Hello Andres,
> I can think of a number of relatively easy ways to address this:
> 1) Just zap (or issue?) all pending flush requests when getting an
> smgrinval/smgrclosenode
> 2) Do 1), but filter for the closed relnode
> 3) Actually handle the case of the last open segment not being
> RELSEG_SIZE properly in _mdfd_getseg() - mdnblocks() does so.
>
> I'm kind of inclined to do both 3) and 1).
Alas I'm a little bit outside my area of expertise. Just for suggestion
purpose, possibly totally wrong (please accept my apology if this is the
case), the ideas I had while thinking about these issues, some may be
quite close to your suggestions above:
- keep track of file/segment closing/reopenings (say with a counter), so that if a flush is about a file/segment
whichhas been closed or reopened, it is just skipped. I'm not sure this is enough, because one process may do the
filecleaning and another may want to flush, although I guess there is some kind of locking/shared data structures to
manage such interactions between pg processes.
- because of "empty the bucket when filled behavior" of the current implementation, a buffer to be flused may be
keptfor a very long time in the bucket. I think that flushing advices become stale after a while so should not be
issued(the buffer may have been written again, ...), or the bucket should be flushed after a while even of not
full.
Also, a detail in "pg_flush_data", there are a serie of three if/endif,
but it is not obvious to me whether they are mutually exclusive while
looking at the source, so I was wondering whether the code could try
several flushings approaches one after the other... This is probably not
the case, but I would be more at ease with a if/elif/elif/endif structure
there so that is clearer.
--
Fabien.
