At Tue, 6 Apr 2021 04:11:35 +0000, "osumi.takami...@fujitsu.com" <osumi.takami...@fujitsu.com> wrote in > On Tuesday, April 6, 2021 9:41 AM Fujii Masao <masao.fu...@oss.nttdata.com> > > On 2021/04/05 23:54, osumi.takami...@fujitsu.com wrote: > > >> This makes me think that we should document this risk.... Thought? > > > +1. We should notify the risk when user changes > > > the wal_level higher than minimal to minimal to invoke a carefulness > > > of user for such kind of operation. > > > > I removed the HINT message "or recover to the point in ..." and added the > > following note into the docs. > > > > Note that changing <varname>wal_level</varname> to > > <literal>minimal</literal> makes any base backups taken before > > unavailable for archive recovery and standby server, which may > > lead to database loss. > Thank you for updating the patch. Let's make the sentence more strict. > > My suggestion for this explanation is > "In order to prevent database corruption, changing > wal_level to minimal from higher level in the middle of > WAL archiving requires careful attention. It makes any base backups > taken before the operation unavailable for archive recovery > and standby server. Also, it may lead to whole database loss when > archive recovery fails with an error for that change. > Take a new base backup immediately after making wal_level back to higher > level."
The first sentense looks like somewhat nanny-ish. The database is not corrupt at the time of this error. We just lose updates after the last read segment at this point. As Fujii-san said, we can continue recoverying using crash recovery and we will reach having a corrupt database after that. About the last sentense, I prefer more flat wording, such as "You need to take a new base backup..." > Then, we can be consistent with our new hint message, > "Use a backup taken after setting wal_level to higher than minimal.". > > Is it better to add something similar to "Take an offline backup when you > stop the server > and change the wal_level" around the end of this part as another option for > safeguard, also? Backup policy is completely a matter of DBAs. If flipping wal_level alone highly causes unstartable corruption,,, I think it is a bug. > For the performance technique part, what we need to explain is same. Might be good, but in simpler wording. > Another minor thing I felt we need to do might be to add double quotes to > wrap minimal in errhint. Since the error about hot_standby has gone, either will do for me. > Other errhints do so when we use it in a sentence. > > There is no more additional comment from me ! regards. -- Kyotaro Horiguchi NTT Open Source Software Center
