In order to update counters, we’ll need to store the actual counter information. For each counter and precision, like site hits and 5 seconds, we’ll keep a HASH that stores information about the number of site hits that have occurred in each 5-second time slice. The keys in the hash will be the start of the time slice, and the value will be the number of hits. Figure 5.1 shows a selection of data from a hit counter with 5-second time slices.
As we start to use counters, we need to record what counters have been written to so
that we can clear out old data. For this, we need an ordered sequence that lets us iterate
one by one over its entries, and that also doesn’t allow duplicates. We could use a LIST
combined with a SET, but that would take extra code and round trips to Redis. Instead,
we’ll use a ZSET, where the members are the combinations of precisions and names that
have been written to, and the scores are all 0. By setting all scores to 0 in a ZSET, Redis
will try to sort by score, and finding them all equal, will then sort by member name. This gives us a fixed order for a given set of members, which will make it easy to sequentially
scan them. An example ZSET of known counters can be seen in figure 5.2.
Figure 5.1A HASH that shows the number of web page hits over 5-second time slices around 7:40 a.m. on May 7, 2012Figure 5.2A ZSET that shows some known counters
Next, if we look closer we can see there are 4 requests being generated to fonts.gstatic.com. And this is to load Google fonts, which is included in the default WordPress theme. In our example, it is loading different font weights for Merriweather and Montserrat.
It always better to reduce the number of external DNS lookups and also focus on having a single HTTP/2 connection if possible. Every external lookup introduces its own set of latency issues, content download times, TLS negotiations, etc. So what we are going to do is move the Google fonts to our CDN. This way they load from the same place as the rest of our assets.
You can check out our in-depth tutorial on how to migrate Google Fonts to your CDN. This can also be used to simply host them directly on your web server as well, if you aren’t using a CDN. We quickly download the following Google fonts from https://google-webfonts-helper.herokuapp.com and host them on our server in a folder called “fonts.”
As you can see we are almost down to a single HTTP/2 connection with no external DNS lookups. The only thing left is that call to gravatar.com. Thankfully they are using HTTP/2 now, but unless you really want avatars, you can disable them.
This can easily be remove by un-checking the “show avatars” in the discussion setting of your WordPress dashboard.
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By removing the call to gravatar.com we are now down to 11 HTTP requests and are using a single HTTP/2 connection for external assets on our CDN.
