due to bug 507790, during a UNION ALL underlying data in the queried tables can change, that means we can get any sort of random results (duplicates or missing results) from those queries. Even if UNION is slightly slower, we have to replace UNION ALLs with UNIONs, to get consistent results.

Note that any query that is only run asynchronously will not run into this issue, and so it doesn't need to be changed.

sure, i won't change all of them

using UNION instead of UNION ALL in queries that have a COALESCE between select fields causes WARNINGs for sorting operations, i suppose due to the fact UNION tries to discard duplicates, and that process will be quite slower then what we do actually. That happens in lots of queries. This patch is what we should do to replace UNION ALLs, Shawn what do you think? Imho this will kill perf in a bad way, one of the queries is mDBGetChildren, that is used (among other things) to populate all bookmarks folders (included the toolbar).

Bug 511965 should reduce cases where this happens.

if bug 511965 is ensuring functionality i'm goingto wontfix this. the perf drop would just be too big.

unfortunatly WONTFIX, performances regression would be quite bad.