At Fri, 27 Nov 2020 07:01:16 +0000, "tsunakawa.ta...@fujitsu.com" <tsunakawa.ta...@fujitsu.com> wrote in > From: Masahiko Sawada <sawada.m...@gmail.com> > > While testing the patch on some workload, I realized that > > XLOG_FPI_FOR_HINT record could still be emitted even when wal_level = > > none. IIUC that WAL record is not necessary during wal_level = none > > since the server cannot be the primary server and the server crash > > ends up requiring to restore the whole database. > > Nice catch! XLOG_FPI_FOR_HINT and XLOG_FPI should be eliminated, otherwise > large amount of WAL may be written. (It seems that other RMIDs than > RM_XLOG_ID and RM_XACT_ID do not have to be written.) > > 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"?
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? And, currenly what decides whether to emit a wal record according to wal_level is the caller of XLogInsert. 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. regards. -- Kyotaro Horiguchi NTT Open Source Software Center
