Hi Henson, >> So, if RPR is active, WinSetMarkPosition() is not called at all? That >> seems too strong limitation. Can't we set mark at frameheadpos even >> if RPR is active? It seems safe since the only allowed franme start >> option is ROWS BETWEEN CURRENT ROW and we never step back to the rows >> before frameheadpos. > > > You raise a valid point. Setting mark at frameheadpos would be safe > for the window function's own read pointer, since we only allow > ROWS BETWEEN CURRENT ROW. > > However, the difficulty is with the PREV/NEXT navigation. In the > experimental patch, PREV accepts an optional offset argument -- > e.g. PREV(price, N) -- and this offset can be a runtime expression > whose value is not known until evaluation time. If the mark is > advanced to frameheadpos, PREV(price, N) with a large N could try > to access rows that the tuplestore has already truncated. > > This is why the experimental patch takes a different approach: it > creates a separate nav_winobj with its own mark pointer pinned at > position 0, so that the tuplestore never truncates rows that PREV > might need. The window function's own mark management is left > unchanged. > > The mark=0 approach is safe but conservative -- it prevents the > tuplestore from releasing any rows within the partition. The SQL > standard (ISO/IEC 19075-5, Subclause 5.6.2) requires the offset > argument to be a "runtime constant" -- meaning it cannot reference > columns or row pattern variables. So in practice, the maximum > offset is always known at plan time, which opens the door for a > future optimization: advance the mark to (currentpos - max_offset) > when all PREV offsets in the DEFINE clause are constant. > > Since the experimental patch redesigns how mark works for PREV/NEXT > navigation, I think we should drop 0004 from the current series > and revisit the set_mark question together with the experimental > patch. What do you think?
Agreed. So I just want to make sure I create v46 using 0001-0003 and 0005-0015. Am I correct? Best regards, -- Tatsuo Ishii SRA OSS K.K. English: http://www.sraoss.co.jp/index_en/ Japanese:http://www.sraoss.co.jp
