On 2016-06-08 10:04:56 +0530, Amit Kapila wrote: > On Tue, Jun 7, 2016 at 11:01 PM, Andres Freund <and...@anarazel.de> wrote:> > > I think if we go with the pg_check_visibility approach, we should also > > copy the other consistency checks from vacuumlazy.c, given they can't > > easily be triggered. > > Are you referring to checks that are done in lazy_scan_heap() for each > block?
Yes. > I think the meaning full checks in this context could be (a) page > is marked as visible, but corresponding vm is not marked. (b) page is > marked as all visible and has dead tuples. (c) vm bit indicates frozen, but > page contains non-frozen tuples. Yes. > I think right now the design of pg_visibility is such that it returns the > required information at page level to user by means of various functions > like pg_visibility, pg_visibility_map, etc. If we want to add page level > checks in this new routine as well, then we have to think what should be > the output if such checks fails, shall we issue warning, shall we return > information in some other way. Right. > Also, I think there will be some duplicity > with the already provided information via other functions of this module. Don't think that's a problem. One part of the functionality then is returning the available information, the other is checking for problems and only returning problematic blocks. > > Wonder how we can report both block and tuple > > level issues. Kinda inclined to report everything as a block level > > issue? > > > > The way currently this module provides information, it seems better to have > separate API's for block and tuple level inconsistency. For block level, I > think most of the information can be retrieved by existing API's and for > tuple level, this new API can be used. I personally think simplicity is more important than detail here; but it's not that important. If this reports a problem, you can look into the nitty gritty using existing functions. Andres -- Sent via pgsql-hackers mailing list (email@example.com) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers