Thanks for replay.I feel confused about snapshot. At 2019-10-23 11:51:19, "Kyotaro Horiguchi" <horikyota....@gmail.com> wrote: >Hello. > >At Tue, 22 Oct 2019 20:42:21 +0800 (CST), Thunder <thund...@126.com> wrote in >> Update the patch. >> >> 1. The STANDBY_SNAPSHOT_PENDING state is set when we replay the first >> XLOG_RUNNING_XACTS and the sub transaction ids are overflow. >> 2. When we log XLOG_RUNNING_XACTS in master node, can we assume that all >> xact IDS < oldestRunningXid are considered finished? > >Unfortunately we can't. Standby needs to know that the *standby's* >oldest active xid exceeds the pendig xmin, not master's. And it is >already processed in ProcArrayApplyRecoveryInfo. We cannot assume that
>the oldest xids are not same on the both side in a replication pair. This issue occurs when master does not commit the transaction which has lots of sub transactions, while we restart or create a new standby node. The standby node can not provide service because of this issue. Can the standby have any active xid while it can not provide service? > >> 3. If we can assume this, when we replay XLOG_RUNNING_XACTS and change >> standbyState to STANDBY_SNAPSHOT_PENDING, can we record oldestRunningXid to >> a shared variable, like procArray->oldest_running_xid? >> 4. In standby node when call GetSnapshotData if >> procArray->oldest_running_xid is valid, can we set xmin to be >> procArray->oldest_running_xid? >> >> Appreciate any suggestion to this issue. > >At 2019-10-22 01:27:58, "Robert Haas" <robertmh...@gmail.com> wrote: >>On Mon, Oct 21, 2019 at 4:13 AM Thunder <thund...@126.com> wrote: >.. >> >I think that the issue you've encountered is design behavior. In >> >other words, it's intended to work that way. >> > >> >The comments for the code you propose to change say that we can allow >> >connections once we've got a valid snapshot. So presumably the effect >> >of your change would be to allow connections even though we don't have >> >a valid snapshot. >> > >> >That seems bad. > >regards. > >-- >Kyotaro Horiguchi >NTT Open Source Software Center >
