Hi Munro,
Thanks for cautioning us about possible memory leaks(during error cases)
incase of long-lived DSA segements(have a look in below thread for more
details).
https://www.postgresql.org/message-id/CAEepm%3D3c4WAtSQG4tAF7Y_VCnO5cKh7KuFYZhpKbwGQOF%3DdZ4A%40mail.gmail.com
Actually we are following an approach to avoid this DSA memory leaks. Let
me explain our implementation and please validate and correct us in-case we
miss anything.
Implementation:
Basically we have to put our index data into memory (Index Column Value
Vs Ctid) which we get in aminsert callback function.
Coming to the implementation, in aminsert Callback function,
We Switch to CurTransactionContext
Cache the DMLs of a transaction into dlist(global per process)
Even if different clients work parallel, it won't be a problem because every
client gets one dlist in separate process and it'll have it's own
CurTransactionContext
We have registered transaction callback (using RegisterXactCallback()
function). And during event pre-commit(XACT_EVENT_PRE_COMMIT), we populate all
the transaction specific DMLs (from dlist) into our in-memory index(DSA)
obviously inside PG_TRY/PG_CATCH block.
In case we got some errors(because of dsa_allocate() or something else) while
processing dlist(while populating in-memory index), we cleanup the DSA memory
in PG_CATCH block that is allocated/used till that point.
During other error cases, typically transactions gets aborted and PRE_COMMIT
event is not called and hence we don't touch DSA at that time. Hence no need to
bother about leaks.
Even sub transaction case is handled with sub transaction callbacks.
CurTransactionContext(dlist basically) is automatically cleared after that
particular transaction.
I want to know if this approach is good and works well in all cases. Kindly
provide your feedback on this.
Regards
G. Sai Ram
