Over the past several days I have noticed a bunch of SEOs sharing information about the Google supplemental index and talking SEO strategies related to it. Just as a PSA, the Google supplemental index has not been in existence for a dozen or so years now.
Today, in 2022, there is no such thing as the Google Supplemental Index.
Yes, pre-2010, Google maintained two indexes for technical reasons. The main index was updated more frequently and faster and the supplemental index was for pages of lower importance that didn't need to be updated as quickly. Generally, pages in the main index would rank higher in Google Search than pages in the supplemental index. And Google would generally only rank pages in the supplemental index if it couldn't find good matches in the main index.
In fact, Google use to label search results that came from the supplemental index, as such. Here is a screenshot I posted back in 2007 with this label:
In December 2007, Google started to hide the supplemental index label, stating "We improved the crawl frequency and decoupled it from which index a document was stored in, and once these "supplementalization effects" were gone, the "supplemental result" tag itself—which only served to suggest that otherwise good documents were somehow suspect— was eliminated a few months ago. Now we're coming to the next major milestone in the elimination of the artificial difference between indices: rather than searching some part of our index in more depth for obscure queries, we're now searching the whole index for every query."
Then in 2009 Google started testing a new indexing method called Caffeine and in 2010, Google launched Caffeine fully. With that launch, Google stopped using the supplemental index all together. Heck, Google still uses Caffeine today...
In any event, John Mueller of Google was asked to confirm that the supplemental index is not longer and he said on Twitter it's safe to say that index from 2003 is now enjoying the great bit-bucket in the sky."
In 2007 we mentioned the difference was minimal ( https://t.co/7lVBkBlzVl , https://t.co/bxRIm1wyW2 ), in 2010 we revamped the indexing systems completely ( https://t.co/W9jVSD4D91 ) so it's safe to say that index from 2003 is now enjoying the great bit-bucket in the sky.
— 🐝 johnmu.csv (personal) 🐝 (@JohnMu) June 26, 2022
So don't let anyone confuse you or set you off in the wrong direction - Google's index works differently than it did pre-2010 than it does post-2010 and there is no supplemental index anymore.
Forum discussion at Twitter.
