One of my client websites suddenly started giving an error: Error establishing a database connection. When I went to the /wp-admin URL, the error was still there.

This particular website is on shared hosting, so I logged into the CPanel and checked the database was still there. Then I checked the database and found some issues with some of the tables.

[site.wp_links] error: Table upgrade required. Please do "REPAIR TABLE wp_links" or dump/reload to fix it!
[site.wp_options] error: Table upgrade required. Please do "REPAIR TABLE wp_options" or dump/reload to fix it!
[site.wp_postmeta] status: OK
[site.wp_posts] status: OK
[site.wp_term_relationships] status: OK
[site.wp_term_taxonomy] error: Table upgrade required. Please do "REPAIR TABLE wp_term_taxonomy" or dump/reload to fix it!
[site.wp_terms] status: OK
[site.wp_usermeta] error: Table upgrade required. Please do "REPAIR TABLE wp_usermeta" or dump/reload to fix it!
[site.wp_users] error: Table upgrade required. Please do "REPAIR TABLE wp_users" or dump/reload to fix it!


Running those SQL queries on the appropriate database in phpMyAdmin fixed the problem. I don’t know whether the hosting company upgraded the database, or something happened with the automatic WordPress upgrade system, or if something else caused the problem.

[Update] There were a bunch of other errors that cropped up afterwards with the White Screen of Death; I had to call the hosting company to sort out the server-side errors causing those. It’s possible those errors were the original cause of the database problems, whatever they were.

I discovered another issue while deploying to PythonAnywhere (maybe it’s applicable to other PAAS providers as well).

There was an odd ImportError when running manage.py. In the specific case I had, it showed up when running the tests with coverage: from Unipath import Path ImportError: No module named ‘Unipath’. It turned out I hadn’t installed coverage in the virtual environment, which meant the system was using the default one. Installing coverage in the virtual environment as well fixed the problem.

A checklist for moving a Django-Wagtail project to PythonAnywhere. There is documentation on the PythonAnywhere site; mine includes things I forget.

Setup: development and testing on my laptop, staging and production on PythonAnywhere.

The help files are pretty good, but I need my own checklist. Right now I’m in the staging mode, but at some stage I’ll be moving to production. No point figuring out the same things twice!

1. Develop on laptop in a virtualenv. Push commits regularly to bitbucket account. At some stage squash the migrations and clean those up. Four sets of settings: dev, testing, staging, production.
2. Set up account on PythonAnywhere that allows the use of Postgres (it’s an add-on to a custom plan).
3. Create virtualenv and set up staging web app. Delete virtualenv when you realise you didn’t use the right version of Python and the default is 2.7, not 3.5. Recreate the virtualenv with python 3.5.
4. Clone the repository (using the ssh-keygen instructions). Redirect the public key to a file so you can copy it without line-breaks getting in the way.
5. pip install -r requirements/production.txt (including psycopg2, which I didn’t need for development).
6. Create the Postgres server, user, and database Don’t forget a strong password for the user (owner of the project database).
7. Update the settings file with the database settings.
8. Set the environment variables for the settings and the secret key (generator).
9. Attempt to apply the migrations. This will show where you made mistakes on all the preceding steps.
10. Fix the mistakes. Reload the web app to see if anything shows up.
11. Set up the static file server. Check the static files are being served correctly.

The next step is data, of course.

WordPress was designed for public websites, not private ones, so password protection can be a little clunky. Fortunately there are plugins to help, but (as always) there are trade-offs to be made.

When all you want to do is add a password to stop search engines indexing and outsiders reading the content, but you also want make it as easy as possible for people to use, there’s the Password Protected plugin. As it says, it doesn’t protect the images or other uploaded content.

Two-factor authentication is generally seen as a good idea; there’s a certain amount of hand-wringing over the fact that more people don’t turn it on. The problem is, it’s one of those things where you sign up for disruption over the next few days, for uncertain reward. The reward is uncertain because you can never tell whether turning on two-factor authentication stopped someone hacking your account or not, just like you can’t tell whether having an alarm company sign outside your house dissuades someone from breaking into it. My main email account has been on 2FA for ages, but I decided to add it to one of my secondary accounts as well, given that lots of people seem to mistakenly use that email instead of their own.

Tim suggested I used the authenticator app for my Google account 2FA, instead of using the SMS system. Just a hint: set it up while you still have access to your text messages since SMS is used for the bootstrapping authentication. You need to sign up for Google 2FA in the first place ‘on a computer’ (not specified whether a tablet is sufficient? I used the desktop). You are sent an SMS to authenticate yourself, and then you get another one when you want to authenticate the Authenticator app. After that, you don’t need your SMS system, as long as you have the device with the Authenticator app on it.

But then there are the other apps, which now need application-specific generated passwords. Adium for Google Talk, for example, or email with Thunderbird. Setting each one up doesn’t take long, but I’m sure some time in the future I will have forgotten and be wondering why I can’t log in with a valid password.

And I understand what’s going on, more or less, and think the short-term hassles are worth it. There are lots of people who don’t have a mental model of passwords or authentication, who see only the pain and not the gain (since the gain is only in the absence of a potential future pain). Businesses are supposedly implementing 2FA fairly rapidly, but I’d be surprised if people in general were outfitting their personal accounts with 2FA at anything like the same rate. Mind you, I also suspect those surveys apply mostly to bigger companies in particular industries; anecdotal evidence I’ve heard points to a lower real adoption rate.

I've been working at Design Science for a couple of months now, as Senior Product Manager concentrating on the MathFlow products. So I figured I should enable MathML support on my blog. It's not hard, but like everything in tech there are a few niggly details. Many of those issues are caused by WordPress's over-eager helpfulness, which has to be reined in on a regular basis if you're doing anything at all out of the ordinary. Like editing your posts directly in HTML rather than using some pseudo-WYSIWYG editor.

Theoretically, showing MathML in a browser is easy, at least for the sort of equations that most people put in blog posts, even though not all browsers support MathML directly. You just use the MathJax JavaScript library. On WordPress there is even a plugin that adds the right script element, the MathJax-Latex plugin. You can make every page load MathJax, or use the [mathjax] shortcode to tell it when to load.

The wrinkle comes with WordPress' tendency to "correct" the markup. When you add the MathML, WordPress sprinkles it with <br/> tags. MathJax chokes on those and shows nothing. Since the tags don't show up in the editor view, you need some way of stopping WordPress from adding them. The best way I've found is with the Raw HTML plugin.

But there's a wrinkle with that too. For some reason if you use the shortcode version of the begin and end markers ([raw]) the editor decides that the XML characters between those markers has to be turned into the character entities, so for example the < characters are turned into &lt;. To stop that, you need to a) check all the checkboxes in the Raw HTML settings on the post, and b) use the comment version (<-- raw --> and <-- /raw -->) to mark the beginning and end of the section instead of the shortcode version.

Once it's done it's easy to add equations to your pages, so it's worth the extra few minutes to set it all up.

A couple of examples taken from the MathJax samples page

Curl of a Vector Field
$∇→×F→=(∂Fz∂y−∂Fy∂z)i+(∂Fx∂z−∂Fz∂x)j+(∂Fy∂x−∂Fx∂y)k$
Standard Deviation
$σ=1N∑i=1N(xi−μ)2$

and one from my thesis from way back when

$fλ=n!⁢∏i
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