On Fri, Sep 10, 2021 at 12:20 PM Mark Dilger <mark.dil...@enterprisedb.com> wrote: > A better example may be found in ginmetapage.c: > > needwal = RelationNeedsWAL(indexrel); > if (needwal) > { > CheckWALPermitted(); > computeLeafRecompressWALData(leaf); > } > > /* Apply changes to page */ > START_CRIT_SECTION();
Yeah, that looks sketchy. Why not move CheckWALPermitted() down a line? > Even if CheckWALPermitted is assumed to be close enough to atomic to not be a > problem (I don't agree), that argument can't be made here, as > computeLeafRecompressWALData is not trivial and signals could easily be > processed while it is running. I think the relevant question here is not "could a signal handler fire?" but "can we hit a CHECK_FOR_INTERRUPTS()?". If the relevant question is the former, then there's no hope of ever making it work because there's always a race condition. But the signal handler is only setting flags whose only effect is to make a subsequent CHECK_FOR_INTERRUPTS() do something, so it doesn't really matter when the signal handler can run, but when CHECK_FOR_INTERRUPTS() can call ProcessInterrupts(). -- Robert Haas EDB: http://www.enterprisedb.com