

RelStorage 1.4.0b1 and zodbshootout

I just released RelStorage 1.4.0b1.  New features:

  • More documentation.
  • Support for history-free storage on PostgreSQL, MySQL, and Oracle.  This reduces the need to pack and makes RelStorage more appropriate for session storage.
  • Speed.  New tests prompted several optimizations that reduced the effect of network latency in both read and write operations.  Memcached support is now integrated in a much better way.
  • Support for asynchronous database replication.  Previous versions of RelStorage worked with MySQL replication, but did not keep ZODB caches in sync when failing over to a slave that was slightly out of date.
  • The Oracle adapter now uses PL/SQL for speed and lock timeouts.  Lock timeouts are important for preventing cluster lockup.
  • Moved the speed test script into a separate package named zodbshootout, making it easier for developers and administrators to run comparative performance tests.
  • The adapter code is more modular, making it easier to support new kinds of databases and database adapter modules.

The zodbshootout script tells me this release of RelStorage is faster than ever.  It reports objects read or written per second, so unlike the previous charts I’ve made, bigger is now better.  Here are the results:


PostgreSQL now beats MySQL in some of the tests.  Oracle (not on this chart) is now looking pretty good too.

The new features led to far more automated tests.  My private Buildbot, which tests RelStorage with several combinations of Python, ZODB, and operating systems (in virtual private servers), now takes 2 hours to run all the tests.  Maybe I need to upgrade that server or investigate the possibility of making Buildbot launch an Amazon EC2 instance.

The previous release was 1.3.0b1, which added ZODB blob support.  Several customers asked for new features right after I released 1.3.0b1, so I decided to jump to version 1.4.0b1 rather than finalize the 1.3 series.  The 1.2 series has had more extensive testing, so use that for a while if you have troubles with 1.4.0b1.

This new release should be particularly interesting for Plone users, since Plone is always hungry for faster infrastructure.

PyCon 2010: I Want to Present Something

I’ve been racking my brains to find something to present at PyCon 2010. I have been trying to find something good to present since PyCon 2003, when I last presented at PyCon.  (I talked about Ape, the Adaptable Persistence Engine for Zope.)  I really liked the experience of presenting and it led to a lot of interesting conversations. Since then, however, nothing has really struck me as a good idea for a presentation. The right idea has to fit at least these criteria:

  • It’s something I’m good at.
  • At least a handful of PyCon attendees would like to learn more about it in a presentation.
  • I can’t spend weeks to prepare for the presentation.

This year, I was planning to do a really fun presentation by writing some Python scripts for controlling a RepRap, then I was going to present the hardware and software.  That didn’t work out, however, because the warping issues with ABS (a type of plastic) are just too severe to print useful parts, so my RepRap has sat idle.  (I’m now considering PLA, but it’s a newish and expensive material.)

Here are a few other ideas for a presentation topic.  What do you think?  Any other ideas?

  • RelStorage.  I could talk about future plans, why I think it is an improvement over ZEO, and why you should use it.  There seem to be a lot of people with questions about RelStorage, so it would be nice to have some time to answer the questions in a big room so others can hear the answers.
  • KARL and BFG.  This would probably be a team presentation.  KARL is some fairly interesting software that I got to help develop this year.  I could talk about the software, along with the development experience and style.  In KARL we made a conscious choice to ignore certain apparent DRY violations, leading to significant productivity gains.
  • A friendly introduction to Buildout.  Buildout is a tool that a lot of developers need, but don’t know it yet.  The function that Buildout performs is as important as version control and automated testing.  Come find out why Buildout is far better than a pile of Makefiles.
  • An introduction to Buildout (zc.buildout) for people familiar with Apache Maven.  Buildout and Maven fill approximately the same niche, but for different audiences.  (Buildout for Python, Maven for Java.)  Maybe there are Mavenites at the conference who would like to switch to a more Python centric system.
  • A discussion of text indexing in Plone and BFG.  This might be a narrow topic, but I find it interesting and important.  I have found ways to reduce complex 90 second text searches to 1 second.  The solution is not pure Python, unfortunately. 😉  I have also thought about how to expand into areas like faceted search/browse functionality.

