Automatically Delete Old Pa11y Results From MongoDB

You’ve probably already noticed that Pa11y-Dashboard runs all the tasks on a daily basis. If you have a lot of tasks (e.g. 100+) then the test results can fairly quickly gobble up your MongoDB quota (if you have any).

If your MongoDB has a size limit defined, then you can do two things:

• manually delete old test results
• or use TTL Index to do it for you automagically

MongoDB supports TTL indexes since v2.2 (Aug 2012!). Such indexes make mongod automatically remove data after a specified number of seconds or at a specific clock time. Before we create one, please have a look at existing indexes for Pa11y test results collection:

db.results.getIndexes()
[
    {
        "v" : 2,
        "key" : {
            "_id" : 1
        },
        "name" : "_id_",
        "ns" : "heroku_abcdefgh.results"
    },
    {
        "v" : 2,
        "key" : {
            "date" : 1
        },
        "name" : "date_1",
        "ns" : "heroku_abcdefgh.results"
    }
]

There should be two indexes. We’re interested in the date_1 index. We have to remove it before we can add a TTL Index:

db.results.dropIndex({"date": 1});

In my case I wanted to keep tests results for the last 31 days.
So TTL value (expireAfterSeconds) should be set to 2678400 (60*60*24*31).

db.results.createIndex({"date": 1}, {expireAfterSeconds: 2678400});

Let’s have a look at the indexes:

db.results.getIndexes()
[
    {
        "v" : 2,
        "key" : {
            "_id" : 1
        },
        "name" : "_id_",
        "ns" : "heroku_abcdefgh.results"
    },
    {
        "v" : 2,
        "key" : {
            "date" : 1
        },
        "name" : "date_1",
        "ns" : "heroku_abcdefgh.results",
        "expireAfterSeconds" : 2678400
    }
]

LGTM!

Now, we have to wait a month before we can check if it works as expected ;)

Backing up the task

Remember to back-up your Pa11y tasks (and results) before every major upgrade or DB operation.
It takes few seconds to do it and it can save you a lot of time and stress.

mongoexport \
    --uri=mongodb://username:password@host:61620/heroku_abcdefgh \
    -c tasks \
    -o tasks.json