Thomas Orozco 134bd04fb9 mononoke: introduce BookmarksSubscription ... Summary: This introduces a mechanism to query bookmark updates from the bookmarks update log instead of via the bookmarks table. The end goal is to use this in the warm bookmarks cache (WBC). Note that the WBC cannot currently work if we just give it updates. For example, if we give it an updated bookmark, then the update fails, the WBC won't attempt to update it again. So, we need to maintain a view of all bookmarks, and expose that to the WBC (instead of exposing a stream of changes). Historically, the WBC has just materialized this from SQL every second when it needs it, so there's not much difference in terms of peak resource usage here anyway. Note that we are missing some information in our update log to be able to maintain bookmarks just from that (we don't really track what kind of update it was, we need to infer that, and we're missing changes of kind). Conversely, we're missing some information in the bookmarks table itself (if a bookmark gets deleted there is no row we can use to see that). The way this works is that we query the bookmarks update log and join with the bookmarks table to find matching rows (which we can do via the `log_id` we insert there). This gives us the bookmark kind and cs id. It also gives us which bookmarks were deleted: we just won't find a match. Note that individual queries in MySQL (or transactions with repeatable read) don't experience tearing, so as long as the bookmark and its log entry were inserted in the same transaction, we should find both here. Reviewed By: StanislavGlebik Differential Revision: D28478398 fbshipit-source-id: 1a307a90148bb60b50fa6008dff8f24ec8e1d5ea		2021-05-20 07:08:39 -07:00
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main.rs	mononoke: introduce BookmarksSubscription	2021-05-20 07:08:39 -07:00