Feedback encouraged!

RelStorage 1.3.0b1, Now With Blob Support

I have just released two versions of RelStorage. Version 1.3.0b1 adds full support for ZODB blobs stored on the filesystem. Version 1.2.0 is currently the better choice if you’re upgrading a production system and don’t need blob support.

People have been asking for blob support for months. I am glad to finally get it done, with a little help from a customer. With blob support, now we can easily store large artifacts on the filesystem, while keeping all metadata in the database.

To celebrate the new release, I have created a sample buildout.cfg that builds Plone with RelStorage, PostgreSQL, and blob support. (Thanks goes to Hanno Schlichting, who released a compatible version of plone.recipe.zope2instance only moments after I requested it.) Here it is:

parts = plone zope2 instance zopepy
find-links =
eggs =
versions = versions

ZODB3 = 3.8.3-polling
RelStorage = 1.3.0b1

recipe = plone.recipe.plone

recipe = plone.recipe.zope2install
url = ${plone:zope2-url}

recipe = plone.recipe.zope2instance
zope2-location = ${zope2:location}
user = admin:admin
products = ${plone:products}
eggs =
zcml =
rel-storage =
    type postgresql
    dsn dbname='plone' user='plone' host='localhost' password='plone'
    blob-dir var/blobs

recipe = zc.recipe.egg
eggs = ${instance:eggs}
interpreter = zopepy
extra-paths = ${instance:zope2-location}/lib/python
scripts = zopepy zodbconvert

P.S. I have been told that a very prominent Plone developer recently configured RelStorage with master/slave replication on MySQL, and that it works smoothly. I expect him to announce his success soon!

Book Review: Practical Plone 3

Packt Publishing asked me to review their new book, Practical Plone 3: A Beginner’s Guide to Building Powerful Websites. The book impressed me, but not in the way I expected at first.

As I read the instructions in chapter two about how to install Plone, I considered the experience my Dad would have gone through if he had this book when we were setting up Plone to run his company’s web site. My Dad is a power user, but not a programmer or systems administrator, so with this book, he probably would have installed Plone himself on a spare Windows computer. This book would have provided him enough direction to set up a lot of the functionality he needed, without my help. He would have immediately started publishing pages with Plone’s many features.

However, I imagine that a short time later, something would go seriously wrong. The computer’s IP address would change because the DHCP lease expired, the database would lose some transactions due to some misbehaving application, or a mischevious virus would rename files with a “py” extension to “rb”. All of those problems are outside Plone’s control, so this book does not try to address them.

Plone beginners like my Dad are not prepared to handle the problems that occur when a computer is used as a web server. In that light, I wondered if it really is possible to run Plone (or any content management system) without deep technical experience. I thought for a moment that this book is not for beginners after all.

Even after that logic, I decided I still want very much to give my Dad a copy of this book next time we set up a Plone web site. He will read it to find out what the latest version of Plone can do. He will install it on his own computer for his own education, but I will set up the production web site on a server.

The first twelve chapters (250 pages) are intended for Plone users. Beginners will enjoy all of those chapters, I think. As I read them, I even picked up a few things I haven’t learned, like how to use content rules.

I think beginners might struggle the most with chapter nine, which explains how to control workflow. Controlling workflow in Plone is not as easy as other Plone functions, because Plone falls back to the less polished Zope Management Interface for workflow design. Matt Bowen handled the difficult topic gracefully.

The rest of the book (almost 300 pages) is for developers, not power users. The contrast is sharp. While the first half of the book tells the reader what buttons to push, the second half tells the reader how to modify their Buildout configuration and what to type in a terminal session.

Each chapter is written by a different author. I noticed two interesting effects of multiple authorship. First, each author is enthusiastic about the particular topic, so even LDAP (which I generally find quite boring) gets a chapter of quality treatment. Second, there is more redundancy than you would find in most technical books, but redundancy is probably good in this case.

