If you have queried v$sgastat on recent Oracle versions (by which I mean 9i and above) you probably have seen allocations for some sort of simulators in Oracle instance. Here’s an example:
SQL> select * from v$sgastat where lower(name) like '%sim%' order by name; POOL NAME BYTES ------------ -------------------------- ---------- shared pool kglsim alloc latch area 1700 shared pool kglsim alloc latches 68 shared pool kglsim count of pinned he 9248 shared pool kglsim free heap list 204 shared pool kglsim free obj list 204 shared pool kglsim hash table 4104 shared pool kglsim hash table bkts 2097152 shared pool kglsim heap 635536 shared pool kglsim latch area 1700 shared pool kglsim latches 68 shared pool kglsim main lru count 87040 shared pool kglsim main lru size 174080 shared pool kglsim object batch 909440 shared pool kglsim pin list arr 816 shared pool kglsim recovery area 2112 shared pool kglsim sga 22092 shared pool kglsim size of pinned mem 18496 shared pool ksim client list 84 shared pool log_simultaneous_copies 480 shared pool sim cache nbufs 640 shared pool sim cache sizes 640 shared pool sim kghx free lists 4 shared pool sim lru segments 640 shared pool sim segment hits 1280 shared pool sim segment num bufs 640 shared pool sim state object 48 shared pool sim trace buf 5140 shared pool sim trace buf context 120 shared pool sim_knlasg 1200 shared pool simulator hash buckets 16512 shared pool simulator latch/bucket st 4608 31 rows selected.
See, a bunch of “kgl sim” and then just “sim” allocations.
… or sometimes you can see latch contention on following latches:
SQL> select name from v$latch where name like '%sim%'; NAME ------------------------------------------------------- ksim membership request latch simulator lru latch simulator hash latch sim partition latch shared pool simulator shared pool sim alloc 6 rows selected.
Again, there seems to be some “simulation” work going on in Oracle instance.
So what are these simulators about?
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