On 7/24/21, 8:10 PM, "Fujii Masao" <masao.fu...@oss.nttdata.com> wrote: > On 2021/07/25 7:50, Andres Freund wrote: >> Hi, >> >> I've been repeatedly confused by the the number of WAL files supposedly >> added. Even when 100s of new WAL files are created the relevant portion >> of log_checkpoints will only ever list zero or one added WAL file. >> >> The reason for that is that CheckpointStats.ckpt_segs_added is only >> incremented in PreallocXlogFiles(). Which has the following comment: >> * XXX this is currently extremely conservative, since it forces only one >> * future log segment to exist, and even that only if we are 75% done with >> * the current one. This is only appropriate for very low-WAL-volume >> systems. >> >> Whereas in real workloads WAL files are almost exclusively created via >> XLogWrite()->XLogFileInit(). >> >> I think we should consider just removing that field. Or, even better, show >> something accurate instead. > > +1 to show something accurate instead. > > It's also worth showing them in monitoring stats view like pg_stat_wal?
+1. I was confused by this when working on a WAL pre-allocation patch [0]. Perhaps it could be replaced by a new parameter and a new field in pg_stat_wal. How about something like log_wal_init_interval, where the value is the minimum amount of time between reporting the number of WAL segments created since the last report? Nathan [0] https://www.postgresql.org/message-id/flat/20201225200953.jjkrytlrzojbn...@alap3.anarazel.de
