On Fri, Apr 20, 2018 at 11:40 AM, Kyotaro HORIGUCHI <horiguchi.kyot...@lab.ntt.co.jp> wrote: > By the way, I think I found a bug of FPW. > > The following steps yields INSERT record that doesn't have a FPI > after a checkpoint. > > (Start server with full_page_writes = off) > CREATE TABLE t (a int); > CHECKPOINT; > INSERT INTO t VALUES (1); > ALTER SYSTEM SET full_page_writes TO on; > SELECT pg_reload_conf(); > CHECKPOINT; > INSERT INTO t VALUES (1); > > The last insert is expected to write a record with FPI but it > doesn't actually. No FPI will be written for the page after that. > > It seems that the reason is that XLogInsertRecord is forgetting > to check doPageWrites' update. > > In the failure case, fpw_lsn has been set by XLogRecordAssemble > but doPageWrite is false at the time and it considers that no FPI > is required then it sets fpw_lsn to InvalidXLogRecPtr. > > After that, XLogInsertRecord receives the record but it thinks > that doPageWrites is true since it looks the shared value. > >> if (fpw_lsn != InvalidXLogRecPtr && fpw_lsn <= RedoRecPtr && doPageWrites) > > So this line thinks that "no FPI is omitted in this record" but > actually the record is just forgotten to attach them. > > The attached patch lets XLogInsertRecord check if doPageWrites > has been turned on after the last call and cause recomputation in > the case. >
I think you have correctly spotted the problem and your fix looks good to me. As this is a separate problem and fix is different from what we are discussing here, I think this can be committed it separately. -- With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com
