Rough checklist (at least as start point) for database stuff:
0.Wrong SQL query (perhaps with cartesian product) filling up db/tempdb space.
1. Inadequate statistics on tables (not updated, updated on "empty" tables,sps not recompiled) (=>needs to "update" bad plan to the good one somehow)
2. Dropped index (table scan instead of index is running) (=>setup index)
3. Fragmentation (=> drop/rectrate cl.index or reorg rebuild)
4. Db cache does not have enough memory and server has to read from disk.(=>incr. memory, bind db)
5.CPU (Unix server busy by something else) (=> drop something else)
6. Locking contention (one process is waiting for other to release lock on some table/page/row) (=> change appl.logic )
7. Network slowness (=>tcp_no_delay)
8. Table corrupt (=>dbcc)
9. User connections not enough (=>sp_configure)
10. Stacktraces in Syb.errorlog with infected by 11, server might be not stable afterward (=>restart).
11. Log suspended.(everything is wating till trlog dump or increase happened) at that time. (=>dump trlog)
12. Too often commit (=> batch)
13. Log and data not separated (=> separate)
14. Run sp_sysmon