I wrote a few patches, that we use in our production. These patches are small, but I hope, so its can be interesting for upstream:
1. cancel time - we log a execution time cancelled statements
2. fatal verbose - this patch ensure a verbose log for fatal errors. It simplify a investigation about reasons of error.
3. relation limit - possibility to set session limit for maximum size of relations. Any relation cannot be extended over this limit in session, when this value is higher than zero. Motivation - we use lot of queries like CREATE TABLE AS SELECT .. , and some very big results decreased a disk free space too much. It was high risk in our multi user environment. Motivation is similar like temp_files_limit.
4. track statement lock - we are able to track a locking time for query and print this data in slow query log and auto_explain log. It help to us with lather slow query log analysis.
Do you thinking so these patches can be generally useful?