I came to think that both of you are misunderstanding how synchronous standbys are choosed so I'd like to clarify the behavior.
At Fri, 22 Apr 2016 11:09:28 +0900 (Tokyo Standard Time), Kyotaro HORIGUCHI <horiguchi.kyot...@lab.ntt.co.jp> wrote in <20160422.110928.18809311.horiguchi.kyot...@lab.ntt.co.jp> > > > But this particular sentence seems to be talking > > > about what's the case for any given slot. > > > > Right, that's my reading also. In SyncRepInitConfig, every walsender sets sync_standby_priority by itself. The priority value is the index of its application_name in s_s_names list (1 based). When a walsender receives a feedback from walreceiver, it may release backends waiting for certain LSN to be secured. First, SyncRepGetSyncStandbys collects active standbys. Then it loops from the hightest priority value to pick up all of the active standbys for each priority value until all of the seats are occupied. Then SyncRepOldestSyncRepPtr calculates the oldest LSNs only among the standbys SyncRepGetSyncStandbys returned. Finally, it releases backends using the LSNs. In short, every 'slot' in s_s_names can corresponds to two or more *synchronous* standbys. The resulting behavior is as the following. > I don't certainly understnd what the 'sync slot' means. If it > means a name in a replication set description, that is, 'nameN' > in the following setting of s_s_names. > > '2(name1, name2, name3)' > > There may be two or more duplicates even in the > single-sync-age. But only one synchronous standby was allowed so > any 'sync slot' may have at least one matching synchronous > standby in the single-sync-age. This is what I see in the > sentense. Is this wrong? > > Now, we can have multiple synchronous standbys so, for example, > if three standbys with the name 'name1', two of them are choosed > as synchronous. This is a new behavior in the multi-sync-age and > syncrep.c has been changed so as to do so. > > For a supplemnet, the following case. > > '5(name1, name2, name3)' > > and the following standbys > > (name1, name1, name2, name2, name3, name3) This was a bad example, (name1, name1, name2, name2, name2, name2, name3) For this case, the followings are choosed as synchornous standby. (name1, name1, name2, name2, name2) Three of the four name2s are choosed but which name2s is an implement matter. > # However, 5 for three names causes a warning.. reegards, -- Kyotaro Horiguchi NTT Open Source Software Center -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
