At Fri, 27 Nov 2020 13:34:49 +0000, "osumi.takami...@fujitsu.com" <osumi.takami...@fujitsu.com> wrote in > Thank you, Horiguchi-San > > > I haven't seen a criteria of whether a record is emitted or not for > > wal_leve=none. > > > > We're emitting only redo logs. So I think theoretically we don't need > > anything > > other than the shutdown checkpoint record because we don't perform > > recovery and checkpoint record is required at startup. > > > > RM_XLOG_ID: > > XLOG_FPI_FOR_HINT - not needed? > > XLOG_FPI - not needed? > > > > XLOG_CHECKPOINT_SHUTDOWN - must have > > > > So how about the followings? > > XLOG_CHECKPOINT_ONLINE > > XLOG_NOOP > > XLOG_NEXTOID > > XLOG_SWITCH > > XLOG_BACKUP_END > > XLOG_PARAMETER_CHANGE > > XLOG_RESTORE_POINT > > XLOG_FPW_CHANGE > > XLOG_END_OF_RECOVERY > > > > > > RM_XACT_ID: > > XLOG_XACT_COMMIT > > XLOG_XACT_PREPARE > > XLOG_XACT_ABORT > > XLOG_XACT_COMMIT_PREPARED > > XLOG_XACT_ABORT_PREPARED > > XLOG_XACT_ASSIGNMENT > > XLOG_XACT_INVALIDATIONS > > > > Do we need all of these? > No. Strictly speaking, you are right. > We still have types of WAL that are not necessarily needed. > For example, XLOG_END_OF_RECOVERY is not useful > because wal_level=none doesn't recover from any accidents. > Or, XLOG_CHECKPOINT_ONLINE is used when we execute CHECKPOINT > not for shutting down. Thus we could eliminate more.
Yeah, although it's enough only to restrict non-harmful records practically, if we find that only a few kinds of records are needed, maybe it's cleaner to allow only required record type(s). > > And, currenly what decides whether to emit a wal record according to > > wal_level is the caller of XLogInsert. > Yes. > > > So doing this at XLogInsert-level means > > that we bring the criteria of the necessity of wal-record into xlog layer > > only for > > wal_level=none. I'm not sure it is the right direction. > I'm sorry. I didn't understand what "doing this" and "xlog layer" meant. "doing this" meant filtering record types. > Did you mean that fixing the caller side of XLogInsert (e.g. CreateCheckPoint) > is not the right direction ? Or, fixing the function of XLogInsert is not the > right direction ? Maybe it's right that if we can filter-out records looking only rmid, since the xlog facility doesn't need to know about record types of a resource manager. But if we need to finer-grained control on the record types, I'm afraid that that's wrong. However, if we need only the XLOG_CHECKPOINT_SHUTDOWN record, it might be better to let XLogInsert filter records rather than inserting that filtering code to all the caller sites. > > At Fri, 27 Nov 2020 07:01:16 +0000, "tsunakawa.ta...@fujitsu.com" > > <tsunakawa.ta...@fujitsu.com> wrote in > > > I'm afraid "none" doesn't represent the behavior because RM_XLOG_ID and > > RM_XACT_ID WAL records, except for XLOG_FPI_*, are emitted. What's the > > good name? IIUC, "minimal" is named after the fact that the minimal > > amount of WAL necessary for crash recovery is generated. "norecovery" or > > "unrecoverable"? > Lastly, I found another name which expresses the essential characteristic of > this wal_level. > How about the name of wal_level="crash_unsafe" ? > What did you think ? I don't dislike "none" since it seems to me practically "none". It seems rather correct if we actually need only the shutdown checkpoint record. "unrecoverable" is apparently misleading. "crash_unsafe" is precise but seems somewhat alien being among "logical", "replica" and "minimal". regards. -- Kyotaro Horiguchi NTT Open Source Software Center
