At Wed, 13 Jan 2021 06:01:34 +0000, "tsunakawa.ta...@fujitsu.com" <tsunakawa.ta...@fujitsu.com> wrote in > From: Kyotaro Horiguchi <horikyota....@gmail.com> > > XLogBeginInsert(); > > XLogSetRecrodFlags(XLOG_MARK_ESSENTIAL); # new flag value > > XLOGInsert(....); > > Oh, sounds like a nice idea. That's more flexible by allowing WAL-emitting > modules to specify which WAL records are mandatory even when wal_level is > none. > > For example, gistXLogAssignLSN() adds the above flag like this: > > XLogBeginInsert(); > XLogSetRecordFlags(XLOG_MARK_UNIMPORTANT | XLOG_MARK_ESSENTIAL); > XLogRegisterData((char *) &dummy, sizeof(dummy)); > > (Here's a word play - unimportant but essential, what's that?)
Hmm. Food may not be important to someone but it is essential for survival. I think this is somethig like that :p > And the filter in XLogInsert() becomes: > > + if (wal_level == WAL_LEVEL_NONE && > + !((rmid == RM_XLOG_ID && info == XLOG_CHECKPOINT_SHUTDOWN) || > + (rmid == RM_XLOG_ID && info == XLOG_PARAMETER_CHANGE) || > + (rmid == RM_XACT_ID && info == XLOG_XACT_PREPARE) || > + (curinsert_flags & XLOG_MARK_ESSENTIAL))) > > Or, > > + if (wal_level == WAL_LEVEL_NONE && > + !(curinsert_flags & XLOG_MARK_ESSENTIAL)) > > and add the new flag when emitting XLOG_CHECKPOINT_ONLINE, Yeah, I was going to comment about that. Skipping the record makes controlfile filled by a bogus checkpoint location. > XLOG_PARAMETER_CHANGE and XLOG_PREPARE records. I think both have > good reasons: the former centralizes the handling of XACT and XLOG > RM WAL records (as the current XLOG module does already), and the > latter delegates the decision to each module. Which would you > prefer? (I kind of like the former, but this is a weak opinion.) Unfortunately, I prefer the latter as it is simple because it is in a hot path. As I think I mentioned upthread, I think the xlog stuff should refrain from being conscious of things deeper than RMger-ID level. One of other reasons is that generally the issuer site is the authoritative about the importance and essentiality of a record being issued. And I don't think it's very good to do the same thing in different ways at the same time. Fortunately each type of the recrods has only few issuer places. By the way, I noticed that pg_switch_wal() silently skips its task. Desn't it need to give any sort of ERROR? regards. -- Kyotaro Horiguchi NTT Open Source Software Center