I do have one quibble with the book’s organization. When the technology behind Plone was invented, CSS was still a baby and browsers did not support it well. Back then, changing a site’s appearance meant changing nested tables in HTML, so the developers of Zope (including myself) invented ways to manage that task. That is how the portal_skins tool came about. The theming chapters explain how to use the latest version of that technology.

Today, we can expect all of our customers to use browsers that support CSS, so the chapters on theming should start by explaining how to customize the web site’s CSS. Developers will make much faster progress that way than if they have to learn the many theming-related abstractions Plone has today.

In conclusion, Practical Plone 3 is more than just a beginner’s book. I plan to use this book as a communication tool with my Plone customers. The book is a menu telling my customers who are beginners to Plone what we can set up together without a lot of work. I will also use it to help developers come up to speed on Plone.

RelStorage 1.2.0b2 Released

This release works with unpatched versions of ZODB 3.9!  A big thank-you to Jim Fulton for including support for RelStorage in ZODB.  This release also continues to support patched versions of ZODB 3.7 and 3.8.

I have been doing a lot of testing, and I have found MySQL 5.1.34 to be a lot more stable than earlier releases of MySQL 5.1, so I am now declaring MySQL 5.1.34 and above supportable, meaning that if you ask questions about it, I am no longer going to request that you revert to MySQL 5.0. 🙂

Finally, I recently expanded my private RelStorage Buildbot to include a Windows XP slave.  After solving a couple of minor test glitches, the test results are now all consistently green on 4 platforms:

  • Debian Etch, 32 bit (Python 2.4.4, MySQL 5.0.32, PostgreSQL 8.1.17, Oracle 10g XE)
  • Debian Lenny, 32 bit (Python 2.5.2, MySQL 5.0.51a, PostgreSQL 8.3.7, Oracle 10g XE)
  • Debian Lenny, 64 bit (same as above but no Oracle)
  • Windows XP, 32 bit (Python 2.6.2, MySQL 5.1.34, PostgreSQL 8.3.7)

I’m thinking about adding another Linux slave that runs MySQL 5.1 and Python 2.6.

Anyway, enjoy the release!

P.S. You may be wondering why I released 1.2.0b2 instead of 1.2.0b1.  A little slip ruined the web page on PyPI, so I fixed the slip and skipped to the next version number.

How to Install Plone with RelStorage and MySQL

These step by step instructions describe how to install Plone on Ubuntu with RelStorage connected to MySQL as the main database. Familiarity with Linux systems administration is expected. Update: These instructions were revised in August 2009 for Plone 3.2.3 and RelStorage 1.2.0.

Continue reading How to Install Plone with RelStorage and MySQL

RelStorage for Sessions?

I’ve been working on a document explaining how to install Plone with RelStorage, starting from a basic Linux server.  As always, the basic procedure is simple, but there are all sorts of interesting little complications.  One detail that bugged me today is the need for a shared session database.

Session storage is a little different from normal storage because keeping a history of session state becomes expensive quickly.  For session storage, I think we still want all the goodness of ZODB transactions, conflict detection, distributed caching, and so on, but in this case, the ability to undo is pointless and the need to pack is a liability.

The database schema I’ve been using in RelStorage is a mismatch for this need.  A history-free storage should not have a “transaction” table, there should be no need for MD5 sums and prev_tid pointers, and the compound primary keys consisting of oid and tid should become simple primary keys indexed by oid.  A history-free storage still needs garbage collection, but not packing.

I’m thinking that the main RelStorage class will need few changes to support history-free storages, while the database adapter class will change so much that it would be best to just create a different adapter.  I like that.  It won’t be possible to switch history on and off without an export and import operation, but that seems reasonable.  To put a positive spin on the new adapters, I think I’ll call the new adapters “packless”, like the old BerkeleyDB storage.

I think that’s a good plan.  While the purpose of the packless adapters is initially session storage, they will certainly be also usable for other databases, including the main database.  I expect them to be slightly simpler and faster than the history-preserving adapters we have now.

I encourage anyone interested to leave a comment, even if all you wish to say is “I want that!” 🙂