Upgrade Query Load MySQL · RDS Oss · aws/agent-toolkit-for-aws · Skills Docs

Upgrade Query Load MySQL · RDS Oss · aws/agent-toolkit-for-aws · Skills Docs

SELECT DIGEST_TEXT, COUNT_STAR, SUM_TIMER_WAIT/1000000000000 AS total_time_sec,
  AVG_TIMER_WAIT/1000000000 AS avg_time_ms, SUM_ROWS_EXAMINED, SUM_ROWS_SENT,
  FIRST_SEEN, LAST_SEEN
FROM performance_schema.events_statements_summary_by_digest
WHERE SCHEMA_NAME NOT IN ('mysql','information_schema','performance_schema','sys')
ORDER BY SUM_TIMER_WAIT DESC LIMIT 5;

Pattern	Why It Matters in 8.0	Action
`using_temporary_table: true`	TempTable engine replaces MEMORY. Overflow goes to mmap, not MyISAM.	Tune `temptable_max_ram`. Monitor `Created_tmp_disk_tables`.
`using_filesort: true` + large rows	Sort algorithm changed.	Benchmark on test instance.
GROUP BY implicit sort relied upon	8.0 no longer implicitly sorts GROUP BY.	Add explicit ORDER BY.

Pattern	Why It Matters	Action
`Block Nested Loop` joins	8.0 may replace with hash join. Usually faster.	Test. Use `optimizer_switch` to disable hash_join if regression.
Derived table materialization	8.0 improved derived table merging.	Usually beneficial. Monitor.
`index_merge` usage	Behavior refined in 8.0.	Verify same indexes used post-upgrade.