Commits on Apr 2, 2024

1. Removed use of subqueries in email analytics queries …

   closes https://linear.app/tryghost/issue/ENG-790/remove-use-of-sub-queries-in-email-analytics
   
   Avoiding sub queries means we don't have a process tied up for longer than necessary and we can more easily see if one of the queries is non-performant.
   
   - extracted the count queries into separate queries and used the retrieved values in the final update query
   - removed a query by moving the email open rate calculation into JS as we've already fetched the necessary data before that point

   

   kevinansfield committed Apr 2, 2024
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2. Optimised email stats aggregation query for typical column usage …

   ref https://linear.app/tryghost/issue/ENG-790/remove-use-of-sub-queries-in-email-analytics
   
   - the `delivered_at` column is typically entirely/nearly entirely filled with values meaning the `IS NOT NULL` query matches a huge number of rows that MySQL has to fetch from the index to count
   - using `IS NULL` switches that behaviour around as it will now match very few rows which has been shown in testing to be considerably quicker
   - after switching to `IS NULL` the query returns an "undelivered" count rather than a "delivered" count, in order to keep the rest of the system behaviour the same we can calculate the delivered count by subtracting the query result from the total number of emails sent which we can fetch using a very fast primary key lookup query on the `emails` table

   

   kevinansfield committed Apr 2, 2024
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