On Fri, 2006-09-29 at 11:55 -0400, Tom Lane wrote: > Simon Riggs <simon@xxxxxxxxxxxxxxx> writes: > > PreallocXlogFiles() adds only a *single* xlog file, sometimes. > > Hm, you are right. I wonder why it's so unaggressive ... perhaps > because under normal circumstances we soon settle into a steady > state where each checkpoint recycles the right number of files. That is normally the case, yes. But only for people that have correctly judged (or massively overestimated) what checkpoint_segments should be set at. Currently, when we don't have enough we add one, maybe. When we have too many we truncate right back to checkpoint_segments as quickly as possible. Seems like we should try and automate that completely for 8.3: - calculate the number required by keeping a running average which ignores a single peak value, yet takes 5 consistently high values as the new average - add more segments with increasing aggressiveness 1,1,2,3,5,8 segments at a time when required - handle out-of-space errors fairly gracefully by waking up the archiver, complaining to the logs and then eventually preventing transactions from writing to logs rather than taking server down - shrink back more slowly by halving the difference between the overlimit and the typical value - get rid of checkpoint_segments GUC That should handle peaks caused by data loads, archiving interruptions or other peak loadings. -- Simon Riggs EnterpriseDB http://www.enterprisedb.com
