Re: unsafe use of hash_search(... HASH_ENTER ...)

"Qingqing Zhou" <zhouqq@cs.toronto.edu> writes:
> Consider the senario like this:

> Backends register some dirty segments in BgWriterShmem->requests; bgwrite
> will AbsorbFsyncRequests() asynchornously but failed to record some one in
> pendingOpsTable due to an "out of memory" error. All dirty segments
> remembered in "requests" after this one will not have chance be absorbed by
> bgwriter.

So really we have to PANIC if we fail to record a dirty segment.  That's
a bit nasty, but since the hashtable is so small (only 16 bytes per
gigabyte-sized dirty segment) it seems unlikely that the situation will
ever occur in practice.

I'll put a critical section around it --- seems the easiest way to
ensure a panic ...
        regards, tom lane