Fix performance issue with many duplicate ids #40
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If you had a sync rules query like this:
select '' as id from mytable(all rows with the same id), the JOIN sync_local query would haveO(n^2)operations. For 10k rows, this is 100m operations, which takes a very long time.While this should never be the case in a production app (you'd typically have a max of 2 or 3 duplicates), it could easily lead to a "hanging" app during development if you had a mistake in the query, making it difficult to debug.
The change in query here takes it back to
O(n). It does use an additional "TEMP B-TREE" for the DISTINCT/UNION step, but does not seem to negatively affect sync performance in my testing.