perf: create index for Jobs queries

[aldeed]

Impact: minor
Type: performance

Issue

In profiling DB ops locally, I noticed that the job-queue package does periodic queries of the Jobs collection with only status and expiresAfter as query fields. These queries do a COLLSCAN, which can be very slow as the number of jobs increases.

Solution

Added a { status: 1 } index on Jobs collection.

Breaking changes

None

Testing

Check out develop branch.

First run db.setProfilingLevel(2) in your local DB Mongo shell. This will tell it to log all queries.

Now start the app, wait a minute, and run this query:

db.system.profile.find({ 
    "command.find" : "Jobs", 
    "command.filter.status" : "running"
}).sort({ 
    "ts" : -1.0
});

You should see planSummary field is COLLSCAN on these queries.

Now check out this PR branch, start the app, wait a minute, and run the above query again. You should see planSummary field is "IXSCAN { status: 1 }" on the most recent one.

Finally, run db.setProfilingLevel(0) to turn off profiling since it will slow down your local DB.

[rosshadden]

LGTM 👍