> PostmasterContext is set quite early in the procedure so it should not be a > problem to use it. I think we can use PostmasterContext rather than > TopMemoryContext. The memory for the allocations are passed down to > PostmasterMain() and used inside InitPostgres() but as far as I can tell, > they are not used after the InitPostgres() call. The PostmasterContex is > destroyed right after the call to InitPostgres() inside PostmasterMain() > and then the rest is allocated in other contexts.
Well, this is what PostgresMain has to say about it:
/* * If the PostmasterContext is still around, recycle the space; we don't * need it anymore after InitPostgres completes. Note this does not trash * *MyProcPort, because ConnCreate() allocated that space with malloc() * ... else we'd need to copy the Port data first. Also, subsidiary data * such as the username isn't lost either; see ProcessStartupPacket(). */ if (PostmasterContext) { MemoryContextDelete(PostmasterContext);
Ugh. Ok. Missed that comment.
So I think blowing away part of struct Port independently of the containing struct is a bad idea. Why isn't more appropriate to do what ConnCreate does?
if (!(port = (Port *) calloc(1, sizeof(Port)))) { ereport(LOG, (errcode(ERRCODE_OUT_OF_MEMORY), errmsg("out of memory"))); ExitPostmaster(1); }
... ugh. I have to admit that killing postmaster due to a transient out-of-memory makes me a bit nervous -- do note that this ExitPostmaster() happens before we've forked the backend, so this code does bring the server down (!!). If we want to make postmaster more robust in the face of OOM, we should also change this code somehow, yes?
Seems reasonable, yes. I'll see what I can throw together.
I agree with Mats' premise when starting the thread -- even if the server is not in great shape, it doesn't seem like taking the whole service down is a great response. It would be better to just refuse the connection with some error and let existing connections chug along, poorly though they can. Maybe they'll also die soon, freeing memory; but that'll be no good if Postmaster is gone altogether.
Now, it would be better if we could test this more thoroughly. Perhaps it's possible to use something like the mallocfail.c lib that Heikki wrote a few years ago, teaching it to handle calloc https://postgr.es/m/547480DE.4040408@vmware.com
Thanks. Will take a look at that.
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From:
Peter Eisentraut Date: Subject:
Re: BUG #17720: pg_dump creates a dump with primary key that cannot be restored, when specifying 'using index ...'