Most SEOs know that Google's database structure for storing content in their index is in shards. A database shard is a horizontal partition of data in a database or search engine. Each individual partition is referred to as a shard or database shard. Each shard is held on a separate database server instance, to spread load. Some data within a database remains present in all shards, but some only appears in a single shard. Each shard (or server) acts as the single source for this subset of data, says Wikipedia.
All that being said, Google says it doesn't matter where your page is in what shard, or how often it moves around.
Paul Haahr, one of the leads of Google search, said on Twitter "It doesn’t matter much." The question was posted by Ashley who wrote, "question on shards of you have a min- once a page gets sorted into a specific shard, does it stay there or does G shake 'em semi-regularly?"
Paul responded, "it doesn’t matter much is the high order bit. But they tend to move around very slowly."
Here are the set of tweets:
.@BermanHale It doesn’t matter much is the high order bit. But they tend to move around very slowly.
— Paul Haahr (@haahr) April 18, 2016
I am not sure how this can help anyone with their SEO, but hey, it is a question I never covered before (which is rare).
Forum discussion at Twitter.